The History of Sauces in Europe

Ancient Times

The Middle Ages: Refinement and Concentration

Early Modern Sauces: Meat Essences, Emulsions

The Classic French System: Carême and Escoffier

Sauces in Italy and England

Modern Sauces: Nouvelle and Post-Nouvelle

The Science of Sauces: Flavor and Consistency

Flavor in Sauces: Taste and Smell

Sauce Consistency

The Influence of Consistency on Flavor

Sauces Thickened with Gelatin and Other Proteins

The Uniqueness of Gelatin

Extracting Gelatin and Flavor from Meats

Meat Stocks and Sauces

Commercial Meat Extracts and Sauce Bases

Fish and Shellfish Stocks and Sauces

Other Protein Thickeners

Solid Sauces: Gelatin Jellies and Carbohydrate Jellies

Jelly Consistency

Jellies from Meat and Fish: Aspics

Other Jellies and Gelées; Manufactured Gelatins

Carbohydrate Gelling Agents: Agar, Carrageenan, Alginates

Sauces Thickened with Flour and Starch

The Nature of Starch

Different Starches and Their Qualities

The Influence of Other Ingredients on Starch Sauces

Incorporating Starch into Sauces

Starch in Classic French Sauces

Gravy

Sauces Thickened with Plant Particles: Purees

Plant Particles: Coarse and Inefficient Thickeners

Fruit and Vegetable Purees

Nuts and Spices as Thickeners

Complex Mixtures: Indian Curries, Mexican Moles

Sauces Thickened with Droplets of Oil or Water: Emulsions

The Nature of Emulsions

Guidelines for Successful Emulsified Sauces

Cream and Butter Sauces

Eggs as Emulsifiers

Cold Egg Sauces: Mayonnaise

Hot Egg Sauces: Hollandaise and Béarnaise

Vinaigrettes

Sauces Thickened with Bubbles: Foams

Making and Stabilizing Foams

Salt

Salt Production

Kinds of Salt

Salt and the Body

Sauces are liquids that accompany the primary ingredient in a dish. Their purpose is to enhance the flavor of that ingredient — a portion of meat or fish or grain or vegetable — either by deepening and broadening its own intrinsic flavor, or by providing a contrast or complement to it. While the meat or grain or vegetable is always more or less itself, a sauce can be anything the cook wants it to be, and makes the dish a richer, more various, more satisfying composition. Sauces help the cook feed our perpetual hunger for stimulating sensations, for the pleasures of taste and smell, touch and sight. Sauces are distillations of desire.

The word sauce comes from an ancient root word meaning “salt,” which is the original concentrated flavoring, pure mineral crystals from the sea (p. 639). Our primary foods — animal flesh, grains and breads and pastas, starchy vegetables — are pretty bland, and cooks have found or invented a vast range of ingredients with which to make them more flavorful. The simplest are seasonings provided by nature: salt, pungent black pepper and chillis, sour juices of unripe fruits, sweet honey and sugar, distinctively aromatic herbs and spices. More complex are prepared condiments, many of them foods preserved and transformed by fermentation: sour and aromatic vinegar, salty and savory soy sauce and fish sauce, salty and sour pickles, pungent and sour mustard, sweet and sour and fruity ketchup. And then there are s auces, the ultimate composed flavorings. The cook conceives and prepares sauces for particular dishes, and can give them any flavor. They always include seasonings, sometimes condiments, and sometimes artfully intensified flavors of the primary foods themselves, or of other foods, or of the cooking process.

In addition to their heightened flavor, sauces give tactile pleasure by the way they move in the mouth. Cooks construct sauces to have a consistency somewhere between the resistant solidity of animal or plant tissues and the elusive thinness of water. This is the consistency of luscious ripe fruit that melts in the mouth and seems to feed us willingly, and of the fats that give a persistent, moist fullness to animal flesh and to cream and butter. The fluidity of a sauce allows it to coat the solid food evenly and lend it a pleasing moistness, while the substantial, lingering quality helps the sauce cling to the food and to our tongue and palate as well, prolonging the experience of its flavor and providing a sensation of richness.

A last pleasure that a sauce can provide is an attractive appearance. Many sauces are nondescript, but others have the vibrant color of their parent fruit or vegetable, or the depth of tone that comes with roasting and long cooking. Some have an attractive sheen, and some are intriguingly transparent. The visual beauty of a sauce is a sign of the care with which it was made, a suggestion of intensity and clarity of flavor and of presence on the tongue: an anticipation of pleasures to come.

There are several basic ways of making sauces. Many of them involve disrupting organized plant and animal tissues and freeing the juices that carry their flavor. Once extracted from their source, the juices can be combined with other flavorful materials, and then often benefit from thickening to help them linger on the food and in the mouth. The cook thickens juices by filling them with a variety of large molecules or particles that obstruct the flow of the water molecules. Most of this chapter deals with different thickening methods and their applications.

Sauces are closely related to two other basic preparations. Soups are also liquid foods of various consistencies, and may differ from sauces only in being somewhat less concentrated in flavor, so that they can be eaten as a food in themselves, not an accent. And jellies are thickened liquids with enough gelatin in them to set at room temperature, thus becoming a temporarily solid food that melts into a sauce in the mouth.

The History of Sauces
In europe

Europe is just one of several regions in the world that have evolved sauces with broad appeal in modern times. Many sauces are now popular far from their birthplaces, among them Chinese soy-based sauces, Indian sauces thickened and flavored with spices, and Mexican salsas and chillithickened moles. But it was in Europe, more precisely in France, that generations of cooks developed sauce making into a systematic art, and made it the heart of a national cuisine that became an international standard.

Ancient Times

Our first real knowledge of sauce-like preparations in Europe comes from Roman times. A Latin poem from around 25 CE describes a peasant farmer making a spread of pounded herbs, cheese, oil, and vinegar — an ancestor of pesto genovese — that gave a pungent, salty, aromatic savor to his flatbread (see box, p. 583).

A few centuries later, the Latin recipe book attributed to Apicius makes it clear that sauces played an essential part in the dining of the Roman elite. More than a quarter of the nearly 500 recipes are for sauces, the term for which was ius, the ancestor of our “juice.” Most contained at least a half dozen herbs and spices, as well as vinegar and/or honey, and some form of the fermented fish sauce garum (p. 235), which provided saltiness, savoriness, and a distinctive aroma (much as anchovies do today). And they were thickened in a variety of ways: with the pounded flavorings themselves; with pounded nuts or rice; with pounded liver or sea urchins; with pounded bread, pieces of pastry, and with pure wheat starch itself; with egg yolks, both raw and cooked. The sauce maker’s most important tool was clearly the mortar, but the sea urchins, eggs, and starch are early versions of more refined thickening methods.

The Middle Ages: Refinement
and Concentration

We don’t know much about cooking in Europe between the time of Apicius and the 14th century, the period from which a number of manuscript recipe collections survive. In some respects, sauce making hadn’t changed much. Medieval sauces often contained many spices, the mortar and pestle still pounded ingredients — now including meats and vegetables — and most of the Roman thickeners were still used. Bread was most common, toasted to provide additional color and flavor, while pure starch was no longer used, and cream and butter still weren’t.

New Flavors, New Clarity, and Jellies But there were some important differences, and genuine progress. Fish sauce had disappeared, its place taken by vinegar and unripe grape juice, or verjus. Thanks in part to the Crusades, which brought Europeans to the Middle East and into contact with Arab trade and traditions, many local Mediterranean flavorings had been displaced by exotic imports from Asia, especially cinnamon, ginger, and grains of paradise; and the nut of choice for thickening was now the almond. The mortar was joined by a second indispensable utensil: the cloth sieve or strainer (French étamine or tamis) through which sauces were passed to remove coarse particles of spice and thickener and produce a finer consistency. Cooks had discovered the principle of thickening meat broths by concentration — by boiling off unwanted water — and so developed both the consommé and the solid jelly, part of whose value was the way it could coat cooked meat or fish and protect it from the air and spoilage. The transparency of clear jellies in turn led by the 15th century to an improved strainer for removing the tiniest particles from them: a protein “fabric” of whipped egg whites that clarified the liquid from within.

Sauce Terminology Another important development during the Middle Ages was the elaboration of a new vocabulary for sauces and other flavorful fluids, and a more systematic approach to them. The Roman term ius was replaced by derivatives of the Latin salsus, meaning “salted”: sauce in France, salsa in Italy and Spain. In French, jus came to mean meat juices; bouillon was a stock produced by simmering meat in water; coulis was a thickened meat preparation that gave flavor and body to sauces, to potages — substantial soups — and other prepared dishes. The French soupe was the equivalent of the English sop, a flavorful liquid imbuing a piece or pieces of bread. A number of manuscripts divide their recipes into categories: there are uncooked sauces, cooked sauces, sauces in which to cook meat, and others with which to serve meats, thin and thick potages, and so on. And the English word gravy appears, derived apparently but mysteriously from the French grané. The latter, whose name derives from the Latin granatus, “made with grains, grainy,” was a kind of stew made with meat and meat juices, and not a separate mixture of spices and liquid.

Early Modern Sauces:
Meat essences, Emulsions

It’s in the three centuries between 1400 and 1700 that the sauces of our own time have their roots. Recipes call for fewer spices and a lighter hand with them; vinegar and verjus begin to give way to lemon juice; coarse bread and almond thickeners are replaced by flour and by butter and egg emulsions (see box, p. 585). And in France, meat broths become the central element of fine cooking. This is the era in which experimental science began to flourish, and some influential French cooks conceived of themselves as the chemists — or alchemists — of meat. Around 1750, François Marin echoed the Chinese description of flavor harmony from 2,000 years before, but with some telling twists (see box below).

Both Marin and I Yin speak of harmony and balance. But the Chinese cauldron brings together sweet, sour, bitter, salty, and pungent ingredients, while the French pot contains only meat juices, and generates complexity and harmony by concentrating them. Marin said that “Good taste has forbidden the burning juices and caustic ragouts of the ancienne cuisine,” with their Asian spices and abundant vinegar and verjus. Meat bouillon was now “the soul of cooking.” The meat’s juices are its essence, and the cook extracts them, concentrates them, and then uses them to imbue other foods with their flavor and nourishment. The purpose of a sauce is not to add new flavors to a food, but to deepen its flavor and integrate it with the underlying flavor of the other dishes.

Many of these preparations required prodigious amounts of flesh, the solid part of which did not appear in the final dish. A small amount of consommé, for example, was made with 2 lb/1 kg each of beef and veal, two partridges, a hen, and some ham. This meat was first cooked with some bouillon — itself already a meat extract — until the liquid bouillon and meat juices evaporated, and the meat began to stick to the pan and caramelize. Then yet more bouillon was added along with some vegetables, the mixture cooked for four hours, and strained to produce a liquid “yellow like gold, mild, smooth, and cordial.”

The Flowering of French Sauces Marin called his collection of bouillons, potages, jus, consommés, restaurants (“restoring” soups), coulis, and sauces “the foundation of cooking,” and said that by adopting a systematic approach to them, even a bourgeois family with limited resources would be “able to imagine an infinity of sauces and different stews.” French cookbooks soon began to include dozens of different soups and sauces, and several of the classic sauces were soon developed and named. Among these were alternatives to the meat-juice preparations, including two egg-emulsified sauces, hollandaise and mayonnaise, and the economical béchamel, the basic, neutral white sauce of milk, butter, and flour. But the great majority of sauces were made from meat, and meat juices were the underlying, unifying element in French cooking.

The Classic French System:
Carême and Escoffier

In 1789 came the French Revolution. The great houses of France were much reduced, and their cooks no longer had unlimited help and resources. Some lost their positions, and survived by opening the first fine restaurants. The culinary impact of these upheavals was assessed by the renowned chef Antonin Carême (1784–1833). In the “Preliminary Discourse” to his Maître d’Hôtel français, he noted that the “splendor of the old cuisine” was made possible by the lavish expenditures of the master on personnel and materials. After the Revolution, cooks lucky enough to retain a position

Restaurants too brought improvements; “in order to flatter the public taste,” the commercial chefs had to come up with novel, ever more “elegant” and “exquisite” preparations. So social revolution became a new motivating force for culinary progress.

Sauce Families Carême made a number of contributions to this progress, and perhaps the most notable involved the sauces. His idea, set forth in The Art of French Cooking in the 19th Century, was to organize the infinity of possibilities that Marin foresaw, and thereby help cooks realize them. He classified the sauces of the time into fourfamilies, each headed by a basic or leading sauce, and each expandable by playing variations on that basic theme. Only one of the leading sauces, espagnole, was based on expensive, highly concentrated meat extract; both velouté and allemande used unreduced stock, and béchamel used milk. Many of these sauces were thickened with flour, which is much more economical than reduced meat bouillon. This approach suited the limits and needs of postrevolutionary cuisine. The parent sauces could be prepared in advance, with the novel but minor modifications and seasonings to be done at the last minute on the day of the meal. As Raymond Sokolov puts it in his guide to the classic sauces, The Saucier’s Apprentice, these sauces were conceived as “convenience foods at the highest level.”

Less than a century after Carême, the great compilation of classic French cuisine, Auguste Escoffier’s Guide Culinaire (1902), lists nearly 200 different sauces, not including dessert sauces. And Escoffier attributed the eminence of French cooking directly to its sauces. “The sauces represent the partie capitale of the cuisine. It is they which have created and maintained to this day the universal preponderance of French cuisine.”

Of course this flavoring system was the creation of the line of professional cooks going back to medieval times. Alongside it there developed a more modest domestic tradition, which is accomplished in its own way. Disinclined to the labor and expense of long-simmered stocks and sauces, middle-class home cooks refined other methods: for example, making a broth from the trimmings of a roast, using the broth to dissolve the flavorful crust from the roasting pan, and boiling this relatively small amount of liquid to reduce and thicken it, or binding it with cream or flour.

Sauces in Italy and England

Purees and Meat Juices From the Middle Ages through the 16th century, Italian court cooking was as innovative as French cooking, and sometimes more so. Yet it stagnated in the 17th century, according to historian Claudio Benporat, as part of a general political and cultural decline caused by an absence of strong Italian leaders and the influence of other European powers on the several Italian courts. The sauces that have come to be known as distinctively Italian are mainly domestic and relatively unrefined in character, based not so much on essences as on whole materials: the purees of tomato fruits and basil leaves, for example. The basic Italian meat sauce, or sugo, is made in the manner of Marin’s 18th-century consommé: meat is slowly cooked to liberate its juices, which are allowed to cook down and brown on the pan bottom; then meat broth is used to redissolve the browned residues, and allowed to concentrate and itself brown: and the process repeated to produce a concentrated flavor. The meat is not discarded, but becomes part of the sauce. Not only Italy but much of the Mediterranean region, including southern France, has been less interested in extracting meat essences than in highlighting and combining flavors.

Sauces in England: Gravies and Condiments According to an 18th-century bon mot attributed to Domenico Caracciolli, with implicit contrast to France: “England has sixty religions and one sauce” — that one sauce being melted butter! And the sharp-toothed Alberto Denti di Pirajno begins the chapter on sauces in his Educated Gastronome (Venice, 1950) with these pointed sentences:

England’s culinary standards were not formed at the Court or in the noble houses; they remained grounded in the domestic habits and economies of the countryside. English cooks ridiculed French cooks for their essences and quintessences. The French gastronome Brillat-Savarin (1755–1826) tells the story of the prince of Soubise being presented with a request from his chef for 50 hams, to be used at one supper party. Accused of thievery, the chef responds that all this meat is essential for the sauces to be made: “Command me, and I can put these fifty hams which seem to bother you into a glass bottle no bigger than your thumb!” The prince is astonished, and won over, by this assertion of the cook’s power to concentrate flavor. By contrast, in her popular 18th-century cookbook, the English writer Hannah Glasse gives several French sauce recipes that require more meat than the meal they will accompany, and then remarks on “the Folly of these fine French Cooks” in running up such huge expenses for so little. Glasse’s principal sauce is “gravy,” made by browning some meat, carrots, onions, several herbs and spices, shaking in some flour, adding water, and stewing. In the 19th century, similarly homely anchovy, oyster, parsley, egg, caper, and butter sauces were popular.

And the Worcestershire sauces and chutneys and ketchups that Denti di Pirajno mocked? These condiments had become a part of English cooking in the 17th century thanks to the commercial activities of the East India Company, which brought back Asian soy and fish sauces — including Indonesian kecap (p. 499) — and pickled fruits and vegetables, all preserved foods with intensified flavors. Many of these preparations are rich in savory amino acids, and the English imitations were often made with similarly savory mushrooms and anchovies. Our familiar tomato ketchup is a sweetened version of salty, vinegary, spicy tomato preserves. So an English contemporary of Carême’s, William Kitchiner, includes a recipe for béchamel in his recipe book, but also presents “Wow Wow Sauce,” which contains parsley, pickled cucumbers or walnuts, butter, flour, broth, vinegar, catsup, and mustard. These strongly flavored concoctions were quick and easy to use, and were evidently enjoyed for their strong contrast to the flavor of the foods they accompanied, not for subtle enhancement.

Modern Sauces: Nouvelle
and Post-Nouvelle

The 20th Century: Nouvelle Cuisine Back in the 18th century, François Marin and his colleagues described their bouillon-based cooking as nouvelle cuisine, or the “new cooking.” In the hands of Carême and Escoffier, that nouvelle cuisine was augmented with a few new sauces and became classic French cooking, the standard throughout the western world for fine dining. In time, the classic system became increasingly rigid and predictable, with most chefs essentially preparing the same standard dishes from the same precooked sauce bases. The 20th century brought a new nouvelle cuisine, along with the New Novel and the New Wave in cinema. In the 1960s a number of well established French chefs, including Paul Bocuse, Michel Guérard, the Troisgros family, and Alain Chapel, led the way in rethinking the French tradition. They asserted the chef’s creative role and the virtues of simplicity, economy, and freshness. Foods were no longer to be distilled into their essences, but were to be presented intact, as themselves.

In 1976, the journalists Henri Gault and Christian Millau published the Ten Commandments of nouvelle cuisine, of which the seventh was: “You shall eliminate brown and white sauces.” The new cooks still thought that, in the words of Michel Guérard, “the great sauces of France must be described as the cornerstones of cuisine,” but they used them more selectively and with restraint. Lighter-flavored veal, chicken, and fish stocks served as poaching and braising liquids; reductions of these were used to give depth to last-minute pan sauces; and sauces in general were thickened less with flour and starch, more often with cream, butter, yogurt and fresh cheese, vegetable purees, and with bubbly foams.

