The Making of Fruit: Ripening

Before Ripening: Growth and Expansion

The Work of Ethylene and Enzymes

Two Styles of Ripening, Two Ways of Handling

Common Fruits of Temperate Climates: Apple and Pear, Stone Fruits, Berries

Pome Fruits: Apple, Pear, and Relatives

Stone Fruits: Apricot, Cherry, Peach, and Plum

Berries, Including Grapes and Kiwi Fruit

Other Temperate Fruits

Fruits from Warm Climates: Melons, Citrus Fruits, Tropical Fruits, and Others

Melons

Fruits from Arid Climates: Fig, Date, and Others

The Citrus Family: Orange, Lemon, Grapefruit, and Relatives

Some Common Tropical Fruits

The vegetables described in chapter 6 are mainly plant parts with either mild, accidental flavors (roots, leaves, stalks) or strong defensive ones (the onion and cabbage families). We usually cook them, because cooking improves their flavor and makes them softer and easier to eat. The fruits described in this chapter are parts that the plant creates in order to attract animals to eat them and disperse the seeds within them. So the plant fills these fruits with a mouthwatering mixture of sugars and acids, endows them with pleasant aromas and eye-catching colors, and softens them for us: they’re delicious and beautiful even when raw. The box on pp. 382–383 summarizes the essential flavor elements of some common fruits, especially the balance between sweet and sour that provides their taste foundation.

The Making of Fruit:
Ripening

Among all our foods, fruits are unique in the way that they progress from inedibility to deliciousness. Immature vegetables and young meat animals are at their tenderest and most delicate, but immature fruits are usually at their least appealing. We may still eat and enjoy them — green tomatoes, green papayas, green mangoes — but we treat them as vegetables, cut them small for a salad or cook or pickle them. In order to graduate from vegetablehood, fruits must undergo the process called ripening, which creates their distinctive character.

Before Ripening:
Growth And Expansion

A fruit is a distinct organ that develops from the flower, and in particular from the flower’s female tissue, the ovary, which encloses the plant’s maturing seeds. Most fruits are simply the thickened ovary wall, or else they incorporate nearby tissues as well. Apples and pears, for example, are made up mainly of the stem tip in which the flower parts are embedded. The fruit usually develops into three distinct layers: a thin outer protective skin, a thin inner protective coat around the central mass of seeds, and a thick, succulent, flavorful layer in between.

Fruit goes through four distinct stages of development. The first is usually fertilization of the female ovule by male pollen, which initiates the production of growth-promoting hormones and so leads to the expansion of the flower’s ovary wall. Some conveniently seedless fruits, including bananas, navel oranges, and some grapes, manage to develop without fertilization. The second, relatively brief stage of fruit development is the multiplication of cells in the ovary wall, which in the tomato is virtually complete at the moment of fertilization (you can see the fully formed but tiny fruit at the base of the flower as soon as it opens).

Most of the noticeable growth during fruit development takes place during the third stage, the expansion of the storage cells. This growth can be remarkable. Melons at their most active put on better than 5 cubic inches/80 cc a day. Most of this expansion is due to the accumulation of water-based sap in the cell vacuoles. Mature fruit storage cells are among the largest in the plant kingdom, in watermelons approaching a millimeter in diameter. During this growth stage, sugar is stored in the cell vacuole as is or in more compact granules of starch. Defensive compounds, among them poisonous alkaloids and astringent tannins, accumulate in the cell vacuoles to deter infection or predation, and various enzyme systems are readied for action. When the seeds become capable of growing on their own and the fruit is ready to attract animals to disperse them, the fruit is said to be mature.

The Work of Ethylene
and Enzymes

The final stage of fruit development is ripening, a drastic change in the life of the fruit that leads to its death. It consists of several simultaneous events. Starch and acid levels decrease, and sugars increase. The texture softens; defensive compounds disappear. A characteristic aroma develops. Skin color changes, usually from green to a shade of yellow or red. The fruit thus becomes sweeter, softer, and tastier, and it advertises these improvements visually. Because ripening soon gives way to rot-ting, ripening was long considered to be an early stage in the fruit’s general disintegration. But it’s now clear that ripening is a last, intense phase of life. As it ripens, the fruit actively prepares for its end, organizing itself into a feast for our eye and palate.

Fruits: Their Potential for Improvement after Harvest, and Optimal Storage Temperatures

Most of the changes in ripening are caused by a host of enzymes, which break down complex molecules into simpler ones, and also generate new molecules just for this moment in the fruit’s life. There is a single trigger that sets the ripening enzymes into action. The first clues to its identity came around 1910. From the Caribbean islands came a report that bananas stored near some oranges had ripened earlier than the other bunches. Then California citrus growers noticed that green fruit kept near a kerosene stove changed color faster than the rest. What secret ripening agent did stove and fruit have in common? The answer came two decades later: ethylene, a simple hydrocarbon gas produced by both plants and kerosene combustion, which triggers ripening in mature but unripe fruit. Much later, scientists found that fruits themselves produce ethylene well in advance of ripening. It is thus a hormone that initiates this process in an organized way.

Two Styles of Ripening,
Two Ways of Handling

There are two different styles of ripening among fruits. One is dramatic. When triggered by ethylene, the fruit stimulates itself by producing more ethylene, and begins to respire — to use up oxygen and produce carbon dioxide — from two to five times faster than before. Its flavor, texture, and color change rapidly, and afterwards they often decline rapidly as well. Such “climacteric” fruits can be harvested while mature but still green, and will ripen well on their own, especially if nudged by an artificial dose of ethylene. They often store their sugars in the form of starch, which enzymes convert back into sweetness during the post-harvest ripening.

The other style of ripening is undramatic. “Nonclimacteric” fruits don’t respond to ethylene with their own escalating ethylene production. They ripen gradually, usually don’t store sugars as starch, and so depend on their connection to the parent plant for continued sweetening. Once harvested, they get no sweeter, though other enzyme actions may continue to soften cell walls and generate aroma molecules.

These basic styles of ripening determine how fruits are handled in commerce and in the kitchen. Climacteric fruits like bananas and avocados, pears and tomatoes can be picked mature but still hard to minimize physical damage, packed and shipped to their destinations, then gassed with ethylene to ripen them for the produce bin. Consumers can hasten the process by enclosing the fruits in a paper bag with a ripe fruit (plastic traps too much moisture) to expose them to an active ethylene emitter and concentrate the ethylene gas in the air around them. Nonclimacteric fruits like pineapples, citrus fruits, most berries, and melons don’t store starch or improve markedly after harvest, so their quality depends mainly on how far they had ripened on the plant. They’re best when picked and shipped as ripe as possible, and there’s nothing consumers can do to influence their quality: we simply have to choose good ones in the first place.

With just a few exceptions (pears, avocados, kiwis, bananas), even climacteric fruits will be much better if they’re allowed to ripen on the plant, from which they can continue to accumulate the raw materials of flavor until the harvest.

Common Fruits of Temperate
Climates: Apple and Pear,
Stone Fruits, Berries

Pome Fruits: Apple, Pear,
and Relatives

Apples, pears, and quinces are closely related members of the rose family, natives of Eurasia that were domesticated in prehistoric times. They are a kind of fruit known as a pome (from the Latin for “fruit”). The fleshy portion of a pome fruit is the greatly enlarged tip of the flower stem. The remains of the flower project from the bottom of the fruit, and the few small seeds are protected in a tough-walled core. Apples and their relatives are climacteric fruit, and contain starch stores that can be turned into sugar after harvest. They generally keep well in cold storage, though late-harvested fruit tend to develop brown cores. Apples are generally sold ripe and keep best if immediately wrapped and refrigerated; pears are sold unripe and are best ripened at relatively cool room temperatures, then refrigerated without close wrapping.

The reddish colors of pome fruits (usually in the skin but sometimes in the flesh) are due mainly to water-soluble anthocyanin pigments, their yellow and cream colors to fat-soluble carotenoids, including beta-carotene and lutein (pp. 257, 267). These fruits are good sources of phenolic antioxidant compounds (p. 267), particularly simple ones (chlorogenic acid, also found in coffee), which are especially concentrated in the skin. Some apples have an antioxidant activity equivalent to the vitamin C in 30 equal portions of orange!

Apples and pears owe their primary flavors to characteristic esters (see box, p. 355). The flavors of pome fruits differ among varieties, among fruits on different parts of a single tree, and even within a single fruit, from top to bottom and from the core outwards. Pears are often noticeably more flavorful at the flower end than at the stem end. Both apples and pears contain an indigestible, slightly sweet sugar alcohol, sorbitol (0.5%), so a large helping of cider can cause the same discomfort as do inulin-rich foods (p. 307).

Apples Apple trees are especially hardy and are probably the most widely distributed fruit trees on the planet. There are 35 species in the genus Malus. The species that gives us most of our eating apples, Malus x domestica, seems to have originated in the mountains of Kazakhstan from crossings of an Asian species (Malus sieversii) with several cousins. The domesticated apple spread very early through the Middle East. It was known in the Mediterranean region by the time of the Greek epics, and the Romans introduced it to the rest of Europe. These days apple production is an international enterprise, with southern hemisphere countries supplementing northern stored apples during the off-season, and common varieties as likely to have come from Asia (e.g., Fuji, from Japan) as from the West. There are several thousand named apple varieties, which can be divided into four general groups.

Pome fruits and the flower from which they arise. The edible portion of apples and pears derives from the flower base, or receptacle. Because the ovary is set below most of the flower parts, the flower remains a scar at the bottom of the fruit.

• Cider apples (mainly the European native Malus sylvestris) are high-acid fruits rich in astringent tannins, qualities that help control the alcoholic fermentation and clarify the liquid (tannins cross-link protein and cell-wall particles and cause them to precipitate). They’re used only in cider making.
• Dessert or eating apples are crisp and juicy, and have a pleasing balance between sour and sweet when eaten raw (pH 3.4, 15% sugar), but become relatively bland when cooked. Most of the apples in supermarkets and produce markets are dessert apples.
• Cooking apples are distinctly tart when raw (a pH around 3 and sugar content around 12%), well-balanced when cooked, and have a firm flesh that tends to maintain its structure when heated in pies or tarts, rather than falling immediately into a puree or — as in some early “codling” varieties — into a fluffy froth. Many countries have traditionally had their standard cooking apples (France its Calville blanc d’hiver, England its Bramley’s Seedling, Germany its Glockenapfel for strudel). But these are being replaced by dual-purpose varieties.
• Dual-purpose apples are adequate either raw or cooked (e.g., Golden Delicious, Granny Smith). These are usually at their best for cooking when young and tart, best for eating when older and more mellow.