Post-Nouvelle: Diverse and Innovative Sauces At the opening of the 21st century, the classic brown and white sauces have become scarce, so much so that perhaps we’re ready to appreciate their virtues again. Those restaurant and home cooks who do serve time-consuming meat stocks and reductions seldom make them from scratch; these products are well suited to manufacture on an industrial scale, and good versions are available in frozen form. The rich cream and butter sauces popularized by the nouvelle cuisine have become less common; simpler broths, reduced pan deglazings, and vinaigrettes more so. Thanks to the international scope of modern cooking, restaurant diners encounter a wider range of sauces than ever before. Many of them are contrasting purees made from fruits, vegetables, nuts, and spices, or else thinner soy-and fish-based Asian dipping sauces; these are attractive to restaurateurs because they require less time, labor, and often less skill than the classic French sauces. Similarly, home cooks are now likely to buy time-saving and versatile bottled sauces and dressings. And a few inventive chefs are experimenting with unusual tools and materials — among them liquid nitrogen, high-powered pulverizers, thickeners derived from seaweeds and microbes — to make new forms of suspensions, emulsions, foams, and jellies.

The subtleness and delicacy described by I Yin and François Marin are not especially prominent among contemporary sauces. On the other hand, never before in history have we had so many distillations of desire from which to choose!

The Science of Sauces:
Flavor and Consistency

Flavor in Sauces:
Taste and Smell

The primary purpose of a sauce is to provide flavor in the form of a liquid with a pleasing consistency. It’s much easier to generalize about consistency, how it is created, and how it can go wrong, than to generalize about flavor. There are many thousands of different flavor molecules; they can be combined in untold numbers of ways, and different people perceive them differently. Still, it’s useful to keep a few basic facts about flavor in mind when constructing a sauce.

The Nature of Flavor Flavor is mainly a combination of two different sensations, taste and smell. Taste is perceived on the tongue, and comes in five different sensations: saltiness, sweetness, sourness, savoriness, bitterness. The molecules that we taste — salt, sugars, sour acids, savory amino acids, bitter alkaloids — are all easily soluble in water. (The astringent sensation caused by tea and red wine is a form of touch, and the “hot” pungency of mustard is a form of pain. They are not true tastes, but we also perceive them on the tongue and their causes are also water-soluble molecules.) Smell is perceived in the upper nasal region, and comes in thousands of different aromas that we usually describe by the foods they remind us of, fruity or flowery or spicy or herbaceous or meaty. The molecules that we smell are more soluble in fat than in water, and tend to escape from water into the air, where our smell detectors can sniff them.

It can be useful to think of taste as the backbone of a flavor, and smell as its fleshing out. Taste alone is what we experience when we take some food in the mouth and pinch our nostrils shut; smell alone is what we experience when we sniff some food without putting it in the mouth. Neither is fully satisfying on its own. And recent research has shown that taste sensations affect our smell sensations. In a sweet food, the presence of sugar enhances our perception of aromas, and in savory foods, the presence of salt has the same effect.

The Spectrum of Sauce Flavors When considered as carriers of flavor, sauces form a broad spectrum. At one end are simple mixtures that provide a pleasing contrast to the food itself, or add a flavor that it lacks. Melted butter offers a subtle richness, vinaigrette salad dressings and mayonnaise a tart richness, salsas tartness and pungency. At the other end of the spectrum are complex flavor mixtures that fill the mouth and nose with sensations, and provide a rich background into which the flavor of the food itself blends. Among these are the meat-based sauces of the French tradition, whose complexity comes largely from the extraction and concentration of savory amino acids and other taste molecules, and from the generation of meaty aromas by way of the browning reactions between amino acids and sugars (p. 778). Chinese braising liquids based on soy sauce are similarly complex thanks to the cooking and fermentation of the soybeans (p. 496), while the spice blends of India and Thailand and the moles of Mexico typically combine a half dozen or more strongly aromatic and pungent ingredients.

Improving Sauce Flavor Perhaps the most common problem with sauce flavor is that there doesn’t seem to be enough of it, or that “there’s something missing” in it. Perfecting the flavor of any dish is an art that depends on the perceptiveness and skill of the cook, but there are two basic principles that can help anyone analyze and improve a sauce’s flavor.

• Sauces are an accompaniment to a primary food, are eaten in small amounts compared to the primary food, and therefore need to have a concentrated flavor. A spoonful of sauce alone should taste too strong, so that a little sauce on a piece of meat or pasta will taste just right. Thickening agents tend to reduce the flavor of a sauce (p. 596), so it’s important to check and adjust the flavor after thickening.
• A satisfying sauce offers stimulation to most of our chemical senses. A sauce that doesn’t seem quite right is probably deficient in one or more tastes, or doesn’t carry enough aroma. The cook can taste the sauce actively for its saltiness, sweetness, acidity, savoriness, and aroma, and then try to correct the deficiencies while maintaining the overall balance of flavors.

Sauce Consistency

Though the main point of sauces is their flavor, we also enjoy them for their consistency, their feeling in the mouth. And problems with consistency — with the sauce’s physical structure — are far more likely than flavor problems to make a sauce unusable. Curdled or congealed or separated sauces are not pleasant to look at or to feel in the mouth. So it’s good to understand the physical structures of common sauces, how they’re put together and how they’re ruined.

Food Dispersions: Mixtures That Create Texture The base ingredient in nearly all flavorful food liquids is water. That’s because foods themselves are mostly water. Meat juices, vegetable and fruit purees are all obviously watery; cream and mayonnaise and the hot egg sauces less obviously so, but they too are built on water. In each of these preparations, water is the continuous phase: the material that bathes all the other components, the material in which all the other components swim. (The only common exceptions are some vinaigrettes and butter and nut butters, in which fat is the continuous phase.) Those other components are the dispersed phase. The task of giving sauces a desirable consistency is a matter of making the continuous, base phase of water seem less watery, more substantial. The way this is done is to add some nonwatery substance — a dispersed phase — to the water. This substance may be particles of plant or animal tissue, or various molecules, or droplets of oil, or even bubbles of air. And how do the added substances make the water seem more substantial? By obstructing the free movement of the water molecules.

Obstructing the Movement of Water Molecules Individual water molecules are small — just three atoms, H₂O. Left to themselves, they’re very mobile: so water is runny and flows as easily as a stream. (Oil molecules, by contrast, have three chains stuck together, each 14 to 20 atoms long, so they drag against each other and move more slowly. This is why oil is more viscous than water.) But intersperse solid particles or long, tangly molecules, or oil droplets, or air bubbles among the water molecules, and the water molecules can move only a small distance before they collide with one of these foreign, less mobile substances. They’re then able to make only slow progress, so they flow more reluctantly.

Thickening agents in saucemaking are just such obstructing agents. Cooks have traditionally thought of them as binding agents, and this view makes its own kind of sense. The dispersed materials essentially divide the liquid into many small, local masses: and by dividing, they organize and collect it and give it a kind of coherence that it lacked beforehand. Some thickening agents also literally bind water molecules to themselves and so take them out of circulation altogether, and this too has the effect of reducing the fluidity of the continuous phase.

In addition to giving watery fluids a thicker consistency, the substances in the dispersed phase can give them textures of various kinds. Solid particles may make them grainy or smooth, depending on the particle size; oil droplets make them seem creamy; dispersed molecules with a tendency to adhere to each other may make them seem sticky or slimy; air bubbles make them seem light and evanescent.

There are four common ways of thickening watery food juices. Each produces a different kind of physical system, and lends different qualities to the finished sauce.

Cloudy Suspensions: Thickening with Particles Most of our raw ingredients — vegetables, fruits, herbs, meats — are plant or animal tissues built from microscopic cells that are filled with watery fluids. The cells are contained within walls, membranes, or thin sheets of connective tissue. (Dry seeds and spices contain no juices, but are still made up of solid cells and cell walls.) When any of these foods is broken apart into small pieces by being ground in a mortar or pulverized in a blender, they are turned inside out, so the fluids form a continuous phase that contains fragments of the solid cell walls and connective tissue. These fragments obstruct and bind the water molecules, and thus thicken the consistency of the mixture. Such a mixture of a fluid and solid particles is called a suspension: the particles are suspended in the fluid. Sauces made from pureed foods are suspensions.

The texture of a suspension depends on the size of its particles. The smaller the particles, the less noticeable they are to the tongue, and the smoother the texture. Also, the smaller the particles are, the more of them there are to do the obstructing and the more surface area they have to take up a layer of water molecules: and so the thicker the consistency they produce. Suspensions are always opaque, because the solid particles are large enough to block the passage of light rays and either absorb them or bounce them back toward their source. Because the particles and water are very different materials, suspensions tend to settle and separate into thin fluid and concentrated particles. Cooks work to prevent separation by reducing the volume of the continuous phase (draining off or boiling away excess water), or by augmenting the dispersed phase (adding starch or other long molecules or fat droplets).

Nut butters and chocolate are suspensions of solid seed particles not in water, but in oils and fats.

Thickening a liquid with food particles. In a suspension, microscopic chunks of plant or animal tissue are suspended in liquid, and give the impression of thickness by interfering with the liquid’s flow.

Clear Dispersions and Gels: Thickening with Molecules A single microscopic fragment of a tomato cell wall or muscle fiber is built up of many thousands of submicroscopic molecules. Not all of the large molecules in those fragments can be teased away from each other so that they are individually dispersed in water. But those that can be extracted in this way — starch, pectins, such proteins as gelatin — are very useful thickening agents. Because single molecules are so much smaller and lighter than intact starch granules and cell fragments, they don’t settle out and separate. And they are too small and too widely separated to block the passage of light rays: so unlike suspensions, molecular dispersions are usually translucent and glassy-looking. In general, the longer the molecule, the better it is at obstructing water movement, because long molecules more readily get tangled up in each other. So a small quantity of long amylose starch molecules will do the same thickening job as a large quantity of short amylopectin (p. 611), and long gelatin molecules thicken more efficiently than short ones. Thickening with molecules often requires heat, either to liberate the molecules from the larger structures — starch molecules from their granules, gelatin molecules from meat connective tissue — or to shake out compactly folded molecules — egg proteins — into their long, extended, tangly form.

Solid Dispersions: Jellies When the water phase of a food fluid has enough thickening molecules dissolved in it, and the fluid is left undisturbed and allowed to cool, those molecules can bond to each other and form a loose but continuous tangle or network that permeates the fluid, with the water immobilized in pockets between the network molecules. Such a network thickens the fluid to the point that it becomes a very moist solid, or a gel. It’s possible to make a solid — if wobbly — jelly that is 99% water and just 1% gelatin. If the gel is made from dissolved molecules, then it will be translucent, like the dispersion from which it is formed. Familiar examples are savory jellies made from gelatin and sweet jellies made from fruit pectin. If the solution also contains particles — the remains of starch granules, for example — then the jelly will be opaque.

Thickening a liquid with long food molecules. Dissolved molecules of plant starch or animal gelatin get tangled up with each other and impede the flow of the liquid.

Emulsions: Thickening with Droplets Thanks to their very different structures and properties, water molecules and oil molecules don’t mix evenly with each other(p. 797). Neither can dissolve in the other. If we use a whisk or blender to force a small portion of oil to mix into a larger one of water, the two form a milky, thick fluid. Both the milkiness and the thickness are caused by small droplets of oil, which block light rays and the free movement of water molecules. The oil droplets thus behave much as the solid particles in a suspension do. Such a mixture of two incompatible liquids, with droplets of one liquid dispersed in a continuous phase of the other, is called an emulsion. The term comes from the Latin word for “milk,” which is just such a mixture (p. 17).

Emulsifiers In addition to the two incompatible liquids, a successful emulsion requires a third ingredient: an emulsifier. An emulsifier is a substance of some kind that coats the oil droplets and prevents them from coalescing with each other. Several different materials can serve this function, including proteins, cell-wall fragments, and a group of hybrid molecules (for example, egg-yolk lecithin) that have an oil-like end and a water-soluble end (p. 802). To make an emulsified sauce, we add oil to a mixture of water and emulsifiers (egg yolk, ground herbs or spices), and break the oil up into microscopic droplets, which the emulsifiers immediately coat and stabilize. Or we can begin with a premade emulsion. Cream is an especially robust and versatile base for emulsified sauces.

Foams: Thickening with Bubbles At first it seems surprising that a fluid can be thickened by adding air to it. Air is the opposite of substantial! Yet think of the foams on an espresso coffee or a glass of beer: they all have enough body to hold their shape when scooped with a spoon. Similarly, a pancake batter gets noticeably thicker if you stir the chemical leavening in last. In a fluid, air bubbles have much the same effect as solid particles: they interrupt the mass of water molecules and obstruct the water’s flow from one place to another. The disadvantage of foams is that they are fragile and evanescent. The force of gravity unceasingly drains fluid from the bubble walls, and when the walls get just a few molecules thick, they break, the bubbles pop, and the foam collapses. This outcome can be delayed in a couple of ways. The cook can thicken the fluid with truly substantial particles or molecules (oil droplets, egg proteins) to slow its drainage from the bubble cell walls, or include emulsifiers (egg-yolk lecithin) that stabilize the bubble structure itself. On the other hand, the very delicacy and evanescence of unreinforced foams is a part of their appeal. Such foams must be prepared at the last minute and savored as they disappear.

Thickening a liquid with oil droplets and air bubbles. These tiny spheres act much as solid food particles do, interfering with the flow of the liquid surrounding them.

Real Sauces: Multiple Thickeners The sauces that cooks actually make are seldom simple suspensions, molecular dispersions, emulsions, or foams. They’re usually a combination of two or more. Purees usually contain both suspended particles and dispersed molecules, starch-thickened sauces contain both dispersed molecules and remnants of the granules, emulsified sauces include proteins and particles from milk or eggs or spices. Cooks often thicken and enrich sauces of all kinds at the last minute by melting a piece of butter into it or stirring in a spoonful of cream, thus making them in part a milkfat emulsion. Such complexity of the dispersed phase may well make sauce texture more subtle and intriguing.

The Influence of Consistency on Flavor

Thickeners Reduce Flavor Intensity In general, the components of a sauce that create its consistency have little or no flavor of their own. They therefore only dilute whatever flavors the sauce has. Thickening agents also actively reduce the effectiveness of the flavor molecules in the sauce. They bind some of those molecules so that our palate never senses them, and they slow their movement from the sauce into our taste buds or nasal passages. Because aroma molecules tend to be more fat soluble than water soluble, fat in a sauce hangs onto aroma molecules and decreases aromatic intensity. Amylose starch molecules trap aroma molecules (the aroma molecules in turn make the starch molecules more likely to bond to each other into light-scattering, milky aggregates). And wheat flour binds more sodium than pure starches, so flour-thickened preparations require more added salt than starch-thickened sauces.

As a general rule, then, a thin sauce will have a more intense and immediate flavor than the same sauce with thickeners added. But the thickened sauce will release its flavor more gradually and persistently. Each effect has its uses.

Many sauces can be thickened not just by adding thickeners, but by removing some of the continuous phase — boiling off water — so that the thickeners already present in the sauce become more concentrated. This technique doesn’t diminish flavor, because whatever flavor the sauce’s particles and molecules can bind have already been bound. And in fact it can intensify flavor, because the concentration of flavor molecules may increase just as the thickeners’ concentration does.

The Importance of Salt Recent research has uncovered intriguing indications that thickeners reduce our perception of aroma in part because they reduce our perception of saltiness. Various long-chain carbohydrates, including starch, first reduce the apparent saltiness of the sauce, either by binding sodium ions to themselves or by adding another sensation (viscosity) for the brain to attend to. Then this reduced saltiness reduces the apparent aroma intensity — despite the fact that the same number of aroma molecules are flowing out of the sauce and across the smell receptors in our nose. The practical significance of this finding is that thickening a sauce with flour or starch diminishes its overall flavor, and that both taste and aroma can be restored to some extent by the simple addition of more salt.

Sauces Thickened
with Gelatin and
Other Proteins

If we gently heat a piece of meat or fish alone in a pan, it releases flavorful juices. Normally we make the pan hot enough to evaporate the water the moment it comes out, so that the flavor molecules become concentrated on the meat and pan surfaces, and react with each other to form brown pigments and a host of new flavor molecules (p. 778). But if the juices remain juices, they constitute a very basic sauce, a product of the meat that can be added back to moisten and flavor the mass of coagulated muscle protein from which they’ve been squeezed. The problem is that the meat or fish only gives up a small amount of juice compared to the solid mass. To satisfy fully our appetite for those juices, cooks have invented methods for making meat and fish sauces for their own sake, and in any quantity. The main thickening agent in these sauces is gelatin, an unusual protein that cooking releases from the meat and fish. Cooks also use other animal proteins to thicken sauces, but their behavior is very different and more problematic, as we’ll see (p. 603).

The Uniqueness of Gelatin

Gelatin is a protein, but it’s unlike the other proteins that the cook works with. Nearly all food proteins respond to the heat of cooking by unfolding, bonding permanently to each other, and coagulating into a firm, solid mass. It turns out that gelatin molecules can’t easily form permanent bonds with each other, due to their particular chemical makeup. So heat simply causes them to shake loose from the weak, temporary bonds that hold them together, and disperses them in water. Because gelatin molecules are very long and get tangled up with each other, they give the mixture a definite body, and can even set it into a solid gel (p. 605). However, gelatin is relatively inefficient at thickening. Its molecules are very flexible, while those of starch and other carbohydrates are rigid and better at interfering with the movement of water and each other. This is one reason why gelatin-thickened sauces are usually augmented with starch. A sauce that contains only gelatin requires a large concentration, 10% or more, to have real weight. But at that concentration, the sauce is quick to congeal on a cooling plate, and it can also cause the teeth to stick together (gelatin makes an excellent glue!).

Gelatin Comes from Collagen Free gelatin molecules don’t exist in meat and fish. They’re woven tightly together to form the fibrous connective-tissue protein called collagen (p. 130), which gives mechanical strength to muscles, tendons, skin, and bones. Single gelatin molecules are chains of around 1,000 amino acids. Thanks to the repeating pattern of their amino acids, three gelatin molecules naturally fit alongside each other and form weak, reversible bonds that arrange the three molecules in the form of a triple helix. Many triple helixes then become cross-linked to each other to form the strong, rope-like fibers of collagen.