An apple’s potential for cooking can be tested by wrapping a few slices in aluminum foil and baking in a hot oven for 15 minutes, or microwaving a few slices wrapped in plastic film until the film balloons with steam.

Apple Flavor Apple varieties can have very distinctive flavors, and these evolve even after the fruit are picked from the tree. The English were great connoisseurs a century ago, and Edward Bunyard wrote that by storing apples properly in a cool place and tasting them periodically, the apple lover could “catch the volatile ethers at their maximum development, and the acids and sugars at their most grateful balance.” Apples do become more mellow with time because they consume some of their malic acid for energy. Much of their aroma comes from the skin, where volatile-creating enzymes are concentrated. The distinctive aroma of cooked apple pulp comes largely from a floral-smelling fragment of the carotenoid pigments (damascenone).

Apple Air and Texture Apples differ from pears in having as much as a quarter of their volume occupied by air, thanks to open spaces between cells in the fruit. (Pears are less than 5% air.) The air spaces contribute to the typical mealiness of an overripe apple: as the cell walls soften and the cell interiors dry out, biting into the apple simply pushes the largely separated cells apart from each other rather than breaking the cells and releasing pent-up juices. Air cells become a factor in baking whole apples; they fill with steam and expand as the apple cooks, and the skin will split unless a strip is removed from the top to release the pressure.

Both apples and crabapples are good sources of cell-wall pectins (p. 265) and make excellent jellies. For the same reason, a simple puree of apples has a thick, satisfying consistency when briefly cooked into apple-sauce, or slowly reduced to “apple butter.”

Apple Juice and Cider Apple juice can be either opalescent or clear depending on whether its pectins and proteins are left intact to deflect light rays. Made fresh, it will stay pale and retain its fresh flavor for about an hour, after which the darkening and aroma-modifying influences of enzymes and oxygen become evident. Browning can be minimized by heating the juice rapidly to the boil to inactivate the browning enzymes, but of course this lends a cooked flavor to the juice. Pasteurized apple juice was first manufactured around 1900 in Switzerland, and is now one of the most important commercial fruit products in the United States. Cider is still an important product in northwest Spain, western France, and England, where the traditional method was to let the fruit pulp ferment slowly through the cold winter, reaching an alcohol content around 4%.

Pears Pears are fruit of the genus Pyrus, more temperamental to grow than the apple and less common, but called by some “the queen of fruit” for their refinement of flavor, texture, and shape. Pears are less tart than apples, and denser. The familiar elongated European pears, with mostly smooth flesh, are varieties of the west Asian Pyrus communis. “Asian pears” are varieties of two species native to China but intensively improved in Japan, P. pyrifolia and P. ussuriensis. They have a juicy but crisp flesh, more or less gritty with cellulose-rich “stone cells,” and may be elongated or apple-shaped. The characteristic aroma of pears comes from several esters, including the “pear ester” (ethyl decadienoate).

Some Distinctive Apple Flavors and Varieties

Flavor

Varieties

Simple, refreshing

Gravenstein, Granny Smith

Strawberry, raspberry

Northern Spy, Spitzenburg

Winey

McIntosh (well matured)

Aromatic and flowery

Cox’s Orange and Ribston Pippins

Honey

Golden Delicious (well matured), Fuji, Gala

Anise or tarragon

Ellison’s Orange, Fenouillet

Pineapple

Newtown Pippin, Ananas Reinette

Banana

Dodds

Nutty

Blenheim Orange

Nutmeg

D’Arcy Spice

In general, pears have a higher respiratory rate than apples and don’t store as well. They’re unique among temperate fruits in being of the highest quality when picked mature but still hard and ripened off the tree; picked after ripening begins, their texture becomes mushy and their core breaks down. They will also develop a mealy core if excessively warmed after cold storage. They’re best ripened slowly over several days at between 65–68ºF/18–20ºC. Pears are sensitive to carbon dioxide, so they shouldn’t be enclosed in plastic bags at any stage. Asian pears are especially prone to bruising and are often marketed in protective sleeves.

Pear Varieties Originally, all pears were gritty “sand pears” and hard-fleshed. Centuries of breeding greatly reduced the prominence of gritty stone cells (but not in varieties for making perry, the pear version of cider, where they’re valued for helping to grind the flesh before fermentation). The soft “butter” texture characteristic of many European pears was developed in the 18th century by Belgian and French breeders. European pears are classified in three groups according to when they’re harvested and their traditional storage life (now extended by controlled atmospheres and temperatures). Summer pears like the Bartlett (also called Williams or Bon chretien) are harvested in July and August and keep for one to three months; autumn pears like the Bosc and Comice are harvested in September and October and keep two to four months; and winter pears like the Anjou and Winter Nellis are harvested in October and November and keep six to seven months.

Quince Quinces, fruit of the central Asian tree Cydonia oblonga, give us a taste of what apples and pears might have been like in their primitive form. They are gritty with stone cells, astringent, and hard even when ripe. But they have a distinctive, flowery aroma (thanks to lactones and violet-like ionones, all derived from carotenoid molecules) that’s especially concentrated in the fuzzy yellow skin. And cooking domesticates them: heat breaks down and softens their pectin-rich cell walls, and the astringent tannins become bound up in the debris, so the taste softens as well. Quince paste firm enough to slice is a traditional product of Spain (membrillo) and Italy (cotognata), and in Portugal a quince preserve was the original marmalade (marmalada). The 16th-century alchemist and confectioner Nostradamus gave several recipes for quince preserves and observed that cooks “who peel them [before cooking] don’t know why they do this, for the skin augments the odor.” (The same is true for apples.)

Quinces have another enchanting quality: when slices are slowly cooked in sugar over several hours, they turn from a pale off-white to pink to a translucent, deep ruby red. The key to this transformation is the fruit’s store of colorless phenolic compounds, some of which cooking turns into anthocyanin pigments (p. 281). Pears contain the same compounds, but in smaller quantities (common Bartletts about a twenty-fifth, Packhams a tenth to a half), and so usually get pink at best.

Medlar Medlars are small fruits of an apple relative (Mespilus germanica) native to central Asia, now rare but once commonly grown in Europe as a winter fruit. Like the quince, the medlar remains hard and astringent even when ripe, so it keeps well and even improves if left on the tree through early frosts. It was made into preserves, but more often it was “bletted” (a 19th-century coinage from the French blessé, “bruised”), or picked from the tree and kept in a cool, dry place for several weeks until the enzymes in its own cells digest it from within, and its flesh turns soft and brown. The astringency disappears, the malic acid is used up, and the aroma develops strong overtones of spice, baked apples, wine, and gentle decay, what D. H. Lawrence described as an “exquisite odour of leave-taking.”

Loquat Loquats bear little resemblance to their cousin pomes. They are small, elongated fruits of a Chinese tree, Eriobotrya japonica, which was greatly improved by the Japanese and taken to many subtropical regions in the 19th century, notably Sicily, where they are called nespole. They usually ripen early, before cherries. They have a mild, delicate flavor and a wall of carotenoid-containing flesh that runs from white to orange, surrounding several large seeds. U.S. varieties are mainly ornamental and produce small fruit, while European and Asian fruits may approach a half pound/250 gm. They’re eaten fresh, made into jellies and jams, and cooked in a spicy syrup in the manner of “pickled” peaches. Loquats are neither climacteric nor chill-sensitive, and so keep well.

Stone Fruits: Apricot, Cherry,
Peach, and Plum

Stone fruits are all species of the genus Prunus, members of the large rose family and relatives of the pome fruits. They owe their name to the stone-hard “shell” that surrounds a single large seed at their center. Though the 15 species of Prunus are found throughout the northern hemisphere, the important stone fruits mostly come from Asia. They do not store starch and so get no sweeter after harvest, though they do soften and develop aroma. Their internal tissues tend to become mealy or break down in prolonged cold storage, so fresh stone fruits are more seasonal than hardier apples and pears. Like some of the pome fruits, stone fruits accumulate the indigestible sugar alcohol sorbitol (a frequent ingredient in sugar-free gums and candies, p. 662); they’re also rich in antioxidant phenolic compounds. The seeds of stone fruits are protected by a cyanide-generating enzyme that also produces the characteristic aroma of almond extract (almonds are seeds of

Prunus amygdalus). They thus lend an almond character when included in sugar and alcohol preserves, and can replace “bitter almonds” in European pastries and sweets (p. 506).

Apricot The apricots that are most familiar in the West are fruits of Prunus armeniaca, a native of China that was taken to the Mediterranean during Roman times. There are now thousands of different varieties, white and red (from lycopene) as well as orange, and most of them adapted to specific climates; apricots flower and fruit early (the name comes from the Latin praecox, “precocious”), and therefore bear best in areas with mild, predictable winters. Several other species are grown in Asia, including P. mume, whose fruits the Japanese salt-pickle and color red to make the condiment umeboshi. The distinctive aroma of fresh apricots comes from a rich mixture of terpenes that provide citrus, herbal, and floral notes, and from peach-like compounds (lactones). They are rich in pectin, which gives them a luscious texture when fully ripe, a meaty texture when dried.

Stone fruits and the flower from which they arise. Peaches and cherries derive from an ovary that sits above the base of the flower parts, so the fruits show no remnants of the flower.

Apricots are delicate fruits that don’t travel well, so most are processed. They’re especially suited to drying, which concentrates their sweet-tart flavor well even when they’re overripe. Most dried apricots in the United States come either from a few western states or from Turkey, which exports a relatively pale, bland variety with half the carotenoid pigments and acidity of the Blenheim and Patterson varieties of California. The fruits are dried in the sun in early summer for one or two weeks, until they reach a moisture content of 15–20%. Usually they’re treated with sulfur dioxide to preserve the abundant beta-carotene and other carotenoids, vitamin C, and fresh flavor. Unsulfured apricots are brown and have a flatter, cooked taste.