Cooks generate gelatin from collagen by using heat to dismantle the collagen fibers. For the muscles of land animals, it takes a temperature of around 140ºF/60ºC to agitate the muscle molecules enough to break the weak bonds of the triple helix. The orderly structure of the collagen fibers then collapses and the fibers shrink, thus squeezing juices from the muscle fibers. Some of the juices bathe the fibers, and single gelatin molecules or small aggregates may disperse into the juice. The higher the meat temperature goes, the more gelatin becomes dispersed. However, many of the collagen fibers remain intact thanks to the strong cross-linking bonds. The older the animal and the more work its muscles do, the more strongly cross-linked its collagen fibers are.

Extracting Gelatin
and Flavor from Meats

The muscles that make up meat are mainly water and the protein fibers that do the work of contraction, which are not dispersable in water. The soluble and dispersable materials in muscle include about 1% by weight of collagen, 5% other cell proteins, 2% amino acids and other savory molecules, 1% sugars and other carbohydrates, and 1% minerals, mainly phosphorus and potassium. Bones are around 20% collagen, pig skin around 30%, and cartilaginous veal knuckles up to 40%. Bones and skin are thus much better sources of gelatin and thickening power than meat. However, they carry only a small fraction of the other soluble molecules that provide flavor. To make sauces with good meat flavor, it’s meat that must be extracted, not bones or skin.

When meat is thoroughly cooked, it releases about 40% of its weight in juice, and the flow of juice pretty much ends when the tissue reaches 160ºF/70ºC. Most of the juice is water, and the rest the soluble molecules carried in the water. If meat is cooked in water, then gelatin can be freed from the connective tissue and extracted over a long period of time. When cooks make stocks, extraction times range from less than an hour for fish, to a few hours for chicken or veal stocks, to a day for beef. Optimum extraction times depend on the size of the bones and meat pieces, and on the age of the animal; the more cross-linked collagen of a steer takes longer to free than the collagen from a veal calf. At long extraction times, the gelatin molecules that have already been dissolved are gradually broken down into smaller pieces that are less efficient thickeners.

Meat Stocks and Sauces

There are several general strategies for making meat and fish sauces. The simplest of them center on the juices produced when the meat for the final dish is cooked, which can be flavored and/or thickened at the last minute with purees, emulsions, or a starch-based mixture. In the more versatile system developed by French cooks, one begins by making a water extract of meat and bones ahead of time, and then uses that stock to cook the final dish, or concentrates it to make intensely flavored, full-bodied sauces. These stocks and concentrates used to be the heart of restaurant cooking. They’re less important now, but still represent the state of the art in meat sauces.

Collagen and gelatin. Collagen molecules (left) contribute mechanical strength to connective tissue and bone in animal muscles. They are made up of three individual protein chains wound closely together into a helix to make a rope-like fiber. When heated in water, the individual protein chains come apart (right) and dissolve into the water. The unwound, separate chains are what we call gelatin.

The Choice of Ingredients The aim in making meat stock is to produce a full-flavored liquid with enough gelatin that it will also become full-bodied when reduced. Meat is an expensive ingredient, an excellent source of flavor, and a modest source of gelatin. Bones and skins are less expensive, poor sources of flavor, but excellent sources of gelatin. So the most flavorful and expensive stocks are made with meat, the fullest bodied and cheapest with bones and pork skin, and everyday stocks with some of each. Beef and chicken stocks taste distinctly of their respective meats, while veal bones and meat are valued for their more neutral character, as well as their higher yield of soluble gelatin. Cartilaginous veal knuckles and feet give especially large amounts. Typically, the meat and bones are cooked in between one and two times their weight in water (1–2 quarts or liters per 2 lb/1 kg solids), and yield about half their weight in stock, thanks to gradual evaporation during cooking. The smaller the pieces into which they’re cut, the more quickly their contents can be extracted in the water.

In order to round out the flavor of a stock, cooks usually cook the meat and bones along with aromatic vegetables — celery, carrots, onions — a packet of herbs, and sometimes wine. Carrots and onions contribute sweetness as well as aroma, wine tartness and savoriness. Salt is never added at this stage, because the meats and vegetables release some, and it becomes concentrated as the stock reduces.

Cooking the Stock A classic meat stock should be as clear as possible, so that it can be made into soup broths and aspics that will be attractive to the eye. Many of the details of stock making have to do with removing impurities, especially the soluble cell proteins that coagulate into unsightly gray particles.

The bones and often meat as well (and skin, if any) are first washed thoroughly. To make a light stock, they are then put in a pot of cold water that is brought to the boil; they’re then removed from the pot and rinsed. This blanching step removes surface impurities and coagulates surface proteins on the bones and meat so that they won’t cloud the cooking liquid. To make a dark stock for brown sauces, the bones and meat are first roasted in a hot oven to produce color and a more intense roasted-meat flavor with the Maillard reactions between proteins and carbohydrates. This process also coagulates the surface proteins and makes blanching unnecessary.

The Importance of a Cold Start and Uncovered, Slow Heating After the blanching or browning, the meat solids are started in an uncovered pot of cold water, which the cook brings slowly to a gentle simmer and keeps there, regularly skimming off the fat and scum that accumulate at the surface. The cold start and slow heating allow the soluble proteins to escape the solids and coagulate slowly, forming large aggregates that either rise to the surface and are easily skimmed off, or settle onto the sides and bottom. A hot start produces many separate and tiny protein particles that remain suspended and cloud the stock; and a boil churns particles and fat droplets into a cloudy suspension and emulsion. The pot is left uncovered for several reasons. Because this allows water to evaporate and cool the surface, it makes it less likely that the stock will boil. It also dehydrates the surface scum, which becomes more insoluble and easier to skim. And it starts the process of concentration that will give the stock a more intense flavor.

Single and Double Stocks After the scum has mostly stopped forming, the vegetables, herbs, and wine are added and the cooking is continued at a gentle simmer until most of the flavor and gelatin have been extracted from the solids. The liquid is strained through cheesecloth or a metal strainer without pressing on the solids, which would extract cloudy particles. It’s then thoroughly chilled, and the solidified fat removed from the surface. (If the cook doesn’t have the time to chill the stock, he can soak away much of the fat from the surface with cloth or paper towels or specially designed plastic blotters.) The stock is now ready to use as an ingredient, to make braised and stewed meats and meat soups, or as a savory cooking liquid for vegetables; or it may be reduced for use in a sauce. The cook may also use stock to extract a new batch of meat and bones and produce the especially flavorful, highly prized — and expensive — double stock. (Double stock can in turn be combined with more fresh meat and bones to make a triple stock.)

Because a standard kitchen extraction of eight hours releases only about 20% of the gelatin in beef bones, the bones may be extracted for a second time, for a total of up to 24 hours. The resulting liquid can then be used to start the next fresh extraction of meat and bones.

Concentrating Meat Stocks: Glace and Demi-glace Slowly simmered until it’s reduced to a tenth its original volume, stock becomes glace de viande, literally “meat ice” or “meat glass,” which cools to a stiff, clear jelly. Glace has a thick, syrupy, sticky consistency thanks to its high gelatin content, about 25%, an intensely savory taste thanks to the concentrated amino acids, and a rounded, mellow, but somewhat flat aroma thanks to the long hours during which volatile molecules have been boiled off or reacted with each other. Meat glace is used in small quantities to lend flavor and body to sauces. Intermediate between stock and glace is demi-glace or “half-glace,” which is stock simmered down to 25–40% of its original volume, often with some tomato puree or paste to add flavor and color, and with some flour or starch to supplement its lower gelatin content (10–15%). The tomato particles and flour gluten proteins cloud the stock and are removed by skimming the stock as it reduces, and then by a final straining. The starch in demi-glace, around 3–5% of its final weight, is largely an economy measure — it gives a greater thickness with less stock reduction and loss of volume to evaporation — but it also has the advantage of sparing some of the stock’s flavor from being boiled off, and avoiding the sticky consistency of very concentrated gelatin.

Demi-glace is the base for many classic French brown sauces, which are given particular flavors and nuances with the addition of various other ingredients (meats, vegetables, herbs, wine) and final enriching thickeners (butter, cream). Because they’re versatile but tedious to prepare, demi-glace and glace are manufactured and widely available in frozen form.

Consommé and Clarification with Egg Whites One of the most remarkable soups is consommé, an intensely flavored, amber-colored, clear liquid with a distinct but delicate body. (The name comes from the French for “to consume,” “to use up,” and referred to the medieval practice of cooking the meat broth down until it reached the right consistency.) It is made by preparing a basic stock mainly from meat, not flavor-poor bones or skin, and then clarifying it while simultaneously extracting a second batch of meat and vegetables. It’s a kind of double stock made expressly for soup; as much as a pound/0.5 kg of meat may go into producing one serving.

The clarification of consommé is accomplished by stirring finely chopped meat and vegetables into the cold stock along with several lightly whisked egg whites. The mixture is then brought slowly to the simmer, and kept there for around an hour. As the stock heats up, the abundant egg white proteins begin to coagulate into a fine cheesecloth-like network, and essentially strain the liquid from within. Soluble proteins from the fresh batch of meat help produce large protein particles that are easily trapped by the egg-white network. Gradually the protein mesh rises to the top of the pot to form a “raft,” which continues to collect particles brought to the surface by convection in the liquid. When the cooking is done, the raft is skimmed off and any remaining particles are removed by a final straining. The resulting liquid is very clear. Clarification with egg whites does remove both flavor molecules and some gelatin from the stock, which is why the cook supplies fresh meat and vegetables during the clarification.

Commercial Meat Extracts
and Sauce Bases

These days many restaurants and home cooks rely on commercial meat extracts and bases for making their sauces and soups. The pioneer of mass-produced meat extracts was Justus von Liebig, inventor of the mistaken theory that searing meat seals in the juices (p. 161), who was motivated by the equally mistaken belief that the soluble substances in meat contain most of its nutritional value. However, they do contain much of its savory flavor. Today, meat extracts are made by simmering meat scraps and/or bones in water, then clarifying the stock and evaporating off more than 90% of the water. The initial stock is more than 90% water and 3–4% dissolved meat components; the finished extract is a viscous material that is about 20% water, 50% amino acids, peptides, gelatin, and related molecules, 20% minerals, mainly phosphorus and potassium, and 5% salt. (There are also less concentrated fluid extracts, and solid bouillon cubes that have various natural and artificial flavors added.) Because gelatin would make such concentrated material too thick to work with, manufacturers intentionally break it down into smaller molecules by extending the initial cooking by several hours, and by pressure-cooking the clarified stock (at around 275ºF/135ºC for 6–8 minutes; this step also coagulates the remaining soluble proteins). In order to limit browning reactions and keep the extract light in both color and roasted flavor, much of the water evaporation is done at temperatures below 170ºF/75ºC.

Manufacturers now also produce more conventional sauce bases with their gelatin intact. These are often sold in the form of demi-glace or glace de viande.

Cooks can improve the flavor of commercial meat extracts and canned broths by cooking them briefly with herbs and/or diced aromatic vegetables. This fills out the extract’s aroma, which is generically meaty to begin with and depleted during the concentration process.

Fish and Shellfish Stocks
and Sauces

Like mammals and birds, fish have bones and skin rich in connective tissue. But thanks to the cold environment in which fish bodies function (p. 189), their collagen differs from mammal and bird collagens. Fish collagen is less cross-linked, and so melts and dissolves at much lower temperatures. The collagen and gelatin of warm-water fish like tilapia melt at around 77ºF/25ºC, that of cold-water cod around 50ºF/10ºC. So we can extract fish gelatin at cooking temperatures far below the boil, and in relatively short times. The collagen of squid and octopus is more cross-linked than fish collagen, so these molluscs require more prolonged heating at 180ºF/80ºC to give up much of their gelatin. Most cooks recommend cooking fish stocks for less than an hour so as to avoid making the stock cloudy and chalky with calcium salts from the dis-integrating bones. Another reason for short and gentle extractions is that fish gelatins are relatively fragile and more readily break down into small pieces when cooked. And because they associate more loosely with each other, they form delicate gels that melt far below mouth temperature, at 70ºF/20ºC and lower.

Because fish flavor deteriorates quickly, it’s important that fish stock or fumet be made with very fresh ingredients. Whole fish, bones, and skin should be thoroughly cleaned and rinsed, and the blood-rich, very perishable gills discarded. Cooks often briefly cook the ingredients in butter to develop the flavor. A gelatin-bodied sauce can be made from the cooking liquid of poached or steamed fish, since even brief cooking will extract flavor and gelatin into the liquid. The traditional cooking liquid for fish is a court bouillon or “quick bouillon” made by briefly cooking water, salt, wine, and aromatics together (p. 215).

The bony shells of crustaceans don’t contain collagen, so cooking them in water won’t give body to the extract. In fact crustacean shells are normally extracted in butter or oil, since their pigments and flavors are more soluble in fat than in water(p. 220).

Other Protein Thickeners

Gelatin is the easiest, most forgiving protein any cook deals with. Heat it up with water and its molecules let go of each other and become dispersed among the water molecules; cool it and they rebond to each other; heat it again and they disperse again. Nearly all other proteins in animals and plants behave in exactly the opposite way: heat causes them to unfold from their normally compact shape, become entangled, and form strong bonds with each other, so that they coagulate permanently and irreversibly into a firm solid. Thus liquid eggs solidify, pliable muscle tissue becomes stiff meat, and milk curdles. Of course a solid piece of coagulated protein can’t be a sauce. But it’s possible to control protein coagulation so that it can give body to sauces.

Protein thickening and curdling. Two possible outcomes of heating egg proteins, which start out folded in compact shapes (left). If conditions favor their unfolding, they form a loose network of long chains (center) and thicken the sauce. If heated excessively, the chains aggregate and coagulate in compact clumps (right) that give the sauce a curdled consistency and appearance.

Careful Temperature Control Cooks first make the flavorful but thin liquid that will be the bulk of the sauce and then add a source of finely suspended proteins. An example is the fricassee, in which the liquid is the stock in which chicken or another meat has been cooked, and the protein source is egg yolks. The mixture is then heated gently. At the point that the proteins unfold and begin to tangle — but before they form strong bonds — the sauce thickens noticeably: it clings to a spoon rather than running off. The attentive cook immediately takes the sauce from the heat and stirs, thus preventing the proteins from forming very many strong bonds, until the sauce cools enough to prevent further bonding. If the sauce gets too hot and the proteins do form strong bonds, they clot together into dense particles, and the sauce becomes grainy and thins out again. Most animal proteins coagulate beginning around 140ºF/60ºC, but this critical point can vary, so there’s no substitute for careful monitoring of the sauce’s consistency. Once the sauce has thickened, careful straining can remove the few particles that may have formed.

In all protein-thickened sauces, the cook must take care when mixing the hot sauce with the cool thickener. It’s always safest to stir some of the sauce into the thickener, thus heating the thickener gently and diluting it, and then add that mixture to the rest of the sauce. If the thickener goes directly into the sauce, then some of the thickener will get instantly overheated and coagulate into grainy particles. Cooks sometimes work pastes of liver or shellfish organs into butter and then chill the mix. When a chunk of the mix is added to the sauce, the butter melts and slowly releases the thickener into the sauce, while making it somewhat harder for the thickener proteins to bond to each other and coagulate. The inclusion of flour or starch can protect sauce proteins from coagulating; the long starch molecules get in the way of the proteins and prevent them from forming many strong bonds with each other.

If you do overcook a protein-thickened sauce and it separates into thin liquid and grainy particles, you can salvage it by remixing the sauce in a blender, straining it of any remaining coarse particles, and if necessary rethickening it with whatever materials are handy (egg yolks, flour, or starch).

Egg Yolks Egg yolks are the most efficient protein thickeners, in part because they are so concentrated: egg yolks are only 50% water and 16% protein. They are also the handiest, being a common, inexpensive ingredient, and their proteins are already finely dispersed in a rich, creamy fluid. They’re mainly used to thicken light-colored white sauces, blanquettes, and fricassees. Yolk-thickened sauces can be brought to the boil as long as they’re also partly thickened by starch.

Sabayon sauces are also partly thickened by the coagulation of yolk proteins(p. 639).

Liver Liver is a flavorful thickener, but has the disadvantage of requiring disintegration before it can be used. The coagulable proteins are concentrated inside its cells, so the cook must break the cells open by pounding the tissue, and then strain away the particles of connective tissue that hold the cells together.

Blood Blood is the traditional thickening agent in coq au vin, the French rooster in wine sauce, and in braises of game animals (civets). It’s about 80% water and 17% protein, and consists of two phases: the various cells, including the red cells colored by hemoglobin, and the fluid plasma in which the cells float. The plasma makes up about two thirds of cattle and pig blood and contains dispersed proteins, about 7% by weight. Albumin is the protein that causes blood to thicken when heated above 167ºF/75ºC .

Shellfish Organs The liver and eggs of crustaceans, and the sexual tissues of sea urchins have the same advantages and disadvantages as liver, and thicken and coagulate at much lower temperatures. They should be added carefully to a sauce that has first been allowed to cool well below the boil.

Cheese and Yogurt These cultured milk products differ from the other protein thickeners in that their casein proteins have already been coagulated by enzyme activity and/or acidity. They’re thus unable to develop a new thickness by being heated with a sauce. Instead, they lend their own thickness as they’re mixed into the sauce. They’re best subjected to only moderate heat, since temperatures approaching the boil can cause curdling. Yogurt is a more effective thickener if it has been drained of its watery whey. The best cheeses for thickening have a creamy consistency themselves, an indication that the protein network has been broken down into small, easily dispersed pieces; more intact casein fibers can form stringy aggregates (p. 65). Most cheeses are a concentrated source of fat, emulsified droplets of which also contribute body.

Almond Milk This water extract of soaked ground almonds contains a significant amount of protein that causes the liquid to thicken when heated or acidified(p. 504).

Solid Sauces: Gelatin Jellies
and Carbohydrate Jellies

When a meat or fish stock is allowed to cool to room temperature, it may set into a fragile solid, or gel. This behavior can be undesirable, for example when it causes some sauce to congeal on the plate. But cooks also exploit it to make delightful jellies, a sort of solid sauce. A gel forms when the gelatin concentration is sufficiently high, around 1% or more of the stock’s total weight. At these concentrations, there are enough gelatin molecules in the stock that their long chains can overlap with each other to form a continuous network throughout the stock. As the hot stock cools down to the melting temperature of gelatin, around 100ºF/40ºC, the extended gelatin chains begin to assume the coiled shape that they had in the original triple helix of the collagen fibers (p. 597). And when coils on different molecules approach each other, they nest closely alongside each other and bond to form new double and triple helixes. These reassembled collagen junctions give some rigidity to the network of gelatin molecules, and they and the water molecules they surround can no longer flow freely: so the liquid turns into a solid. A 1% gelatin gel is fragile and quivery and breaks easily when handled; the more familiar and robust dessert jellies made with commercial gelatin are usually 3% gelatin or more. The higher the proportion of gelatin, the more firm and rubbery the gel is.

Jellies are remarkable in two ways. At their best they are translucent, glistening, beautiful on their own or as settings for the foods embedded in them. And the temperature at which the gelatin junctions are shaken apart is right around body temperature: so gelatin gels melt effortlessly in the mouth to a full-bodied fluid. They bathe the mouth in sauce. No other thickener has this quality.

Jelly Consistency

The firmness or strength of a gelatin gel, and therefore its tolerance of handling and its texture in the mouth, depends on several factors: the gelatin molecules themselves, the presence of other ingredients, and the way in which the mixture is cooled.

Gelatin Quality and Concentration The most important influence on the texture of a jelly is the concentration and quality of its gelatin. Gelatin is a highly variable material. Even manufactured gelatin (below) is only 60–70% intact, full-length gelatin molecules; the remainder consists of smaller pieces that are less efficient thickeners. The gelatin in a stock is especially unpredictable, since meat and bones vary in their collagen content, and long cooking causes progressive breakdown of the gelatin chains. The best way to assess gel strength is to cool a spoonful of the liquid in a bowl resting in ice water, see if the liquid sets, and how firm the gel is. A liquid lacking in firmness can be reduced further to concentrate the gelatin, or it can be supplemented with a small amount of pure gelatin.

How gelatin turns a liquid into a solid. When the gelatin solution is hot (left), the water and protein molecules are in constant, forceful movement. As the solution cools and the molecules move more gently, the proteins naturally begin to form little regions of collagen-like helical association (right). These “junctions” gradually form a continuous meshwork of gelatin molecules that traps the liquid in its interstices, preventing any noticeable flow. The solution has become a solid gel.

Additional Ingredients Other common ingredients have various effects on gel strength when included in a jelly.

• Salt lowers gel strength by interfering with gelatin bonding.
• Sugars (except for fructose) increase gel strength by attracting water molecules away from the gelatin molecules.
• Milk increases gel strength.
• Alcohol increases gel strength until it becomes 30 to 50% of the gel, when it will cause the gelatin to precipitate into solid particles.
• Acids — vinegar, fruit juices, wine — with a pH below 4 produce a weaker jelly by increasing repulsive electrical charges on the gelatin molecules.

The gel-weakening effects of salt and acids can be compensated for by increasing the gelatin concentration.

Both strongly acid ingredients and the tannins in tea or red wine can cloud a jelly, the acids by precipitating proteins in a meat or fish stock into tiny particles, and the tannins by binding to and precipitating the gelatin molecules themselves. These ingredients are best cooked briefly with the gelatin solution so that it can be strained or clarified before setting.

A number of fruits — papaya, pineapple, melons, and kiwi among them — contain protein-digesting enzymes that break gelatin chains into short pieces and thus prevent them from setting into a gel at all. They and their juices can be made into a jelly only after a brief cooking to inactivate the enzymes.

Cooling Temperatures The temperature at which the gel forms and ages affects its texture. When “snap-chilled” in the refrigerator, the gelatin molecules are immobilized in place and bond to each other quickly and randomly, so the bonds and the structure of the network are relatively weak. When allowed to set slowly at room temperature, the gelatin molecules have time to move around and form more regular helix junctions, so once it forms, the network is more firm and stable. In practice, jellies should be set in the refrigerator to minimize the growth of bacteria. Gelatin bonds continue to form slowly in the solid jelly, so snap-chilled jellies become as firm as slow-chilled jellies after a few days.

Jellies from Meat
and Fish: Aspics

Meat and fish jellies go back to the Middle Ages (p. 584), and are still delightful showpieces. They’re made much as consommé is, ideally from a flavorful meat stock — often cooked with a veal foot to provide enough gelatin — or from a double fish stock. The stocks are clarified with egg whites and chopped meat or fish, then filled and flavored just before they set. Aspics should be firm enough to be cut as necessary, but quivery and tender in the mouth, not rubbery. When made to coat a terrine or whole portion of meat, or to bind chopped meat together, they must be firmer, around 10–15% gelatin, so that they don’t run off the food or crumble. Fish jellies and aspics are especially delicate due to the low melting temperature of fish gelatin; they and their plates should be kept distinctly cold to prevent premature melting. A homely version of the meat aspic is boeuf à la mode, a pot roast braised in stock and wine along with a veal foot, then sliced and embedded in the strained jelly made by the cooking liquid. Chauds-froids are meat or fish jellies that include cream.

Other Jellies and Gelées;
Manufactured Gelatins

The first jellies were meat and fish dishes, but cooks soon began to use animal gelatins to set other ingredients into pleasing solids, especially creams and fruit juices, and prepared gelatin became a standard ingredient for the pastry cook, who also uses it to give a melting firmness to some mousses, whipped creams, and pastry creams. The most familiar jellies in the United States today, both made from manufactured gelatin powders, are sweet, fruit-flavored, fluorescently colored desserts, and “shooters” fortified with vodka and other spirits. More refined preparations, often named by the French gelée, take advantage of the fact that other ingredients can be added at the last minute when the mix is barely warm and about to set, so fresh and delicate flavors can be preserved in the jelly: such things as champagne or the “water” from a seeded tomato.

Gelatin Production Most manufactured gelatin in the United States and Europe comes from pigskin, though some is also made from cattle skins and from bones. Industrial extraction is far more efficient and gentler on the gelatin chains than kitchen extractions. The pigskins are soaked in dilute acid for 18–24 hours to break the collagen’s cross-linking bonds, and then are extracted in several changes in water, beginning at just 130ºF/55ºC, and ending around 195ºF/90ºC. The low-temperature extracts contain the most intact gelatin molecules, produce the strongest gels, and are the lightest in color; higher temperatures damage more gelatin chains and cause a yellow discoloration. The extracts are then filtered, purified, their pH adjusted to 5.5, evaporated, sterilized, and dried into sheets or granules that are 85–90% gelatin, 8–15% water, 1–2% salts, and 1% glucose. Gelatin quality is sometimes indicated by a “Bloom” number (named for Oscar Bloom, inventor of the measuring device), with high numbers (250) indicating high gelling power.

Types of Gelatin Gelatin is sold in several different forms. Granulated gelatin and sheet gelatin are given an initial soaking in cold water so that the solid gelatin network can absorb moisture and dissolve readily when warm liquid is added. If added to the warm liquid directly, the outer layers of the solid granules can become gluey and stick neighboring granules together, though even these clusters eventually disperse. Sheets with their small surface area introduce less air into the liquid, which can be an advantage when the cook wants great clarity in the jelly. There is also an “instant” gelatin that is manufactured by drying the extract rapidly before the gelatin chains can form junctions, so it disperses directly in warm liquid. And hydrolyzed gelatins have been intentionally broken into chains too short to form a gel; they’re used in food manufacturing as an emulsifying agent (p. 627).

The standard proportion advised by dessert gelatin packages is one 7-gm package per cup/240 ml, or about a 3% solution; 2% and 1% solutions are progressively more tender.

Carbohydrate Gelling
agents: Agar, Carrageenan,
Alginates

Gelatin isn’t the only ingredient that cooks have at their disposal for turning a flavorful liquid into an intriguing solid. Starch gels give us various pie fillings and the candy called Turkish Delight, and pectin gels the many fruit jellies and jams (p. 296). Along the seacoasts of the world, cooks found long ago that various seaweeds release a viscous substance into hot water that forms a gel when the water cools. These substances are not proteins like gelatin, but unusual carbohydrates with some unusual and useful properties. Food manufacturers use them to make gels and to stabilize emulsions (cream and ice cream, for example).

Agar Agar, a shortened version of the Malay agar agar, is a mixture of several different carbohydrates and other materials that has long been extracted from several genera of red algae (p. 341). It’s now manufactured by boiling the seaweeds, filtering the liquid, and freeze-drying it in the form of sticks or strands, which are readily available in Asian groceries. The solid pieces of agar can be eaten uncooked as a chewy ingredient in cold salads, soaked and cut into bite-sized pieces. In China agar is made into an unflavored gel that’s sliced and served in a complex sauce; it’s also used to gel flavorful mixtures of fruit juice and sugar, and stews of meats, fish, or vegetables. In Japan agar is made into jellied sweets.

Agar forms gels at even lower concentrations than gelatin does, less than 1% by weight. An agar jelly is somewhat opaque, and has a more crumbly texture than a gelatin jelly. To make an agar jelly, the dried agar is soaked in cold water, then heated to the boil to fully dissolve the carbohydrate chains, mixed with the other ingredients, and the mixture strained and cooled until it sets, at around 110ºF/38ºC. But where a gelatin gel sets and remelts at around the same temperature, an agar gel only melts again when its temperature reaches 185ºF/85ºC. So an agar gel won’t melt in the mouth; it must be chewed into particles. On the other hand, it will remain solid on hot days, and can even be served hot. Modern cooks have used this property to disperse small agar-gelled morsels of contrasting flavor into a hot dish.

Carrageenan, Alginates, Gellan Experimentally minded cooks are exploring a number of other unusual carbohydrate gelling agents, some traditional and some not. Carrageenan, from certain red algae(p. 341), has long been used in China to gel stews and flavored liquids, and in Ireland to make a kind of milk pudding. Purified fractions of crude carrageenan produce gels with a range of textures, from brittle to elastic. Alginates come from a number of brown seaweeds, and form gels only in the presence of calcium (in milk and cream, for example). Inventive cooks have taken advantage of this to make small flavored spheres and threads: they prepare a calcium-free alginate solution of the desired flavor and color, and then drip or inject it into a calcium solution, where it immediately gels. Gellan, an industrial discovery, is a carbohydrate secreted by a bacterium, and in the presence of salts or acid forms very clear gels that release their flavor well.

Sauces Thickened
with Flour and Starch

Many sauces, from long-simmered classic French brown sauces to last-minute gravies, owe at least part of their consistency to the substance called starch. Unlike the other thickening agents, starch is a major component of our daily diet. It’s the molecule in which most plants store the energy they generate from photosynthesis, and provides about three-quarters of the calories for the earth’s human population, mainly in the form of grains and root vegetables. It’s the least expensive and most versatile thickener the cook has to work with, a worthy adjunct to gelatin and fat. The cook can choose among several different kinds of starch, each with its own qualities.

The Nature of Starch

Starch molecules are long chains of thousands of glucose sugar molecules linked up together. There are two kinds of starch molecules: long straight chains called amylose, and short, branched, bushy chains called amylopectin. Plants deposit starch molecules in microscopic solid granules. The size, shape, amylose and amylopectin contents, and cooking qualities of the starch granules vary from species to species.

Linear Amylose and Bushy Amylopectin The shapes of amylose and amylopectin molecules have a direct effect on their ability to thicken a sauce. The straight amylose chains coil up into long helical structures when dissolved in water, but they retain their basically linear shape. Their elongation makes it very likely that one chain will knock into another or into a granule: each sweeps through a relatively large volume of liquid. By contrast, the branched shape of amylopectin makes for a compact target and therefore a molecule less likely to collide with others; and even if it does collide, it’s less likely to get tangled up and slow the motion of other molecules and granules in the vicinity. A small number of very long amylose molecules, then, will do the job of more but shorter amylose molecules, and of many more bushy amylopectins. For this reason, the cook can obtain the same degree of thickening from a smaller amount of long-amylose potato starch than from moderate-amylose wheat and corn starches.

Two kinds of starch. Starch molecules are chains made up of hundreds or thousands of glucose molecules bonded together. They take two forms: straight chains of amylose (left), and branched chains of amylopectin (right). A long amylose chain moves around in a larger volume than the more compact amylopectin containing the same number of glucose molecules, and is more likely to tangle with other chains. Amylose is therefore a more effective thickener than amylopectin.

Swelling and Gelation What makes starch so useful is its behavior in hot water. Mix some flour or cornstarch into cold water, and nothing much happens. The starch granules slowly absorb a limited amount of water, about 30% of their own weight, and they simply sink to the bottom of the pot and sit there. But when the water gets hot enough, the energy of its molecules is sufficient to disrupt the weaker regions of the granule. The granules then absorb more water and swell up, thereby putting greater and greater stress on the more organized, stronger granule regions. Within a certain range of temperatures characteristic of each starch source but usually beginning around 120–140ºF/50–60ºC, the granules suddenly lose their organized structure, absorb a great deal of water, and become amorphous networks of starch and water intermingled. This temperature is called the gelation range, because the granules become individual gels, or water-containing meshworks of long molecules. This range can be recognized by the fact that the initially cloudy suspension of granules suddenly becomes more translucent. The individual starch molecules become less closely packed together and don’t deflect as many light rays, and so the mixture becomes clearer.

Thickening: The Granules Leak Starch Depending on how concentrated the starch granules are to begin with, the starch-water mixture may noticeably thicken at various points during their swelling and gelation. Most sauces are rather dilute (less than 5% starch by weight) and thicken during gelation, when the mixture begins to become translucent. They reach their greatest thickness after the gelated granules begin to leak amylose and amylopectin molecules into the surrounding liquid. The long amylose molecules form something like a three-dimensional fishnet that not only entraps pockets of water, but blocks the movements of the whale-like, water-swollen starch granules.

Thinning: The Granules Break Once it reaches its thickest consistency, the starch-water mixture will slowly thin out again. There are three different things that the cook may do that encourage thinning: heating for a long period of time after thickening occurs, heating all the way to the boil, and vigorous stirring. All of these have the same effect: they shatter the swollen and fragile granules into very small fragments. While this does mean that even more amylose is released into the water, it also means that there are many fewer large bodies to get caught in the amylose tangle. In other words, the amount of netting increases, the mesh grows finer, but at the same time the big whales become small minnows. This thinning effect is especially striking in the case of very thick pastes, less obvious in normal sauces. If the granules are few and far between to begin with, their disintegration is less noticeable. This thinning is accompanied by a greater refinement of texture, as the starch particles disappear and only indetectably small molecules remain.

Some of the thinning of long-simmered starch-based sauces is caused by the gradual breakdown of the starch molecules themselves into smaller fragments. Acidity accelerates this breakdown.

Thickening a sauce with starch. Uncooked starch granules offer little obstruction to the flow of the surrounding liquid (left). As the sauce heats up and the temperature reaches the gelation range, the granules absorb water and swell, and the sauce consistency begins to thicken (center). As cooking continues and the temperature approaches the boil, the granules swell even more and leak starch chains into the liquid (right). It’s at this stage that the sauce reaches its maximum thickness.

Cooling, Further Thickening, and Congealing Once the starch in a sauce has gelated, its amylose has leaked out, and the cook judges the sauce to be properly cooked, he stops the cooking, and the temperature of the sauce begins to fall. As the mixture cools down, the water and starch molecules move with less and less energy, and at a certain point the force of the temporary bonds among them begins to hold the molecules together longer than they are kept apart by random collisions. Gradually, the longer amylose molecules form stable bonds among themselves, the kind of bonds that held them together in the granule initially. Water molecules settle in the pockets between starch chains. As a result, the liquid mixture gets progressively thicker. If the amylose molecules are concentrated enough, and the temperature falls far enough, the liquid mixture congeals into a solid gel, just as a gelatin solution settles into a jelly. (Bushy amylopectin molecules take much longer to bond to each other, so low-amylose starches are slow to congeal.) This is the way in which pie fillings, puddings, and similar solid but moist starch concoctions are made.

Judge Sauce Consistency at Serving Temperatures It’s important for the cook to anticipate this cooling and thickening. We create and evaluate most sauces on the stove at high temperatures, around 200ºF/93ºC, but when they’re poured in a thin layer onto food and served, they immediately begin to cool and thicken. However thick a sauce is in the pan, it’s going to be thicker when the diner actually tastes it, and it may even congeal on the plate. So sauces should be thinner at the stove than they’re meant to be at the table. (Minimizing the amount of thickener will also reduce the extent to which the sauce’s flavor is muted.) The best way to predict the final texture of a sauce is to pour a spoonful into a cool dish and then sample it.

Starch in sauce making. A swollen granule of potato starch caught in a meshwork of molecules freed from it and other granules (left). A starch-thickened sauce is thickest at this stage, when both starch granules and molecules block the movement of water. A granule of wheat starch that has lost nearly all of its starch molecules to the surrounding liquid (right). As the granules in a starch-thickened sauce disintegrate, they no longer get caught in the mesh of free starch, and the sauce thins out.

Different Starches
and Their Qualities

Cooks have several different forms of starch to choose among for thickening sauces, each with its own particular qualities. They fall into two families: starches from grains, including flour and cornstarch, and starches from tubers and roots, including potato starch and arrowroot. Less commonly seen except on the ingredient labels of processed foods is sago starch, from the stem pith of a Pacific palm (Metroxylon sagu).

Grain Starches Starches from grains tend to share several characteristics. Their starch granules are medium-sized, and contain small but significant amounts of lipids (fats, fatty acids, phospholipids) and protein. These impurities somehow give the starch granules some structural stability, which means that it takes a higher temperature to gelate them; and they lend a cloudiness and distinct “cereal” flavor to starch-water mixtures. Light that passes right through a gelated mesh of pure starch and water is scattered by tiny starch-lipid or starch-protein complexes, producing a milky, impenetrable appearance. Grain starches contain a high proportion of moderately long amylose molecules that readily form a network with each other, and so make sauces that quickly thicken and congeal when cooled.

Wheat Flour Wheat flour is made by grinding wheat grains and sieving the bran and germ from the starch-rich endosperm(p. 528). Wheat flour is only about 75% starch, and includes about 10% by weight of protein, mainly the insoluble gluten proteins. It’s therefore a less efficient thickener than pure cornstarch or potato starch; it takes more flour to obtain the same consistency. A common rule of thumb is to use 1.5 times as much flour as starch. Flour has a distinct wheat flavor that cooks often transform by precooking the flour before adding it to a sauce (p. 617). The suspended particles of gluten protein make flour-based sauces especially opaque and give their surface a matte appearance, unless the sauce is cooked for hours and skimmed to remove the gluten.

Cornstarch Cornstarch is practically pure starch and so a more efficient thickener than flour. Cornstarch is manufactured by soaking the whole maize grain, milling it coarsely to remove the germ and hull, and grinding, sieving, and centrifuging the remainder to separate the seed proteins. The resulting starch is washed, dried, and reground into a fine powder consisting of single granules or small aggregates. During this wet processing, the starch granules absorb odors and develop their own when their traces of lipids are oxidized, so cornstarch has a distinctive flavor unlike that of wheat flour, which is milled dry.