Cherry Cherries come in two basic types from two different species, both of which are native to western Asia and southeast Europe. Sweet cherries are the fruits of Prunus avium, which is probably one of the parents of the sour cherry, Prunus cerasus. Sweet and sour cherries differ mainly in their maximum sugar content, with sweet cherries accumulating significantly more. Cherries don’t improve once they’re harvested, so they must be picked ripe and fragile. Most sweet cherries grown in the United States are sold fresh, but far more sour cherries are grown, and most of these are processed. Cherries are prized not only for their flavor, but for their color, which may range from very deep red (rich in anthocyanins) to a pale yellow. The red varieties are an excellent source of phenolic antioxidants.

Cherry flavor comes mainly from almondy benzaldehyde, a flowery terpene (linalool), and essence of clove (eugenol). Heating increases both the almond and flowery notes, especially if the pits are left in the fruit. This is why the classic French cherry clafoutis, a custardy tart, is intensely flavored but requires care in eating!

The familiar “maraschino” cherry originated several centuries ago in northeastern Italy and the neighboring Balkans, where the local marasca cherry was preserved in its own liqueur for winter eating. In the modern industrial version, light-fleshed varieties are bleached with sulfur dioxide and stored in brine until needed, then infused with sugar syrup, dyed cherry red, flavored with almond extract, and pasteurized. After all that, what’s left of the original cherry is mainly its skeleton, the cell walls and skin.

Peach and Nectarine Peaches and nectarines are both fruits of the species Prunus persica. Nectarines are varieties with a smooth skin that are usually also smaller, firmer, and more aromatic than their fuzzy siblings. The words “peach” and “persica” come from “Persia,” by way of which the fruit reached the Mediterranean world from China by about 300 BCE.

Modern peach and nectarine varieties fall into a handful of categories. Their flesh may be white or yellow, and either firm or melting, strongly attached to the large central stone (clingstone) or easily detached (freestone). The genetically dominant characteristics are white, melting, freestone flesh. Yellow varieties were developed mainly after 1850, and firm clingstone varieties have been bred mainly for drying, canning, and improved tolerance of shipping and handling. The yellow coloration comes from a handful of carotenoid pigments, beta-carotene among them; rarer red varieties contain anthocyanins (as the skin often does). Peaches begin to ripen at the stem end and along the groove, or “suture,” and are said to continue their flavor development even after harvest. The distinctively aromatic flavor of peaches and nectarines comes largely from compounds called lactones, which are also responsible for the aroma of coconut; some varieties also contain clove-like eugenol.

The most frequent problem with peaches is mealy flesh, apparently due to impaired pectin breakdown when the fruit has been temporarily stored in the cold, at temperatures below about 45ºF/8ºC. This is especially common in supermarket fruits.

Plum and Plum Hybrids Most plums are the fruits of two species of Prunus. A Eurasian species, P. domestica, gave rise to the European plums, which include French and Italian prune plums, the greengage and Reine Claude, the yellow-egg and imperatrice. The most common of these are the prune types, purplish-blue ovals with a meaty, semimelting, semifreestone flesh. The second, Asian species, P. salicina, originated in China, was improved in Japan, and further bred by Luther Burbank and others in the United States after 1875. Varieties of the Asian species (Santa Rosa, elephant heart, and many others) tend to be larger, rounder, from yellow to red to purple, clingstone, and often melting. European plums are usually dried or made into preserves, Asian plums eaten fresh. Plums are climacteric fruit, so they can be harvested before ripening, stored at 32ºF/0ºC for up to 10 days, and then allowed to mature slowly at 55ºF/13ºC. Their aroma varies from kind to kind, but generally includes almondy benzaldehyde, flowery linalool, peachy lactones, and spicy methyl cinnamate.

Plum-apricot hybrids, known as pluots (more plum parentage) or plumcots (equal parentage), are generally sweeter than plums and more complex in aroma. There are also a number of minor plums, among them the English damson and sloe (P. insititia and spinosa), the latter small, astringent fruits that are steeped to make sloe gin.

Prunes The firm-fleshed prune plums dry well in the sun or during 18–24 hours in a dehydrator at around 175ºF/79ºC. They develop a rich flavor thanks to the concentration of sugars and acids — nearly 50% and 5% of their weight respectively — and to browning reactions that generate caramel and roasted notes as well as their color, a brown-black deep enough to be attractive rather than drab. This richness is the reason that prunes work well in many savory meat dishes. Prunes are such a concentrated source of antioxidant phenolic compounds (up to 150 mg per 100 gm) that they make an excellent natural flavor stabilizer: they prevent the development of warmed-over flavor in ground meats when included at the rate of just a few percent (1 tablespoon per pound). They’re also rich in moisture-retaining fiber and sorbitol and so are used to replace fat in hamburgers and a variety of baked foods. (Dried cherries have many similar properties and uses.) Their well-known laxative action on the human digestive tract is not entirely understood but probably involves the sugar alcohol sorbitol (p. 662), which accounts for up to 15% of the weight of both prune and juice. We can’t digest sorbitol, so it passes into our intestines where it may have a number of stimulating effects.