Rice Starch Rice starch is seldom seen in Western markets. Its granules have the smallest average size of the starches, and produce an especially fine texture in the early stages of thickening.

Tuber and Root Starches Compared to the starches from dry grains, the starches from moist underground storage organs come in the form of larger granules that retain more water molecules, cook faster, and release starch at lower temperatures. They contain less amylose, but their amylose chains are up to four times longer than cereal amyloses. Root and tuber starches contain a fraction of the lipids and proteins that are associated with cereal starches, which makes them more readily gelated — lipids delay gelation by stabilizing granule structure — and gives them less pronounced flavors. These starches leave their sauces with a translucent, glossy appearance. The properties of root starches suit them for last-minute corrections of sauce consistency: less of them is required to lend a given thickness, they thicken quickly, and don’t need precooking to improve their flavor.

Potato Starch Potato starch was the first commercially important refined starch and is still an important food starch in Europe. It is unusual for several characteristics. Its granules are very large, up to a tenth of a millimeter across, and its amylose molecules are very long. This combination gives potato starch an initial thickening power far greater than that of any other starch. The long amylose chains tangle with each other and with the giant granules to block easy movement of the sauce fluid. This entanglement also creates long aggregates of amylose and granules that can give the impression of stringiness. And the large swollen granules give a noticeable initial graininess to sauces. However the granules are fragile, and readily fragment into finer particles; so having reached its thickest and grainiest, the consistency of a potato-starch sauce rapidly gets both finer and thinner. Potato starch is also unusual for having a large number of attached phosphate groups, which carry a weak electric charge and cause the starch chains to repel each other. This repulsion helps keep the starch chains evenly dispersed in a sauce, and contributes to the thickness and clarity of the dispersion and its low tendency to congeal into a gel on cooling.

Tapioca Tapioca, derived from the root of a tropical plant known as manioc or cassava (Manihot esculenta, p. 305), is a root starch used mostly in puddings. It tends to form unpleasantly stringy associations in water and so is usually made into large pregelatinized pearls (p. 578), which are then cooked only long enough to be softened. Because tapioca keeps well in the ground and is processed into starch within days of harvest, it doesn’t develop the strong aromas found in wheat and corn starches or in potato starch, which is typically extracted from long-stored, second-quality tubers. Tapioca starch is especially prized for its neutral flavor.

Arrowroot Arrowroot starch as it’s known in the West is refined from the roots of a West Indian plant (Maranta arundinacea). Arrowroot starch has smaller granules than potato or tapioca starches, produces a less stringy consistency, and doesn’t thin out as much on prolonged cooking. Its gelation temperature is higher than the other root starches, more like the range for cornstarch. A number of other plants and their starches are also called arrowroot in Asia and Australia (species of Tacca, Hutchenia, Canna).

Root Starches in China In China, starch was originally extracted from millet and water chestnuts. Nowadays most Chinese sauces are thickened with corn, potato, or sweet potato starch — all plants from the New World. Other Asian sources of starch are yams, ginger, lotus, and the tuber of the kudzu vine (Pueraria).

Modified Starches Food manufacturers have not been content with the starches available in nature, mainly because the consistency they create isn’t stable throughout the cycle of production, distribution, storage, and use by the consumer. They’ve therefore engineered a variety of starches that are more stable. Plant breeders have developed so-called “waxy” varieties of corn whose seeds contain little or no amylose and are nearly all amylopectin, which doesn’t form networks as readily as amylose. Waxy starches therefore make sauces and gels that resist congealing and separation into a firm solid phase and watery residue, a problem to which high-amylose starches are prone.

Ingredient manufacturers also use physical and chemical treatments to modify the starch molecules from standard plant varieties. They precook and dry starches in various ways to produce powders or granules that readily absorb cold water or disperse in and thicken liquids without requiring cooking. And they alter them with chemicals — cross-linking chains to each other, or oxidizing them, or substituting fat-soluble side groups along the chain — to make them less prone to breakdown during cooking, to make them more effective emulsion stabilizers, and to give them other qualities that “native” starches don’t normally have. Such starches are listed on ingredient labels as “modified starch.”

The Influence of Other
Ingredients on Starch Sauces

Flavorings: Salt, Sugar, Acid Starch and water are the basis for a sauce’s structure, and most other ingredients have only secondary effects on that structure. Salt, acid, and sugar are frequently added for their contributions to flavor. Salt slightly lowers the gelation temperature of starch, while sugars increase it. Acids in the form of wine or vinegar encourage the fragmentation of starch chains into much shorter lengths, so that starch granules gelate and disintegrate at lower temperatures, and the final product is less viscous for a given amount of starch. Root starches are noticeably affected by moderate acidity (a pH lower than 5), while grain starches can withstand the acidities typical of yogurt and many fruits (pH 4). Gentle and brief cooking will minimize acid breakdown.

Proteins and Fats Two other materials are commonly found in sauces and have some influence on their texture. Flour is about 10% protein by weight, and much of this fraction is insoluble gluten. Gluten aggregations probably get caught in the starch network and so slightly increase the viscosity of the solution, though the pure starches are generally more powerful thickeners overall. Sauces based on concentrated meat stocks also contain a good deal of gelatin, but gelatin and starch seem not to affect each other’s behavior.

Finally, fats are usually present in the form of butter, oil, or the drippings from a roast. They do not mix with water or water-soluble compounds, but they do slow the penetration of water into starch granules. Fat does contribute the sensations of smoothness and moistness to a sauce, and when used to precook the flour in a roux, it coats the flour particles, prevents them from clumping together in the water, and so safeguards against lumps.

Incorporating Starch into
Sauces

In order to thicken a sauce with starch, the cook must get the starch into the sauce. Very basic, but not so simple! If you add flour or starch directly to a hot sauce, it lumps up and never disperses evenly: the moment they hit the hot liquid, the clumps of starch granules develop a partly gelated, sticky surface that seals the dry granules inside and prevents them from dispersing.

Slurries, Beurre Manié, Floured Meat Cooks use four methods for incorporating starch into a sauce. The first is to mix the starch with some cold water, so that the granules are wetted and separated before they encounter gelation temperatures. The starch-water slurry can then be added directly to the sauce. A second method is to separate the starch or flour particles not with water, but with fat. Beurre manié, or “kneaded butter,” is flour worked into a paste with its weight in butter. When a piece of the paste is added to a hot sauce in need of last-minute thickening, the butter melts and gradually releases greased starch particles into the liquid, where their swelling and gelation are slowed by the water-repelling surface layer.

A third method for getting starch into a sauce is to introduce it early in the cooking, not late. Many stews and fricassees are made by dusting pieces of meat with flour, then sautéing the pieces, and only then adding a cooking liquid that will become the sauce. In this way the starch has already been dispersed over the large surface area of the meat pieces, and it has been precoated with the sautéing fat, which prevents clumping when the liquid is added.

Roux The fourth method for getting starch into a sauce, and one that has been developed into a minor art of its own, is to preheat the starch separately in fat to make what the French call a roux, from the word for “red.” The basic principle works with any form of starch and any fat or oil. In the traditional French system, the cook carefully heats equal weights of flour and butter in a pan to one of three consecutive endpoints: the mixture has had the moisture cooked out of it, but the flour remains white; the flour develops a light yellow color; or the flour develops a distinctly brown color.

Improvements in Flavor, Color, and Dispersability In addition to coating the flour particles with fat and making them easier to disperse in a hot liquid, roux making has three other useful effects on the flour. First, it cooks out the raw cereal flavor and develops a rounded, toasty flavor that becomes more pronounced and intense as the color darkens. Second, the color itself — the product of the same browning reactions between carbohydrates and proteins that produce the toasty flavor — can lend some depth to the color of the sauce.

Finally, the heat causes some of the starch chains to split, and then to form new bonds with each other. This generally means that long chains and branches are broken down into smaller pieces that then form short branches on other molecules. The short, branched molecules are less efficient at thickening liquids than the long chains, but they’re also slower to bond to each other and form a continuous network as the liquid cools. The sauce is therefore less prone to congeal on the plate. The darker the roux, the more starch chains are modified in this way, and so the more roux is required to create a given thickness. It takes more of a dark brown roux than a light one to thicken a given amount of liquid. (The industrial version of roux making to make a starch more dispersable and stable to cooling is called dextrinization, and involves heating dry starch together with some dilute acid or alkali to 375ºF/190ºC.)

Outside of France, roux are especially prominent in the cooking of New Orleans, where flour is cooked to a number of different stages from pale to chocolate-brown, and where cooks may use several roux in a single gumbo or stew to lend their distinct layers of flavor.

Starch in Classic French Sauces

In the code formalized by Auguste Escoffier in 1902, there are three leading mother sauces that are thickened in part with flour: the stock-based brown and white sauces, or espagnole and velouté; and the milk-based béchamel. Each of these relies on a distinctive combination of roux and liquid. Brown sauce consists of a stock made from browned vegetables, meat, and bones, then reduced after thickening with a roux that is cooked until the flour browns as well. White sauce uses a stock made from un browned meat, vegetables, and bones, and is bound with a pale yellow roux. Béchamel combines milk with a roux that is not allowed to change color at all. From these three parent sauces, the cook can produce scores of offspring simply by finishing the sauce with different seasonings and enrichments.

Once the roux has been added to the stock, the mixture is allowed to simmer for quite a while — two hours for velouté, and up to ten in the case of brown sauce. During this time, the flavor is concentrated as water evaporates, and the starch granules dissolve and disperse among the gelatin molecules, with a very smooth texture the result. Brown sauce is cooked for the longest time because it’s meant to be quite clear to the eye, and this requires that the gluten proteins coagulate and be carried to the surface, where they and the tomato solids can be skimmed off.

Escoffier said that a sauce should have three characteristics: a “decided” taste, a texture that’s smooth and light without being runny, and a glossy appearance. The taste is a matter of making fine stocks and being judicious in seasoning, while the consistency and appearance depend on how the thickening is accomplished. Generally, long and patient simmering is necessary, so that there will be little or no vestige of granular structure left to the starch, and the insoluble gluten proteins will be caught up in the surface scum and so removed from the sauce. Gelatin contributes some body to the stock-based sauces, but the starch is what gives them most of their viscosity. After reduction, the concentration of starch in these sauces is around 5%, the gelatin concentration probably about half that.

Milk-Based Sauces: Béchamel and Boiled Sauces based on milk rather than stock are of course much easier to make, and more forgiving; because they’re already milky, the cook doesn’t have to worry about long simmering to clarify them. The classic starch-thickened milk sauce is béchamel, whose only other ingredients are seasonings and the butter in which the starch is precooked for a couple of minutes. Once the milk has been added to the roux, the sauce is simmered for 30–60 minutes with occasional skimming of the skin of milk and flour proteins that forms at the surface. Starch is more effective at thickening milk than it is meat stocks, apparently because it bonds both to the milk proteins and the fat globules and so recruits these weighty ingredients into its flow-slowing network. Thanks to its pleasant but neutral flavor, béchamel is a versatile sauce that can be imbued with many flavors and served with many mainingredients. It’s also made in several thicknesses for a variety of purposes. Thick preparations (6% flour by weight) serve as the base for soufflés, somewhat thinner ones as a moistening and enrichment for gratins.

In the “boiled dressing” often used in the United States to moisten coleslaw and other robust salads, flour not only thickens the milk and/or cream, but also helps prevent the vinegar from curdling the milk and egg-yolk proteins into coarse particles.

Gravy

We come now to the homely Anglo-American cousin of French sauces, the starch-thickened gravy typically made to accompany a roast. This is a last-minute sauce that’s put together just before serving, and consists of the roast’s juices, extended with additional liquid, and thickened with flour. The drippings from the roast, both fat and browned solids, give the gravy its flavor and color. First the fat is poured off and reserved, and the pan is “deglazed”: the browned solids are lifted from the roasting pan with a small amount of water, wine, beer, or stock. The liquid dissolves the browning-reaction products that have stuck to the pan and so takes up their especially rich flavors. The deglazing liquid is poured off and reserved separately. Now some of the fat is returned to the pan with an equal volume of flour, and the flour cooked until it has lost its raw aroma. The deglazing liquid is added, around a cup/250 ml for every 1–2 tablespoons/10–20 gm flour. The mixture is cooked until it thickens, a matter of a few minutes.

Because they’re made at the last minute, gravies are not cooked long enough to cause the disintegration of the starch granules, and therefore generally have a slightly coarse texture, even when lump-free. This gives gravies a character very different from that of the suave sauce: hearty, and when they are extremely thick, almost bready. The cook can obtain a smoother consistency by making an initial preparation from the flour and a fraction of the deglazing liquid, heating the mixture until the starch granules gelate and crowd up against each other to form a thick paste, and whisking the paste vigorously to smash the granules into each other and break them up into finer pieces. This paste is then mixed with the rest of the deglazing liquid and simmered until it’s evenly dispersed and the liquid reaches the desired consistency.

Sauces Thickened with
Plant Particles: Purees

Some of the most delicious sauces we eat, including tomato sauces and applesauce, are made simply by crushing fruits and vegetables. Crushing, or pureeing, frees the juices from the cells of the fruit or vegetable, and breaks the cell walls into fragments that become suspended in the juices and block their flow, so giving them some thickness. Crushed nuts and spices have no juices of their own, but they thicken a liquid to which they’re added by absorbing some of its water and providing dry cell particles that obstruct the liquid’s flow.

Until recently, most purees of plant tissue would have been made by cooking the tissue to soften it, and then either grinding it in a mortar or forcing it through a fine sieve. Raw purees could only be made from fruits softened by ripening, or from brittle nuts. Today’s cooks can use powerful machines — blenders, food processors — to puree any fruit or vegetable or seed with ease, whether they’re raw or cooked.

Plant Particles: Coarse
and Inefficient Thickeners

Compared to the other ways of thickening, simple pureeing tends to produce a coarse sauce that more readily separates into solid particles and thin fluid. The solid fragments of plant cell walls are clumps of many thousands of carbohydrate and protein molecules. If those molecules were dispersed separately and finely throughout the fluid — as gelatin or starch molecules are in other sauces — they would bind many more water molecules, get tangled up in each other, and be far too small for the tongue to detect as particles. But plant-cell fragments range from 0.01 to 1 millimeter across; they give a grainy impression on the tongue and they’re far less efficient than individual molecules at binding water or interfering with fluid flow. And because the fragments are usually denser than the cell fluids, they end up sinking and separating from the fluids. Heating without stirring tends to speed this separation, because the free water is able to flow and rise from the bottom of the pot through the thicker particle phase, and accumulate above it.

Some sauces and related preparations aren’t meant to be suave and smooth; instead the cook leaves some pieces of tissue intact to highlight the texture of the fruit or vegetable itself. Mexican tomato and tomatillo salsas, unstrained cranberry sauce, and applesauce are familiar examples.

Refining the Texture of Purees Cooks can refine the basic coarseness of purees by modifying either the solid plant particles or the fluid that surrounds them.

Making the Plant Particles Smaller There are several ways to make the plant particles as fine as possible.

• The pureeing process itself is a physical crushing or shearing that breaks the plant tissue into pieces and liberates thickening molecules from them. Blenders and mortars are the most effective tools for this; food processors slice rather than crush. Producing a fine puree can take some time even in a blender, several minutes or more.
• Straining through a sieve or cheesecloth removes the large particles, and forcing the puree through a fine mesh breaks large particles into smaller ones.
• Heating softens cell walls so that they’ll break into smaller pieces, and shakes loose long-chain carbohydrates from the cell walls and gets them into the watery phase, where they can act as separate starch and gelatin molecules do.
• Freezing a puree and then thawing it causes ice crystals to damage cell walls, which can help liberate more pectin and hemicellulose molecules into the liquid.

A fruit or vegetable puree. Grinding plant tissue turns it inside out, freeing the cell fluids and breaking the cell walls and other structures into small particles. A puree is a mixture of plant particles and molecules floating in water (left). If left to stand, most purees will separate, with the larger particles settling to the bottom (center). This separation can be prevented, and the puree consistency thickened, by cooking the puree down and evaporating the excess water (right).

Preventing Separation The consistency of a puree is also improved by reducing the amount of water in the continuous phase. The simplest way to do this is to cook the whole puree down, simmering gently, until the separate thin phase disappears. Another way that better preserves the puree’s fresh flavor is to drain the thin fluid off the solids and either discard it, or cook it down separately and then add it back. Or the cook can remove some of the fruit’s or vegetable’s water before crushing it, for example by partly drying halved tomatoes in the oven.

The binding power of the puree particles themselves can be supplemented by adding some other thickener, dry spices or nuts for example, or flour or starch.

Fruit and Vegetable Purees

Any fruit or vegetable can be turned into a sauce by crushing it. Here are brief observations about some of the more commonly pureed foods.

Raw Purees: Fruits Raw purees are generally made from fruits, whose ripening enzymes often break down their cell walls from within, and thus allow their intact flesh to turn into a puree in the mouth. Raspberries, strawberries, melons, mangoes, and bananas are examples of such naturally soft fruits. The flavor of a raw puree is usually accentuated by the addition of sugar, lemon juice, and aromatic herbs or spices. But that flavor is fragile and changeable. Pureeing mixes the cell contents with each other and with oxygen in the air, so enzyme action and oxidation begin immediately (see below for the effects in cooked purees of tomato, a botanical fruit). The best way to minimize this change is to chill the puree, which slows all chemical reactions.

Raw Purees: Pesto The Italian puree of basil leaves, pesto genovese, also contains olive oil and so is partly an emulsion as well. Pesto takes its name from the same root that gives us pestle, and the basil leaves and garlic were traditionally ground with a pestle and mortar. Because this takes some time and effort, modern cooks usually prepare pesto in a blender or food processor. The choice of appliance and how it’s used influence both consistency and flavor. The crushing and shearing action of the pestle, the shearing action of the blender, and the slicing action of the processor all produce different proportions of intact and broken cells. The more thoroughly the cells are broken, the more their contents are exposed to each other and to the air, and the more their flavor evolves. A coarse pesto will have a flavor most like the flavor of fresh basil leaves.

Cooked Purees: Vegetables, Applesauce Most vegetable purees are made by first cooking the vegetable to soften its tissues, break apart the cells, and free their thickening molecules. Some that develop an especially suave smoothness have cell walls rich in soluble pectin, which escapes from the softened wall fragments during pureeing. These vegetables include carrots, cauliflower, and capsicum peppers; more than 75% of the cell-wall solids in capsicum puree is pectin. Many root and tuber vegetables (though not carrots) contain starch granules, which when cooked absorb much of the water in the vegetable and make it less watery. However, such vegetables are best crushed gently, without breaking open the cells. Thorough pureeing that liberates the gelated starch turns the vegetable into a super-thick potato gravy, gluey and stringy.