Common berries. Blueberries (left) are true berries, or single fruits derived from the plant’s ovaries. Caneberries and strawberries are not true berries, but multiple fruits that develop from many ovaries set in the same flower receptacle. Each little segment of a raspberry or blackberry (center) is a complete stone fruit. The strawberry (right) is a “false fruit”: the small “seeds” borne on the surface of the swollen flower base are dry but entire fruits that correspond to the caneberry segments.

Berries, Including Grapes
and Kiwi Fruit

Though the term berry has a precise botanical definition, in common usage it generally refers to small fruits borne on bushes and low plants, not trees. Most of our familiar berries are natives of northern woodlands.

Caneberries: Blackberries, Raspberries, and Relatives Caneberries are fruits of the genus Rubus, which grows naturally across most of the temperate northern hemisphere in the form of long thin, thorny stalks, or canes. There are hundreds of species of blackberry native to both Europe and the Americas, but just a few species of raspberry. Serious caneberry cultivation probably began around 1500, and a number of blackberry-raspberry hybrids have been created, including boysenberry, loganberry, youngberry, and tayberry from American species, the Bedford giant from European species. Less familiar caneberries include cloudberries, a yellow-orange Scandinavian fruit, and dark red, intensely aromatic Arctic bramble fruits.

Caneberries are composite fruits: a single flower has from 50 to 150 ovaries, and each ovary makes a separate small fruitlet, like a miniature plum with a stony seed. The fruitlets are nourished through contact with the flower base and held together by the entanglement of small hairs borne on their surface (the original inspiration for Velcro). When they ripen, blackberries separate from the cane at the bottom of the flower base, so the base comes with the fruit; raspberries instead separate from the base itself, and so have an inner cavity. Caneberries are climacteric fruit, and have one of the highest respiration rates of any fruit; thanks to this and their thin skin, they’re extremely fragile and perishable.

Raspberries have a distinctive flavor due to a compound dubbed the raspberry ketone, and also have a violet-like note (from carotenoid fragments called ionones). The flavor of wild berries has been found to be by far the most intense. Blackberries vary in their flavor, the European varieties relatively mild, the American more intense, with spicy aroma notes (from terpenes). Most caneberry colors are provided by anthocyanin pigments, whose sensitivity to pH can cause dark purple blackberries to turn red when frozen (p. 281). These fruits are a good source of phenolic antioxidants, at least one of which (ellagic acid) actually increases during jam making. When made into preserves, the numerous caneberry seeds (several thousand per quarter pound/100 gm) can sometimes absorb syrup, become translucent, and give the normally deep-colored jam a milky dullness.

Blueberry, Cranberry, and Relatives These berries are borne by several different species in the genus Vaccinium, which ranges across northern Europe and North America.

Blueberry Blueberries are the small fruits of a bushy North American species of the genus Vaccinium, which ranges from the tropics to the arctic. V. angustifolium and corymbosum are weedy pioneers in burned fields, and their fruits were gathered from the wild until the 1920s, when the first selected “highbush” (corymbosum) plants were developed in New Jersey. The bilberry, V. myrtillus, is a European relative, and the rabbit-eye blueberry, V. ashei, a similar but less flavorful native of the southern United States. The huckleberry, various species of Vaccinium, has a few large hard seeds, while blueberries have many small ones.

Blueberries have a distinctive, spicy aroma apparently due to several terpenes, and are rich in phenolic antioxidants and in anthocyanin pigments, especially in the skin. These small berries freeze well, and retain their shape and substance when baked. The pigments can turn odd shades of green if cooked with alkaline ingredients (for example, baking soda in muffins).

Cranberry and Relatives Cranberries are fruits of the North American perennial vine Vaccinium macrocarpon, which is native to low, swampy areas of northern states from New England to the Midwest. Cultivation and efforts at improvement began in the 19th century, and the familiar jelly-like cranberry sauce was born early in the 20th century when a large producer decided to process his damaged berries into a canned puree.

Cranberries can be harvested dry, with a comb-like machine, or wet, by flooding the bog. Dry-harvested berries keep better, for several months. Cranberries store well for a couple of reasons. One is their high acidity, exceeded only by lemons and limes, and the main obstacle to eating them straight. The other is their very high content of phenolic compounds (up to 200 milligrams per 100 grams), some of which are antimicrobial and probably protect the fruit in its damp habitat. Many of these phenolic materials are also useful to us, some as antioxidants and others as antimicrobials. One example is benzoic acid, now a common preservative in prepared foods. A particular pigment precursor in cranberries (also found in blueberries) prevents bacteria from adhering to various tissues in the human body, and so helps prevent urinary tract infections.

The spicy aroma of cranberries is created by a combination of terpenes and spicy phenolic derivatives (cinnamates, benzoates, vanillin, almondy benzaldehyde). Some of its phenolic compounds contribute a notable astringency. Cranberries are rich in pectin, which is why a barely cooked puree thickens immediately into a sauce; it’s also why cranberries macerated in alcohol may cause the alcohol to gel.

Lingonberries or cowberries are the fruit of a European relative of the cranberry, V. vitis-idaea; they have a distinctive, complex flavor. The European cranberry, V. oxycoccus, has a stronger and more grassy, herbaceous flavor than the American species.

Currants and Gooseberries Currants and gooseberries are all species of the genus Ribes, which is found in northern Europe and North America. These small berries don’t appear to have been cultivated until around 1500. (Their cultivation in the United States has been retarded by federal and state restrictions because they can harbor a disease that attacks white pines.) There are white and red currants, R. sativum and R. rubrum, and hybrids between the two. The black currant R. nigrum, is higher in acid than the others, and has a distinctively intense aroma made up of many spicy terpenes, fruity esters, and a musky, “catty” sulfur compound that is also found in sauvignon blanc wines. Black currants are also notably rich in vitamin C and in antioxidant phenolic compounds — as much as 1% of their weight — about a third of which are anthocyanin pigments. Currants are mainly made into preserves, and the French make black currants into a liqueur, crème de cassis.

The gooseberry, R. grossularia, is larger than the currant, and is often picked unripe for cooking in tarts and sauces. The jostaberry is a black currant–gooseberry cross.

Grapes Grapes are the berries of woody vines in the genus Vitis. V. vinifera, the major source of wine and table grapes, is native to Eurasia (p. 772). There are also about 10 grape species native to temperate Asia, and 25 to North America, including the V. labrusca that gives us Concord and Catawba grapes. About two-thirds of the world’s grape production goes to make wine; of the rest, about two-thirds are eaten fresh and a third are made into raisins. There are many thousands of grape varieties. Most wine varieties originated in Europe, while varieties for eating fresh or making into raisins can often be traced back to western Asian parents. Wine grapes come in relatively small clusters and are acidic enough to help control the yeast fermentation; table grapes come in large clusters and are less tart; raisin varieties have a thin skin, high sugar content, and loose cluster structure to facilitate drying. The commonest table and raisin grape in the United States, the Thompson seedless or sultana, is a variant of an ancient Middle Eastern all-purpose variety, the Kishmish. Table grapes are quite diverse. They may be seedy or seedless, deep purple with anthocyanins or pale yellow; their sugar content may range from 14 to 25%, their acidity from 0.4 to 1.2%. They may have a fairly neutral, green aroma (Thompson seedless), or be flowery and citrusy from terpenes (muscat), or musky with anthranilate and other esters (Concord and other American varieties). Most commercial varieties today have been bred to be seedless, crisp, tart, and sweet, with a long storage life. Thompson seedless grapes picked in the cool of the morning and treated with antimicrobial sulfur dioxide can be held for as long as two months at 32ºF/0ºC.

Raisins Grapes are easily preserved by sundrying to make raisins. In the United States this is usually done by laying the grapes on paper between rows in the vineyard for about three weeks. Raisins are naturally brown and have caramel flavor notes due to a combination of browning-enzyme oxidation of phenolic compounds and direct browning reactions between sugars and amino acids (pp. 269, 778). Both of these processes are accelerated by high temperatures, so a lighter color can be obtained by drying the grapes in the shade. Golden raisins are made by treating the grapes with antioxidant sulfur dioxide and drying them mechanically at controlled temperatures and humidities; the result is a much fruitier, lighter flavor. Zante “currants” are made from the small black Corinth grape, and are tarter than ordinary raisins thanks to their higher proportion of skin to pulp.

Verjus and Saba Two ancient grape preparations make versatile ingredients in the kitchen. Fruits thinned six to eight weeks before the main harvest are crushed and filtered to produce verjus, a tart alternative to vinegar or lemon juice, slightly sweet, with a delicate green aroma. And ripe grapes are cooked down to a thick, sweet-tart, aromatic syrup (Roman sapa, Italian saba or mosto cotto, Turkish pekmez, Arab dibs). Like syrups from other fruit (pomegranates), grape syrup was an important sweetener in the times before cheap table sugar, but provides tartness and aroma as well as sweetness. It’s thought that balsamic vinegar may have evolved from grape syrup that was kept long enough to ferment (p. 775).

Kiwi “Kiwi” fruit is the name that New Zealand producers came up with for the striking, tart berry of a Chinese vine, Actinidia deliciosa, when they pioneered its international marketing in the 1970s. Several other species of Actinidia are now also cultivated, including the yellow-to-red-fleshed A. chinensis. Kiwi fruit are unusual in appearance and ripening behavior. Their thin, hairy skin doesn’t change color during ripening, and the translucent inner flesh is green with chlorophyll, with as many as 1,500 small black seeds embedded in a ring and connected to the core by white rays of vascular tissue. (There are also chlorophyll-free varieties with yellow, red, and purple flesh.) Cross-sectional slices of kiwi are thus very attractive. When harvested, kiwi fruits contain a large amount of starch. During months of storage at 32ºF/0ºC, the starch is slowly converted to sweet sugars. Then at room temperature they undergo a climacteric ripening that takes about 10 days. The flesh softens and the aroma becomes more pronounced, with strongly fruity esters (benzoates, butanoates) coming to dominate more delicate, grassy alcohols and aldehydes. Some kiwi varieties are rich in vitamin C and in carotenoids.