Even though fruits are presoftened by ripening, cooks often heat them to improve their texture, flavor, and storage life. One of the most popular cooked fruit sauces is applesauce, which is meant to have a certain coarseness and yet not seem grainy. The cells of different varieties have different tendencies to adhere to each other, and that tendency can change with time in storage. Most of the soft varieties used to make sauce produce finer-grained purees with time, while the Macintosh produces coarser ones.

Tomato Sauce: The Importance of Enzymes and Temperatures The most familiar vegetable puree in the West, and perhaps in the world, is tomato sauce and paste. The solids in tomatoes are about two-thirds flavorful sugars and organic acids, and 20% cell-wall carbohydrates that have some thickening power (10% cellulose, and 5% each pectin and hemicelluloses). In the United States, commercial tomato purees may include all the water in the original tomatoes, or just a third. Tomato paste is tomato puree cooked down so that it contains less than a fifth of the water of the raw vegetable. Tomato paste is thus a concentrated source of flavor, color, and thickening power. (It’s also an effective emulsion stabilizer; see p. 628.)

There are several variables in the preparation of purees that can affect their final texture and flavor. Food scientists have shown this most clearly for mass-produced tomato puree. The general lessons are also relevant to the preparation of purees from other fruits and vegetables.

Tomato Enzymes and Consistency The final consistency of a tomato puree depends not just on how much water has been removed, but also on how long the puree spends at either moderate or high temperatures. Ripe tomatoes have very active enzymes whose job is to break down pectin and cellulose molecules in the fruit cell walls, and so give the fruit its soft, fragile texture. When the tomatoes are firstcrushed, the enzymes and their target molecules are thoroughly mixed together, and the enzymes start breaking down the cell-wall structures. If the raw puree is held at room temperature for a while, or heated to a temperature below the denaturation temperature of the pectin enzymes, around 180ºF/80ºC, then the enzymes will break down a lot of the cell-wall reinforcements, and these liberated molecules will give a noticeably thicker consistency to the puree.

However, when the puree is then heated to remove water and concentrate it, the high temperatures break the already enzyme-damaged molecules into smaller pieces that are less efficient thickeners, and the paste requires that much greater reduction to obtain the desired thickness. If instead the raw puree is cooked quickly close to the boil, the result is a thicker sauce that requires less subsequent reduction. The pectin and cellulose enzymes are denatured and become inactive, while at the same time the cell walls are disrupted by the heat. The cell-wall pectins that escape into the fluid phase during the concentration heating are longer molecules and more efficient thickeners.

Tomato Enzymes and Flavor In addition to tomato enzymes that affect texture, there are enzymes that affect flavor: and in the case of flavor, some initial enzyme activity can be desirable. The fresh, “green”-smelling molecules (hexanal and hexanol, p. 274) that are an important element in ripe tomato flavor are generated by the action of enzymes on fatty acids when the fruit tissue is crushed, either in the mouth or in the pot. Rapid cooking to the boil minimizes this fresh flavor element, while allowing the raw puree to sit at room temperature — in a Mexican salsa, for example — or only slowly heating it, will cause the accumulation of these flavor molecules in the puree. A method that home cooks sometimes use is to halve or quarter tomatoes, then bake them in a slow oven to remove water, and finally cook them relatively quickly into a sauce. This technique minimizes the mixing of enzymes and targets, so cells stay relatively intact, and relatively little green aroma develops.

Then there’s the traditional Italian preparation called estratto, which begins with fresh tomatoes cooked down to some extent, and then mixes them with some olive oil and spreads the paste on boards to dry down further in the sun. This is often described as a relatively “gentle” process compared to cooking, and it probably does spare some damage to the pectin molecules. But in fact it subjects a number of sensitive molecules — including the antioxidant tomato pigment lycopene and unsaturated fatty acids in the olive oil — to powerful and damaging ultraviolet light, which gives estratto a distinctively strong, cooked flavor.

Nuts and Spices as Thickeners

Among seeds and other dry plant materials, only oily nuts can be made into a sauce base on their own. When such nuts are ground into “butters,” the oil provides the fluid continuous phase that lubricates the particles of cell walls and proteins. But most of the time, nuts are mixed with other ingredients, including liquids, so they become part of a complex suspension and help thicken both with their dry particles and with their oil, which becomes emulsified into tiny droplets. Almonds have long served this purpose in the Middle East and Mediterranean in such sauces as romesco (with red peppers, tomatoes, and olive oil) and picada (garlic, parsley, oil), and the coconut in tropical Asia, where it’s pounded along with spices and herbs to become part of the sauce for cooked meats, fish, and vegetables.

Nuts and other finely ground seeds and spices help thicken liquid sauces thanks to their very dryness, which allows their particles to absorb water from the sauce and thus reduce the amount of liquid that needs to be filled with particles. At the same time, the particles themselves swell and become larger obstacles to the liquid’s flow. Dry spices such as turmeric, cumin, and cinnamon are both flavorings and thickeners in Indian sauces, and coriander is especially effective thanks to its fibrous, absorbant seed coat. Dried chilli peppers, ground nuts, and spices thicken Mexican mole sauces. Powdered versions of dried chilli pepper are prominent in Spanish and Hungarian sauces (pimenton, paprika); mustard is also widely used. Some spices also release efficient thickening molecules into the liquid. Fenugreek seeds exude a gum that gives a gelatinous consistency to the Yemeni sauce hilbeh; and the dried leaves of the sassafras tree, ground to make filé powder, release carbohydrates that give Louisiana gumbos a slightly stringy viscosity.

Complex Mixtures:
Indian Curries, Mexican Moles

The most complex and sophisticated puree sauces are made in Asia and Mexico. The sauce or “gravy” for many Indian and Thai dishes begins with finely ground plant tissues — onions, ginger, garlic in northern India, coconut in southern India and in Thailand — and a number of different spices and herbs. These ingredients are then fried in hot oil until much of the moisture has boiled off, and the plant solids are sufficiently concentrated that the sauce clings to itself and the oil separates. The frying also cooks the sauce, eliminating raw flavors and developing new ones. The sauce is then slightly thinned with some water, and the main ingredient cooked in it. Mexican mole sauces are prepared in much the same way, except that the foundation ingredient is usually rehydrated dried chillis; pumpkin and other seeds are another major element. Thanks to the high pectin content of the chillis, moles have a more suave, finer consistency than the Asian purees. But both are marvels of mouth-filling pleasure.

Sauces Thickened
with Droplets of Oil
or Water: Emulsions

The sauces we’ve examined so far are liquids thickened with a fine dispersion of solid materials: protein molecules, starch granules and molecules, particles of plant tissue and cell-wall molecules. A very different thickening method is to fill the water-based liquid with droplets of oil, which are much more massive and slow-moving than individual molecules of water, impede their motion, and so create a thick and creamy consistency in the mixture as a whole. Such a dispersion of one liquid in another is called an emulsion. The word comes from the Latin for “to milk out,” and referred originally to the milky fluids that can be pressed from nuts and other plant tissues. Milk, cream, and egg yolks are natural emulsions, while sauce emulsions include mayonnaise, hollandaise sauce, beurre blanc, and oil-and-vinegar salad dressings. Modern chefs have applied the basic idea to the thickening of all kinds of liquids, and often actually describe the result on the menu as an emulsion, a word that lingers on the tongue longer than sauce does.

Emulsified sauces offer a special challenge to the cook: unlike sauces thickened with solids, emulsions are basically unstable. Whisk oil and a little vinegar together in a bowl, and the vinegar forms droplets in the oil: but they soon sink and coalesce, and in a few minutes the two liquids have separated again. Cooks not only have to form the emulsion, they also have to prevent the emulsion from being undone by the basic incompatibility of the two liquids.

The Nature of Emulsions

An emulsion can only be made from two liquids that don’t dissolve in each other, and therefore retain their distinct identities even when mixed. The molecules of water and alcohol, for example, mix freely and so can’t form an emulsion. In addition to sauces, cosmetic creams, floor and furniture waxes, some paints, asphalt, and crude oil are all emulsions of water and oil.

Two Liquids: Continuous and Divided The two liquids in an emulsion can be thought of as the container and the contained: one liquid is broken up into separate droplets, and these droplets are contained in and surrounded by the intact mass of the other liquid. In the usual shorthand, an “oil-in-water” emulsion is one in which oil is dispersed in a continuous water phase; “water-in-oil” names the reverse situation. The dispersed liquid takes the form of tiny droplets, between a ten-thousandth and a tenth of a millimeter across. The droplets are large enough to deflect light rays from their normal path through the surrounding liquid, and give emulsions their characteristically milky appearance.

The more droplets that are crowded into the continuous phase, the more they get in the water’s and each other’s way, and the more viscous the emulsion is. In light cream, the fat droplets take up about 20% of the total volume and water 80%; in heavy cream, the droplets are about 40% of the volume; and in stiff, semisolid mayonnaise, oil droplets occupy nearly 80% of the volume. If the cook works more of the dispersed liquid into the emulsion, then it gets thicker; if he adds more of the continuous liquid, then there’s more space between droplets, and the emulsion becomes thinner. Clearly it’s important to keep in mind which phase is which.

Because nearly all emulsified sauces are oil-in-water systems, I’ll assume in most of the following discussion that the continuous phase is water, the dispersed phase oil.

Forming Emulsions: Overcoming the Force of Surface Tension It takes work to make an emulsion. We all know from experience that when we pour water and oil into the same bowl, they form two separate layers: one doesn’t just turn into tiny droplets and invade the other. The reason for this behavior is that when liquids can’t mix for chemical reasons, they spontaneously arrange themselves in a way that minimizes their contact with each other. They form a single large mass, which exposes less surface area to the other liquid than does the same total mass broken into pieces. This tendency of liquids to minimize their surface area is an expression of the force called surface tension.

Mayonnaise formation. Two stages in making mayonnaise as seen through a light microscope. One tablespoon/15 ml of oil beaten into 1 egg yolk plus water gives a sparse emulsion of coarse, unevenly sized oil droplets (left). Eight tablespoons/120 ml of oil give a tightly packed, semisolid emulsion of small droplets (right). The yolk emulsifiers and stabilizing proteins must be effective enough to withstand considerable physical pressure in order to prevent the oil droplets from coalescing into a separate layer.

Making Billions of Droplets from One Tablespoon It’s on account of surface tension, then, that the cook must pour energy into the liquid to be dispersed. To make a sauce, its natural monolithic arrangement must be shattered. And seriously shattered: when you beat a single tablespoon/15 ml of oil into a mayonnaise, you break it up into about 30 billion separate droplets! Serious whisking by hand or in a kitchen mixer provides enough shearing force to make droplets as small as 3 thousandths of a millimeter across. A blender can get them somewhat smaller, and a powerful industrial homogenizer can reduce them to less than one thousandth of a millimeter. The size of the droplets matters, because smaller droplets are less likely to coalesce with each other and break the sauce into two separate phases again. They also produce a thicker, finer consistency, and seem more flavorful because they have a larger surface area from which aroma molecules can escape and reach our nose.

Two factors make it easier for the cook to generate small droplets. One is the thickness of the continuous phase, which drags harder on the droplets and transfers more shearing force to them from the whisk. Shake a little oil in a bottle of water, and the oil droplets are coarse and quickly coalesce; shake a little water in the more viscous oil, and the water gets broken into a persistent cloud of small droplets. It’s helpful, then, to start with as viscous a part of the continuous phase as possible, and dilute it with any other ingredients after the emulsion has formed.

The second factor that makes it easier to produce small droplets in an emulsion is the presence of emulsifiers.

Emulsifiers: Lecithin and Proteins Emulsifiers are molecules that lower the surface tension of one liquid dispersed in another, and therefore make it easier to make small droplets and a fine, creamy emulsion. They do so by coating the surface of the droplets, and shielding the droplet surface from the continuous liquid. Emulsifiers are therefore a true liaison: they must be partly soluble in each of the two mutually incompatible liquids. They manage this by having two different regions on the same molecule, one soluble in water and the other in fat.

There are two general kinds of molecules that can act as emulsifiers. One kind is typified by the egg phosopholipid lecithin. These are relatively small molecules with a fat-like tail that buries itself in the fat phase and an electrically-charged head that is attracted to water molecules (p. 802). The other kind of emulsifier is the proteins, which are much larger molecules, long chains of amino acids that have a number of different fat-compatible and water-compatible regions. The yolk proteins in eggs and the casein proteins in milk and cream are the best protein emulsifiers.

Unstable and stable emulsions. Oil and water are incompatible substances; they can’t mix evenly with each other. When oil is whisked into water, the resulting oil droplets tend to coalesce with each other and separate into a layer on top of the water (left). Emulsifiers are molecules with a fat-compatible tail and water-compatible head (p. 802). They embed their long tails in the fat droplets, leaving their electrically-charged heads projecting into the surrounding water. Coated in this way, the droplets repel each other instead of coalescing (center). Large water-soluble molecules, including starch and proteins, help stabilize emulsions by blocking the fat droplets from each other (right).

Stabilizers: Proteins, Starch, Plant Particles Emulsifiers make it easier for the cook to prepare an emulsion, but they don’t necessarily result in a stable emulsion. Once formed, the droplets may be so crowded that they bump into each other or are forced up against each other, and the force of surface tension may pull them together and cause them to coalesce again. Fortunately, there are many kinds of molecules and particles that can help stabilize an emulsion once it’s formed. They all have in common the property of getting in the way, so that two approaching droplets encounter the stabilizers rather than each other. Large, bulky molecules like proteins do this well, as do starch, pectins, and gums, and particles of pulverized plant tissue. Ground white mustard seed is especially effective thanks both to its particles and to a gum that it releases when wetted. Tomato paste contains a considerable amount of protein (around 3%) as well as cell particles, and is a useful emulsifier and stabilizer.

Guidelines for Successful
Emulsified Sauces

Forming Emulsions Emulsions have always been considered fickle concoctions, by chemists as well as cooks. One chemist wrote in 1921 that contemporary books on pharmacy were “filled with elaborate details as to the making of emulsions,” and recorded two such details: “If one starts stirring to the right, one must continue stirring to the right, or no emulsion will be formed. Some books go so far as to say that a left-handed man cannot make an emulsion, but that seems a little absurd.” The worry is always that at some point the emulsion may break and separate into blobs of oil and water again. This can happen, but it’s almost always because the cook has made one of three mistakes: he has added the liquid to be dispersed too quickly to the continuous liquid, or added too much of the dispersed liquid, or allowed the sauce to get either too hot or too cold.

There are several basic rules that apply to the making of any emulsified sauce:

• The first materials into the bowl are the continuous phase — usually the water-based ingredient — and at least some emulsifying and stabilizing ingredients. The dispersed phase is always added to the continuous phase, not the other way around: otherwise it can’t be dispersed!
• The dispersed phase should be added very gradually to begin with, a small spoonful at a time, while the cook whisks or blends the mixture vigorously. Only after an emulsion has formed and developed some viscosity should the oil be added more rapidly.
• The proportions of the two phases must be kept in balance. For most emulsified sauces, the volume of the dispersed phase shouldn’t exceed three times the volume of the continuous phase. If the droplets are crowded so closely together that they are in continuous contact, then they’re more likely to pool together. When the consistency of an emulsion becomes stiff, this is a sign that the cook should add more of the continuous phase to give the droplets more room.

Starting Slowly There’s a simple reason for starting the emulsion slowly and carefully, with small amounts of the dispersed phase. In the early mixing, when little or no oil has yet been emulsified, it’s easy for large droplets to avoid the churning action of the whisk and collect at the surface. If a large volume of oil is added before the previous one has been fully emulsified, then the bowl may end up with more unemulsified oil than water. The oil then becomes the continuous phase, the normally continuous water becomes dispersed in it, and the result is an inside-out emulsion, oily and runny. By whisking in the first portion of oil in small doses, the cook makes sure to produce and maintain a growing population of small droplets. Then when the rest of the oil is incorporated more rapidly into the already well-emulsified system, the existing droplets work as a kind of mill, automatically breaking down the incoming oil into particles of their own size. In the last stages of sauce making the cook’s whisk need not break up the oil drops directly, but has the easier job of mixing the new oil with the sauce, distributing it evenly to all parts of the droplet “mill.”

Using and Storing Emulsified Sauces Once emulsified sauces have been successfully made, there are two basic rules for using them.

• The sauce must not get too hot. At high temperatures, the molecules and droplets in a sauce are moving very energetically, and the droplets may collide hard enough to coalesce. Temperatures above 140ºF/60ºC also cause the proteins in egg-emulsified sauces to coagulate, so they’re no longer able to protect the droplets. And a cooked sauce that is held before serving on gentle heat may lose enough water by evaporation that the dispersed fat droplets become overcrowded. So cooked emulsions should be made and held at warm, rather than hot, temperatures and should not be spooned onto a piece of food still sizzling from the pan.
• The sauce must not get too cold. At low temperatures, surface tension increases, making it more likely that neighboring droplets will coalesce. Butterfat solidifies at room temperature, and some oils do so in the refrigerator. The resulting sharp-edged fat crystals rupture the layer of emulsifier on the droplets, so that they coalesce and separate when stirred or warmed. Refrigerated emulsions often need to be reemulsified before use. (Manufactured mayonnaise is made with oils that remain liquid at refrigerator temperatures.)

Rescuing a Separated Sauce When an emulsified sauce breaks and the droplets of the dispersed phase puddle together, there are two ways to reemulsify it. One is simply to throw the sauce in a blender and use its mechanical power to break the dispersed phase apart again. This generally works for sauces that still have plenty of intact emulsifier and stabilizer molecules in the sauce, but not for cooked egg sauces that have been overheated and their proteins coagulated. The second and more reliable technique is to start with a small amount of the continuous phase, perhaps supplemented with an egg yolk and its wealth of emulsifiers and stabilizers, and carefully beat the broken sauce back into it. If proteins in the initial sauce had coagulated from overheating, the lumps should be strained out before reemulsifying; otherwise the rescue process may leave the protein particles too small to strain out, but large enough to leave a grainy impression in the mouth.

Cream and Butter Sauces

Cream and butter don’t need to be made into sauces — they themselves are sauces! In fact they’re prototypes for sauces in general, with their lingering, mouthfilling consistency and rich but delicate flavor. A ramekin of melted butter in which to dip a morsel of lobster or an artichoke leaf, a pour of cream over fresh berries or pastry — these are wonderful combinations. But cream and butter are versatile ingredients, and cooks have found other ways to exploit them in saucemaking.

Milk and Cream Emulsions Cream owes its versatility to its origins in milk. Milk is a complex dispersion whose continuous phase is water, and whose dispersed phases are milkfat in the form of microscopic droplets, or globules, and protein particles in the form of casein aggregates (p. 19). The droplets are coated with a thin membrane of emulsifiers, both lecithin-like phospholipids and certain proteins; and other noncasein proteins float free in the water. Both the globule membranes and the various proteins are tolerant of heat: so plain milk and cream can be boiled hard without the fat globules coalescing and separating, or the proteins coagulating and curdling.

Whole milk is only about 4% fat, so its fat globules are too few and far between to block the flow of the water phase and give much of an impression of thickness. Cream is a portion of milk in which the fat globules have been concentrated and crowded: light cream is around 18% fat, and heavy or whipping cream around 38%. In addition to its fat supply, cream offers proteins and emulsifying molecules that can help stabilize other, more fragile emulsions (beurre blanc).

Heavy Cream Resists Curdling The casein proteins in milk and cream are stable to boiling temperatures, but they’re sensitive to acidity, and the combination of heat and acid will cause them to curdle. Many sauces include flavorful acid ingredients: sauté pans are often deglazed with wine, for example. This means that most milk and cream products, including light cream and sour cream, can’t actually be cooked to make a sauce; they must be added as a last-minute enrichment. The exceptions are heavy cream and crème fraîche, which contain so little casein that its curdling simply isn’t noticeable (p. 29).

Reduced Cream When heavy cream is added to another liquid to enrich and thicken it — to a meat sauce, or deglazing liquid, or a vegetable puree — then of course its fat globules are diluted and its consistency thins down. In order to make cream a more effective thickener, cooks concentrate it even further by boiling off water from the continuous phase. When the volume of cream is reduced by a third, the globule concentration reaches 55% and the consistency is like that of a light starchthickened sauce; when reduced by half, the globules take up 75% of the volume and the consistency is very thick, almost semisolid. Stirred into a thinner liquid, these reduced creams have enough fat globules to fill it and lend a substantial body. Cream reduction and thickening can also be done at the last minute, for example after a sauté pan has been deglazed; the cook adds cream to the deglazing liquid and boils the mixture until it reaches the desired consistency.

Crème Fraîche in Sauce Making Reduced creams have several disadvantages. They take time and attention to prepare, develop a cooked flavor, and are very rich, sometimes overly so for the balance of a given sauce. A useful alternative to reduced creams is crème fraîche, a version of heavy cream whose consistency has been thickened not by boiling down, but by fermentation (p. 49). The acid produced by lactic bacteria causes the casein proteins in the water phase to cluster together and form a network that immobilizes the water. Some strains of bacteria also secrete long carbohydrate molecules that further thicken the water phase and act as stabilizers. Used in place of reduced cream, crème fraîche requires no preparation, is less rich, and has a fresher flavor. Thanks to its low protein content, it tolerates temperatures that would curdle sour cream.

Butter Like its parent material, cream, butter is an emulsion: but it’s one of the few food emulsions in which the continuous phase is fat, not water. In fact, butter is made by “inverting” the fat-in-water cream emulsion to produce a water-in-fat emulsion (p. 33). The continuous fat phase of butter, together with some intact fat globules that survived churning, takes up about 80% of its volume, and the dispersed water droplets about 15%. When it melts, the heavier water droplets sink to the bottom and form a separate layer. The consistency of melted butter, then, is the consistency of the butterfat itself, which thanks to its long fat molecules is naturally more slow-flowing and viscous than water. So melted butter, whole or clarified (“drawn”) to remove the water phase, makes a simple and delicious sauce. Cooks also heat whole butter until the water boils off and the milk solids turn brown, which gives the fat a nutty aroma. The French beurre noisette and beurre noir, or “hazelnut” and “black” butters, are such browned butters, often made into a temporary emulsion with lemon juice and vinegar respectively.

Compound and Whipped Butters There are other ways to take advantage of butter’s semisolid consistency and background richness. One is to make a “compound butter” by incorporating pounded herbs, spices, shellfish eggs or livers, or other ingredients; another is to whip softened butter with a flavorful liquid into a combined emulsion and foam. Pieces or dollops of these flavored butters can then be melted into a rich, flavorful coating atop a piece of meat or fish, or on some vegetables or pasta, or they can be swirled into an otherwise finished sauce.

Turning Butter Back into Cream: Enriching Sauces with Butter Butter is remarkable for being a convertible emulsion. This offspring of cream can be turned back into cream! Its convertibility is what makes butter so useful as a finishing enrichment for many sauces, including simple pan deglazings, and it’s what makes possible the sauce called beurre blanc, literally “white butter.” There’s only one requirement for converting butter into the equivalent of cream with 80% fat: the process must start in a small amount of water. If you melt butter on its own, the fat phase remains the continuous phase, and the water droplets settle out of it. But if you melt butter in some water, then you’re starting with water as the continuous phase. As the fat molecules are released into the water, they’re surrounded by water — and by the substances contained in the butter’s own water droplets, which merge right into the cooking water. The droplets contain milk proteins and remnants of the emulsifier membranes that coated the fat globules in the original cream. And those protein and phospholipid remnants reassemble themselves onto the fat as it melts into the water, coating and protecting separate fat droplets and forming the fat-in-water emulsion. However, the droplet coatings in this reconstituted cream are sparser and more fragile than the original fat-globule membranes, and will begin to leak fat if heated close to 140ºF/60ºC.

Any water-based sauce can thus be thickened and enriched simply by swirling a pat of butter into it at the end. This is especially handy in the last-minute thickening of pan juices, which don’t have the benefit of containing much gelatin or any starch. Incorporating one volume of butter into three volumes of deglazing liquid — off the heat, to avoid damaging the fragile droplet coatings — will produce a consistency (and fat content) approximating that of light cream.

In purees and starch-thickened sauces, a small amount of butter (or cream) lubricates the solid thickeners and lends a smoother consistency. Because these sauces are rich in emulsion-stabilizing molecules and particles, they can be heated to the boil without causing the reconstituted fat droplets to separate.

Beurre Blanc The French sauce beurre blanc probably evolved from the practice of enriching cooking liquids with butter. It’s made by preparing a flavorful reduction of vinegar and/or wine, then whisking pieces of butter into the reduction. Each piece of butter carries all the ingredients necessary for a new portion of sauce, so the cook can whisk in one piece of butter, or 100. The proportions are entirely up to the cook’s taste and needs. The consistency of beurre blanc is like that of thick cream, and can be made somewhat thicker by adding water-free clarified butter once the initial emulsion has been formed. The phospholipids and proteins carried in the butter’s water are capable of emulsifying two to three times the butterfat in which they’re embedded.

Beurre blanc will begin to separate and leak butterfat if its temperature rises above about 135ºF/58ºC. However, the phospholipid emulsifiers can tolerate heat and re-form a protective layer. An overheated sauce can usually be restored with a small amount of cool water and brisk whisking. The addition of a spoonful of cream supplies more emulsifying materials and can make a beurre blanc more stable. Most damaging to beurre blanc is letting it cool below body temperature. The butterfat solidifies and forms crystals around 85ºF/30ºC, and the crystals poke through the thin membrane of emulsifiers and fuse with each other, forming a continuous network of fat that separates when the sauce is reheated. Ideally, beurre blanc should be kept at around 125ºF/52ºC. Because water will evaporate at this temperature and may overconcentrate the fat phase, it’s a good idea to add a little water periodically if the sauce has to be held for any time.

Beurre Monté A preparation closely related to beurre blanc is beurre monté, “worked up” or “prepared” butter, which is simply an unflavored beurre blanc made with an initial dose of water rather than vinegar or wine. Beurre monté is used among other things as a poaching medium. Thanks to the relatively low heat conductivity and heat capacity of fat compared to water, it cooks delicate fish and meats more gradually than does a broth at the same temperature.

Eggs as Emulsifiers

As we’ve already seen, cooks can use egg yolks to thicken all kinds of hot sauces. The yolk proteins unfold and bond to each other when heated, and so form a liquid-immobilizing network (p. 604). Egg yolks are also very effective emulsifiers, and for asimple reason: they themselves are a concentrated and complex emulsion of fat in water, and are therefore filled with emulsifying molecules and molecule aggregates.

Emulsifying Particles and Proteins Of the various yolk components, two in particular provide most of the emulsifying power. One is the low-density lipoproteins or LDLs (the same LDLs that circulate in our blood and whose levels are measured in blood tests because they carry potentially artery-blocking cholesterol). LDLs are particles made up of emulsifying proteins, phospholipids, and cholesterol, all surrounding a core of fat molecules. The intact LDL particles appear to be more effective emulsifiers than any of their components. The other major emulsifying particles are the larger yolk granules, which contain both LDLs and HDLs (the “good-cholesterol” high-density lipoproteins are even more effective emulsifiers than LDL) as well as dispersed emulsifying protein, phosvitin. Yolk granules are so large that they can’t cover a droplet surface very well, but when they’re exposed to moderate concentrations of salt they fall apart into their separate LDLs, HDLs, and proteins, and these are very effective indeed.

Using Eggs to Emulsify Sauces As emulsifiers, egg yolks are most effective when they’re raw, and when they’re warm. Fresh out of the refrigerator, the various yolk particles move only sluggishly and don’t coat the fat droplets as quickly and completely. When yolks are cooked, the proteins unfold and coagulate, thus ending their usefulness as flexible surface coatings. Hard-cooked yolks are sometimes used instead of raw yolks to make emulsified sauces; their disadvantage is that the proteins have been coagulated in place and phospholipids probably trapped in the coagulated particles, so they have far less emulsifying power, and the yolk texture can give a subtle graininess.

And egg whites? They’re a less concentrated source of protein, and designed for a fat-free, watery environment, and therefore of little help in coating fat droplets. However, the white proteins provide some viscosity thanks to their large size and loose associations with each other, so they have some value as emulsion stabilizers.

Oil droplets in mayonnaise. A view through an electron microscope. Protein and emulsifier molecules and aggregates, all from egg yolk, are present between the large droplets and on their surfaces, and help prevent them from coalescing.

Cold Egg Sauces: Mayonnaise

Mayonnaise is an emulsion of oil droplets suspended in a base composed of egg yolk, lemon juice or vinegar, water, and often mustard, which provides both flavor and stabilizing particles and carbohydrates (p. 417). It’s the sauce most tightly packed with oil droplets — as much as 80% of its volume is oil — and is usually dense and too stiff to pour. It can be thinned and flavored with various water-based liquids, including purees and stocks, or it can enrich such liquids the way cream does; it can also be aerated with the addition of whipped cream or egg whites. As a room-temperature preparation, mayonnaise is generally served with cold dishes of various sorts. But thanks to the yolk proteins, it also reacts usefully to heat. It lends body and richness when added to thin broths and briefly cooked; and when layered onto fish or vegetables and broiled, it moderates the heat, puffs up and sets into a rich coating.

Traditionally, mayonnaise is made with raw egg yolks, and therefore carries a slight risk of salmonella infection. Manufacturers use pasteurized yolks, and cooks concerned about salmonella can now find pasteurized eggs in supermarkets. Both vinegar and extra-virgin olive oil kill bacteria, but mayonnaise is best treated as a highly perishable food that should be served immediately or kept refrigerated.

Making Mayonnaise All of the ingredients for making mayonnaise should be at room temperature; warmth speeds the transfer of emulsifiers from the yolk particles to the oil droplet surfaces. The simplest method is to mix together everything but the oil — egg yolks, lemon juice or vinegar, salt, mustard — and then whisk in the oil, slowly at first and more rapidly as the emulsion thickens. However, the cook can produce more stable small droplets by whisking a portion of the oil into just the yolks and salt to start, and then adding the remaining ingredients when the emulsion gets stiff and needs to be thinned. The salt causes the yolk granules to fall apart into its component particles, which makes the yolks become both more clear and more viscous. If left undiluted, this viscosity will help break the oil into smaller droplets.

Though cookbooks often say that the ratio of oil to egg yolk is critical, that one yolk can only emulsify a half-cup or cup of oil, this just isn’t true. A single yolk can emulsify a dozen cups of oil or more. What is critical is the ratio of oil to water: there must be enough of the continuous phase for the growing population of oil droplets to fit into. For every volume of oil added, the cook should provide about a third of that volume in the combination of yolks, lemon juice, vinegar, water, or some other water-based liquid.

A Sensitive Sauce Because mayonnaise is chock-full of oil, so much so that the droplets press up against each other, its emulsion is easily damaged by extremes of cold, heat, and agitation. It will tend to leak oil in near-freezing refrigerators and on hot rather than warm food. These problems are ameliorated in manufactured mayonnaise by the addition of stabilizers, usually long carbohydrate or protein molecules that fill the spaces between droplets. American bottled “salad dressing” is a very stable hybrid of mayonnaise and a boiled white sauce made with water instead of milk. The texture of such modified sauces, however, is noticeably different from the dense, creamy original. Refrigerated mayonnaise should be handled gently, since some oil may have crystallized and escaped from their droplets. If so, stir gently to reemulsify it, perhaps with the addition of a few drops of water.

Making mayonnaise. The cook begins with a small volume of the water phase — mostly egg yolk — and slowly beats oil into droplets in this base (left). As more oil is incorporated, the mixture becomes thicker and the oil is broken into smaller droplets (center). When the sauce is done, as much as 80% of its volume is occupied by oil droplets, and its consistency is semisolid (right).

Hot Egg Sauces:
Hollandaise and Béarnaise

The classic hot egg sauces, hollandaise and béarnaise and their offspring, are egg-emulsified butter sauces. They are similar to mayonnaise in many respects, but of course must be hot to keep the butter fluid. Their dispersed fat phase is usually a smaller proportion of the sauce, between one-and two-thirds of the total volume. Hollandaise and béarnaise differ mainly in seasoning; hollandaise is only lightly flavored with lemon juice, while béarnaise begins with a tart and aromatic reduction of wine, vinegar, tarragon, and shallots.

Heat Thickens — and Curdles The consistency of the hot egg sauces depends on two factors. One is the form and amount in which the butter is incorporated. Whole butter is about 15% water, so each addition thins the egg phase and the sauce as a whole; clarified butter is all butterfat, and thickens the sauce with every addition. The second influence on consistency is the degree to which the egg yolks are heated and thickened. The main trick in making these sauces is to heat the egg yolks enough to obtain the desired thickness, but not so much that the yolk proteins coagulate into little solid curds and the sauce separates. This happens at around 160–170ºF/70–77ºC. A double boiler or a saucepan resting above a larger pan of simmering water will guarantee a gentle and even heat but will also slow the cooking; for this reason, some cooks prefer the riskier but rapid direct heat of a burner. Heating the yolks with the acidic reduction also minimizes curdling; if the pH is around 4.5, the equivalent of yogurt’s acidity, the yolks can be safely heated to 195ºF/90ºC. (The acid causes the proteins to repel each other, so that they unfold before bonding to each other and form an extended network rather than dense curds.) Cooks concerned about salmonella should make sure the yolks are cooked at least to 160ºF/70ºC, or else should use pasteurized eggs.

Making Hollandaise and Béarnaise There are at least five different ways of making hollandaise and béarnaise, each with its advantages and disadvantages.

• Cook the egg and water-based ingredients first to a thick consistency, then whisk in pats of whole butter to emulsify the butterfat and thin the continuous phase. This is Carême’s method, and is the trickiest because the small volume of the initial egg mixture is easily overcooked.
• Warm the yolks and water-based ingredients, whisk in either whole or clarified butter, then cook the mixture until it reaches the desired consistency. This is Escoffier’s method, and has the advantage that the cook can control the final consistency directly, and by heating the entire volume of sauce.
• Put all of the ingredients for the sauce in a cold saucepan, turn the heat on low, and start stirring. The butter gradually melts and releases itself into the egg phase as both heat up together, and the cook then continues to heat the formed sauce until it reaches the desired consistency. This is the simplest method.
• Don’t cook the yolks at all; just warm them and the water-based ingredients above the melting point of butter, then whisk clarified butter in until the crowding of droplets creates the desired consistency. This is essentially a butter mayonnaise, and eliminates the possibility of overcooking the yolks.
• Make the butter-sauce version of a sabayon (p. 639). Whisk the egg yolks and some water while heating them until they form an airy foam, and then gently incorporate melted or clarified butter and the lemon juice or acid reduction. This version is of course much lighter, and is also made with less butter per yolk.

It’s possible to make hot egg sauces with fats and oils other than butter, and to flavor the water phase with meat reductions or vegetable purees.

Holding and Salvaging Hot Egg Sauces Butter sauces need to be kept warm to prevent the butter from solidifying, and are best held at around 145ºF/63ºC to discourage the growth of bacteria. Because the egg proteins slowly continue to bond to each other at this temperature, the cook should stir the sauce occasionally to keep it from thickening. The container should be covered to prevent the sauce’s moisture from evaporating and overcrowding the fat droplets, and to prevent the formation of a protein skin on the surface.

Curdled egg sauces can be rescued by straining out the solid bits of protein, keeping the whole mess warm, beginning with another warm egg yolk and one tablespoon/15 ml water, and slowly whisking the sauce into the new yolk. The same technique will revive a sauce that has been refrigerated and so had its butterfat crystallized; the crystals melt to form fat puddles when the sauce is simply rewarmed.

Vinaigrettes

A Water-in-Oil Emulsion The most commonly and easily made emulsified sauce is the simple oil-and-vinegar salad dressing known as vinaigrette, from the French word for “vinegar.” Vinaigrette does a good job of clinging to lettuce leaves and other vegetables, and lending a refreshing tart counterpoint to their taste. The standard proportions for a vinaigrette are 3 parts oil to 1 vinegar, similar to the proportions in mayonnaise, but the preparation is much simpler. The liquids and other flavorings — salt, pepper, herbs — are often simply shaken into a cloudy, temporary emulsion at the last minute, then poured onto and mixed with the salad. When made in this casual way, a vinaigrette is the odd sauce out: instead of being oil droplets dispersed in water, it’s water (vinegar) droplets dispersed in oil. Without the help of an emulsifier, one part of water simply cannot accommodate three parts of oil, so the more voluminous phase, the oil, becomes the continuous phase.

There are good reasons for making oil the continuous phase of a vinaigrette, and for not worrying about the stability of the emulsion. Where many sauces are served under or atop large pieces of food, oil-and-vinegar emulsions are used almost exclusively as salad dressings, whose role is to provide a very fine and even coat for the extensive surface area of lettuce leaves and cut vegetables. A thin, mobile sauce is more effective at this than a thick, creamy one, and oil adheres to the vegetable surfaces better than the water-based vinegar, whose high surface tension causes it to bead up rather than leave a film. And because the sauce is so spread out, it doesn’t matter as much that the dispersed droplets be carefully stabilized. Because water and oil are antagonists, the salad fixings should be well dried before they’re tossed with vinaigrette; surfaces wet with water will repel the oil.

Making a vinaigrette dressing. The proportion of oil to the water phase in a vinaigrette is similar to the proportion in mayonnaise, but in a vinaigrette the water is the phase dispersed in droplets, and the oil is the continuous phase. This emulsion is much less crowded with droplets, and accordingly a vinaigrette is more fluid than mayonnaise.

Untraditional Vinaigrettes Nowadays the term vinaigrette is used very broadly to mean almost any kind of emulsified sauce enlivened with vinegar, whether water-in-oil or oil-in-water, cold or hot, destined for salads or vegetables or meats or fish. You can make an oil-in-water version simply by changing the proportions: reducing the oil content and diluting the vinegar with other watery ingredients to provide more of the continuous phase without excessive acidity. Creamy but thin oil-in-water vinaigrettes can spread and cling reasonably well, and have the advantage over a classic vinaigrette of being slower to discolor and wilt lettuce leaves. (Oil seeps through breaks in the waxy leaf cuticle and spreads into the leaf interior, where it displaces air and causes the leaf to darken and its structure to collapse.)

Inventive cooks now make vinaigrettes with a variety of fats, including flavorsome olive and nut oils, neutral vegetable and seed oils, melted butter, and even hot meat and poultry fats (pork, duck); the water phase may contain vegetable or fruit juices or purees, meat juices or stock reductions; and the droplets may be emulsified or stabilized by thorough pulverizing to a small size in a blender, or with pounded herbs or spices, vegetable purees, mustard, gelatin, or cream. Today’s vinaigrette is a very versatile kind of sauce!

Bottled salad dressings that look like vinaigrettes are generally stabilized and given body with starch or carbohydrate gums, which in low-fat versions can produce a slimy consistency.

Sauces Thickened
with Bubbles: Foams

Like emulsions, foams are a dispersion of one fluid in another. In the case of foams, the fluid is not a liquid, but a gas, and the dispersed particles are not droplets, but bubbles. Still, the bubbles do the same thing that droplets do in a sauce: they get in the way of water molecules in the sauce, prevent them from flowing easily, and thus give the sauce as a whole a thicker body. At the same time, they provide two unique characteristics: a large surface area in contact with air that can enhance the release of aromas to the nose; and a light insubstantiality and evanescence that offers a refreshing contrast to the texture of nearly any food they accompany.

There’s one classic foam sauce, the sabayon, which is made by cooking and whipping egg yolks at the same time to form a stable mass of bubbles. And both whipped cream and whipped egg whites can be folded with their bubbles into any water-based sauce. But cooks nowadays make foams from all kinds of water-based liquids and semisolids that contain dissolved or suspended or structure-stabilizing molecules of some kind. The Catalan chef Ferran Adrià pioneered this development, with foams of — among other ingredients — cod, shellfish, foie gras, asparagus, potatoes, raspberries, and cheese. Cooking broths and their reductions, protein-and starch-thickened sauces, juices, purees, and emulsified sauces can all be lightened by incorporating bubbles into them. And it’s a quick last-minute preparation: just agitate some of the liquid until it froths, then scoop off the bubble-rich portion, add it to the food, and serve.

Making and Stabilizing Foams

There are several different ways of getting bubbles into a liquid and stabilizing them. Whipping with a whisk or hand-heldblender introduces air by agitating the liquid surface; the foaming wands on espresso machines shoot steam, a mixture of water vapor and air; and foaming devices for whipped cream and seltzer water mix a stream of pressurized carbon dioxide or nitrous oxide with the liquid. Any dissolved or suspended molecules in the liquid collect at the interface of the air and liquid and give the bubble wall some solid reinforcement.

However, the reinforcement will be momentary and the bubbles short-lived unless the molecules can form a stable layer at the interface. This is exactly what emulsifiers like lecithin and proteins do, and for the same reason that they stabilize oil droplets in emulsions: they have a water-soluble portion that rests in the bubble wall, and a water-insoluble portion that rests in the air. Because the bubbles in a typical foam are between 0.1 and 1 millimeter across, much larger than most emulsion droplets, they require very little emulsifier to cover their surface area, typically just 0.1% of the liquid weight (1 gram per quart or liter).

Stabilizing Foams A liquid that is even modestly supplied with proteins or yolk phospholipids will form an impressive mass of bubbles, solid enough to stand up without flowing or even slumping. However, the foam may still collapse within a minute or two. Air and water have very different densities, so when the foam is left to stand on its own, the air bubbles rise while gravity pulls the liquid in their walls in the opposite direction. This means that liquid drains from the bubble walls, which also lose water to evaporation. Eventually, the foam at the surface becomes dry, around 95% air and just 5% liquid, the bubble walls become too thin, fail, and the bubbles pop.

This instability of the foam as a whole can be prevented by the same materials that stabilize the emulsified sauces: namely materials that interfere with the free movement of water molecules, and thereby slow the drainage and thinning of the bubble walls. Foam stabilizers include the microscopic particles in purees, proteins, thickening carbohydrates like starch, pectin, and gums — and even emulsified fat. Free fat or oil is a foam killer, because the fat spreads at the interface with the air — it’s chemically more compatible with air than with water — and prevents emulsifiers from settling at the interface and stabilizing it. However, if the fat is emulsified — for example in an egg yolk or yolk-based sauce — then it remains dispersed in the water phase, and its droplets only interfere with the flow of liquid from the bubble walls.

Heat-Stabilized Foams: Sabayons Both the method and the name of the French sabayon derive from the Italian zabaglione, a sweet, winy foam of egg yolks (p. 113). Though rich in proteins and phospholipids, egg yolks don’t foam well on their own because they don’t contain enough water. Add water and beat and they foam prodigiously but temporarily; heat while beating and the yolk proteins unfold and bond to each other into a thickening, stabilizing network. This is how sabayons are made, with the water replaced by a flavorful liquid of some some sort, a broth or juice or puree for example. The hot egg-emulsified butter sauces can be made in the style of a sabayon, with the butter folded in gently at the end so as not to pop too many of the foam bubbles. (The butter doesn’t need to be beaten in because the foam has created a large surface area over which the butter can spread and stay suspended, much as a vinaigrette is spread over lettuce leaves.) The proteins in aerated yolks thicken around 120ºF/50ºC, and may coagulate and separate if heated much above that, so many cooks prepare sabayons over a pot of hot water rather than over direct stovetop heat.

Salt

The word sauce comes via Latin from anancient root word meaning “salt,” the primordial condiment that was prepared by the earth billions of years before early humans learned to enliven their foods with it. Salt is an important flavoring, but also much more than that, and is an ingredient in nearly every preparation described in this book. The relevant chapters explain its role in the making of such foods as cheese, cured meats and fish, pickled vegetables, boiled vegetables, soy sauce, and bread. Here are a few pages about salt itself.

The Virtues of Salt Salt is like no other substance we eat. Sodium chloride is a simple, inorganic mineral: it comes not from plants or animals or microbes, but from the oceans, and ultimately from the rocks that erode into them. It’s an essential nutrient, a chemical that our bodies can’t do without. It’s the only natural source of one of our handful of basic tastes, and we therefore add it to most of our foods to fill out their flavor. Salt is also a taste enhancer and taste modifier: it strengthens the impression of aromas that accompany it, and it suppresses the sensation of bitterness. It’s one of the very few ingredients that we keep in pure form at the table, to be added to individual taste as we eat.

In addition to sauces and salads, somewhat bitter leaves dressed to make them more palatable, another food named for salt is sausage, one of the preparations in which salt is more than just a flavoring. Thanks to its basic chemical nature, salt can alter other ingredients in useful ways. Sodium chloride dissolves in water into separate single atoms that carry electrical charge — positively charged sodium ions and negatively charged chloride ions. These atoms are smaller and more mobile than any molecule, and therefore readily penetrate our foods, where they react in useful ways with proteins and with plant cell walls. And because a concentrated solution of any kind draws water out of living cells by osmosis — water in the less concentrated cell fluid moves out of the cell to relieve the imbalance — the presence of sufficient salt in a food discourages the growth of spoilage bacteria while allowing harmless flavor-producing (and salt-tolerant) bacteria to grow. It thus preserves the food and improves it at the same time.

Salt is a remarkable ingredient. No wonder that people from earliest times have found it indispensable, that it’s embedded in everyday words and sayings (salary, from the Roman practice of paying soldiers in salt; worth his salt; salt of the earth), and that it has been the occasion for governmental monopolies and taxes and popular revolts against them, from revolutionary France to Gandhi’s 1930 salt march to Dandi.

Salt Production

People have been gathering crystalline salt since prehistoric times, both from the seacoasts and from inland salt deposits. The rock-salt deposits, some of which are hundreds of millions of years old, are masses of sodium chloride that crystallized when ancient seas were isolated by rising land masses and evaporated, and their beds then covered over by later geological processes. Until the 19th century, salt was produced mainly for the preservation and flavoring of foods. Nowadays large amounts are used in industrial manufacturing of all kinds, as well as in the de-icing of winter roads, and salt production itself has been industrialized. Most rock salt is now mined by solution, or pumping water into the deposits to dissolve the salt, then evaporating the brine down in vacuum chambers to form solid crystals. While some sea salt is still produced by gradual solar evaporation from open-air salt pans in sufficiently warm, dry regions, much is now produced by more rapid vacuum evaporation.

Removing Bitter Minerals Salt comes from seawater, and seawater contains significant quantities of several bitter minerals, the chloride and sulfate salts of magnesium and calcium. Producers have a couple of ways of dealing with these minerals. They can remove them from rock salt by dissolving the salt, then adding sodium hydroxide and carbon dioxide to the brine to precipitate magnesium and calcium. They can remove them from seawater by the same means, or else by slow and gradual concentration in open-air pans, during which the calcium salts become insoluble, crystallize, and settle before the sodium chloride does, and so can be separated. The sodium chloride in turn crystallizes before the magnesium salts, whose slight residue on the crystal surfaces can then be washed off in new brine.

Crystal Shapes These days both edible rock salt and sea salts are produced from brines by evaporating the water away. The evaporation process determines the kinds of salt crystals produced. If the brine becomes concentrated rapidly in a closed tank and crystallization takes place throughout the brine, then many small, regular cubic crystals are formed: the familiar granulated salt of the salt shaker. However, if the evaporation proceeds slowly and at least partly in an open container or sea-side pool, so that crystallization occurs primarily at the brine surface, then the salt solidifies into fragile, hollow, pyramid-shaped flakes, a useful shape for sticking to the surfaces of baked goods, and for dissolving rapidly. To be preserved, the flakes must be scooped off the surface before they settle and sink into the brine, where they fill in and become the large, coarse crystal often seen in minimally processed sea salts.

Once collected and dried, both granular and flake salts can be rolled, compacted, and crushed to make various particle sizes and shapes.

Kinds of Salt

Worldwide, about half of all salt production comes from the sea, and about half from salt mines; in the United States, 95% is mined. Depending on how they’ve been processed, edible salts range from 98 to 99.7% sodium chloride, with the lower figures typical of table salts treated with anticaking additives.

Granulated Table Salt Granulated table salts come in the form of small, regular, cubic crystals, are the densest salts, and take the longest to dissolve. Standard table salt is often supplemented with additives, as much as 2% of the total weight, that prevent the crystal surfaces from absorbing moisture and sticking to each other. These additives include aluminum and silicon compounds of sodium and calcium, silicon dioxide — the material of glass and ceramics (p. 788) — and magnesium carbonate. Other compounds called humectants may be added to keep these additives from excessive drying and caking. Most anticaking additives do not dissolve as readily as salt, and cloud the brines for pickled vegetables, so specialized pickling salts omit them. These additives may also contribute slight undesirable tastes of their own.

Iodized Salt Many granulated table salts and some sea salts are fortified with potassium iodide to help prevent devastating iodide deficiency (below). This practice began in the United States in 1924. Because iodide is sensitive to acidity, manufacturers usually supplement iodized salt with stabilizing traces of sodium carbonate or thiosulfate and sugar. When dissolved in chlorinated tap water, iodized salt can develop a distinct seaweed-like iodine odor, the result of a reaction between the iodide and chlorine compounds.

Flake Salt Flake salts come in flat, extended particles rather than compact, dense granules. Flake salts are produced by surface evaporation of the mother brine, or by mechanically rolling granulated salts. Maldon sea salt from the south coast of England includes individual hollow-pyramid crystals measuring as much as a half-inch/1 cm across. The large particles of flake salts and minimally processed sea salts are easier to measure and add by the pinch. Sprinkled onto a food at the last minute, flake salt provides a crunchy texture and a burst of flavor. The flat crystals don’t pack together as compactly as cubic crystals, so a given volume measure of flake salt weighs less than the same measure of granulated salt.

Kosher Salt Kosher salt is salt used for the koshering process, the preparation of meats according to Jewish dietary laws (p. 143). It comes in coarse particles, often flakes, and is sprinkled on the freshly butchered meat for the purpose of drawing out blood. Because it’s meant to remove impurities, the salt itself is not iodized. Many cooks like to use kosher salt in general cooking for its relative purity and ease of dispensing by hand.

Unrefined Sea Salt Unrefined sea salts are produced in the way that agricultural crops are: their beds are managed and tended, the salt is harvested when ready, and minimally processed. The tending consists of a slow progressive concentration of the seawater, and can take as much as five years. In most places the freshly harvested salt is washed of its surface impurities before drying. Unrefined versions are not systematically washed of their coating of minor minerals, algae and a few salt-tolerant bacteria. They therefore carry traces of magnesium chloride and sulfate and calcium sulfate, as well as particles of clay and other sediments that give the crystals a dull gray cast (unrefined French salts are called sel gris, “gray salt”). Because taste and aroma compounds are often detectable in minute concentrations, and these salts include both organic and mineral impurities, it’s possible that they would have a more complex flavor than refined salts, though that complexity would be overwhelmed by any food to which the salt is added.

Fleur de sel Fleur de sel, literally “flower of salt,” meaning the finest and most delicate, is a special product of the sea-salt beds of west-central France. It consists of the crystals that form and accumulate at the surface of the salt pans when the humidity and breezes are right; they’re gently raked off the surface before they have a chance to fall below the surface, where the ordinary gray sea salt accumulates. Fleur de sel forms delicate flakes, doesn’t carry the particles of sediment that darken and dull the gray salt, but is said to carry traces of algae and other materials that contribute a characteristic aroma. This is possible, since the interface between water and air is where aroma molecules and other fatty materials would concentrate; but to date the aroma of sea salts has not been much studied. Thanks to the labor required to make it, fleur de sel is expensive, and is used as a last-minute condiment rather than as a cooking salt.

Flavored and Colored Salts In addition to providing its own saltiness, salt is sometimes turned into a carrier for other flavors and for decorative colors. Examples of flavored salts include celery salt with ground celery seeds, garlic salt with dehydrated garlic granules, and the smoked and roasted salts found in Wales, Denmark, and Korea. The “black salt” of India, more of a gray-pink when ground, is an unrefined mixture of minerals with a sulfurous smell. Black and red Hawaiian salts are made by mixing ordinary sea salt with finely ground lava, clay, or coral.

Salt and the Body

Salt and Blood Pressure Sodium and chloride ions are essential components of the system that keeps our general body chemistry in working balance. They mostly remain in the fluid that surrounds all our cells, the plasma, the fluid portion of the blood, where they balance the potassium and other ions inside the cells. It’s estimated that we need something like 1 gram of salt per day, a requirement that goes up with physical activity since we lose body fluids and minerals in sweat. Thanks to its presence in nearly all manufactured foods, the average daily salt intake in the United States is around ten times the requirement.

Medical scientists have long suspected that constant excessive salt intake results in an excessive volume of plasma being contained in our blood vessels, and therefore causes high blood pressure, which damages the blood vessels and increases the risk of heart disease and stroke. However, low-salt diets have been found to lower high blood pressure only modestly, and only in some people. And low-salt diets have surprising side effects of their own, including undesirable increases in blood cholesterol levels. At this time, it appears that the most beneficial nonmedical influences on blood pressure are general dietary balance — more vegetables, fruits, and seeds rich in potassium, calcium, and other minerals — together with physical exercise that conditions the whole cardiovascular system.

Effects on Kidneys, Bones, and the Digestive System Excess sodium is absorbed from the blood and excreted by the kidneys, which help regulate many body systems. High sodium levels thus have the potential for having indirect effects on those systems. There’s evidence that they can cause loss of bone calcium and thus increase our dietary calcium requirement, as well as worsening chronic kidney disease.

Though our bodies have ways of diluting and excreting excessive doses of salt, eating salty foods exposes the surfaces of our digestive system to potentially cell-damaging concentrations. There is evidence from China and elsewhere in Asia that diets high in salt increase the risk of several cancers of the digestive system.

Iodized Salt Some salts do carry an undisputed health benefit. Iodized salts include trace amounts of potassium iodide, and thus are a source of a mineral that’s essential for proper functioning of the thyroid gland, which regulates the body’s heat production, protein metabolism, and development of the nervous system. Iodine is a chemical relative of chlorine and readily found in ocean fish, seaweeds, and crops and animals raised near the seacoast. Iodine deficiency was once common in inland areas, and is still a significant problem in rural China. It causes both physical and mental impairment, especially in children.

Salt to Taste: Salt Preference Both the sensitivity to salt and the preference for saltiness in foods vary a great deal from person to person. They depend on several factors, including inherited differences in the numbers and effectiveness of taste receptors on the tongue, general health, age, and experience. Most young adults can identify as salty a water solution with 0.05% salt, or 1 teaspoon in 10 quarts/liters, while people older than sixty years generally detect saltiness only at double that concentration. Many manufactured soups, which many people experience as moderately to very salty, are around 1% salt (10 grams, or 2 teaspoons per quart/liter), approximately the same concentration as our blood plasma. Some may be 3% salt, which is the average salinity of seawater.

It appears that the basic liking for saltiness is innate in humans, no doubt because salt is an essential nutrient. The preference for a certain level of saltiness is learned through repeated eating experiences and the expectations they create in us. Preferences can be changed by constant exposure to different salt levels, which changes expectations. But this takes time, usually two to four months.