Kiwi fruits present a couple of challenges to the cook. They contain a strong protein-digesting enzyme, actinidin, which can damage other ingredients in a mixture and irritate sensitive skin. Heat inactivates enzymes, but it also muddies the fruit’s delicate color and translucency. Kiwi fruits also contain crystals of calcium oxalate (p. 259), which pureeing, juicing, and drying can make more apparent and irritating in the mouth and throat.

Mulberry Mulberries are the surprisingly small, fragile, composite fruits of trees of the genus Morus. They resemble the blackberry, but each small fruitlet actually arises from a separate flower on a short flowering stalk. The white mulberry, M. alba, is native to China, where its leaves have long been used to feed silkworms. Its color ranges from white to purple, and it is relatively bland; often it’s dried, which helps intensify its flavor. The Persian or black species, M. nigra, comes from west Asia; it’s always a dark purple and is more flavorful. The North American red mulberry, M. rubra, is mainly tart. Mulberries are used to make preserves, syrups, and sorbets.

Strawberry Strawberries come from small perennial plants of the genus Fragaria, whose 20 species range across the northern hemisphere. The plants are easy to grow and therefore are grown widely, from sub-arctic Finland to tropical Ecuador. The strawberry is unusual in bearing its “seeds” on the surface of the fleshy portion, not inside. The “seeds” are actually miniature dry fruits (achenes), similar to buckwheat and sunflower “seeds,” and the fleshy portion is the flower’s swollen base, not its ovary. During ripening, the cells of the strawberry interior enlarge and pull apart from each other. The berry is therefore filled with tiny air pockets, and its shape is maintained by the pressure of the cell contents pushing each cell onto its neighbors. When this pressure is released, by water loss from drying out or from freezing that punctures the cell walls, the structure weakens and the fruit becomes soft and mushy. Strawberries don’t improve once picked, so they must be picked ripe. Thanks to their thin skin and fragile structure, they only last a few days, even in cold storage.

The pineapple note in standard strawberries comes from the presence of ethyl esters. Some sulfur compounds and a complex caramel-like oxygen-containing ring, furaneol (also characteristic of pineapple), round out strawberry aroma. The smaller European woodland strawberries have a flavor of Concord grapes thanks to anthranilates, and a clove-like spicy note (from the phenolic eugenol). Strawberries are rich in ascorbic acid and in phenolic antioxidants, including its red anthocyanin pigments. They are poor in pectic materials, so strawberry preserves are often supplemented with prepared pectin or pectin-rich fruits.

The Domestication of the Strawberry Most of the strawberries grown today derive from two American species which were brought together and hybridized less than 300 years ago — and in Europe, not in the Americas!

Europe had its own native strawberry (F. vesca and F. moschata), which is now called the “wild” strawberry or fraise de bois(“woodland strawberry”), even though it’s cultivated. This strawberry was mentioned in Roman literature, subsequently cultivated, and by the 15th century had a wonderful fragrance but was still small, pithy and unproductive. Early European visitors to North America were impressed by the size and vigor of an American species, F. virginiana, and brought it back to Europe. Then a Frenchman by the stunningly appropriate name of Frézier found the walnutsized fruits of another New World species, F. chiloensis, growing in Chile, and took that species to France in 1712. Around 1750, in the strawberry-producing area around Plougastel in Britanny, an accidental hybrid between the two American species arose. Then across the Channel in England, a natural mutant of the Chilean species arose, large and pink, with a shape and aroma reminiscent of pineapple. Modern strawberry varieties, large and red and flavorful, derive from these two all-American ancestors. They have been given the scientific name F. x ananassa to indicate their hybrid origins (x) and distinctive pineapple aroma (ananassa).

Elderberry and Barberry Elderberries and barberries are minor fruits worth rediscovering. Elderberries are pleasantly aromatic fruits borne by trees of the genus Sambucus, which are found across the northern hemisphere. They’re usually cooked or made into wine because they are too tart to be enjoyed raw, and contain antinutritional lectins (p. 259) that require heating to be inactivated. Elderberries are rich in anthocyanin pigments and antioxidant phenolic compounds. So is the barberry, from shrubby species of the northern-hemisphere Berberis, which is something like a miniature cranberry and dries well. Barberries are much used in Persian cooking, where they provide the tart rubies in a dish called jeweled rice.

Other Temperate Fruits

Ground Cherry This is one name for a couple of related fruits from low-lying plants in the nightshade family, close relatives of the tomatillo (p. 331). The Peruvian or Cape ground cherry or gooseberry, Physalis peruviana, came from South America, while the ordinary ground cherry, P. pubescens, is native to both North and South America. Both fruits resemble miniature, thick-skinned yellowish tomatoes, are enclosed in papery husks (thus another name, husk tomato), and keep well at room temperature. The Peruvian ground cherry has floral and caramel aroma notes in addition to generically fruity esters. These fruits are made into preserves and pies.

Persimmon Persimmons are fruits of trees in the genus Diospyros, which is native to both Asia and North America. There’s a plum-sized native American persimmon, D. virginiana, and a Mexican species known as the black sapote (D. digyna), but the most important persimmon species worldwide is D. kaki, a tree with applesized fruits native to China and adopted by Japan; it’s sometimes said that persimmons are to the Japanese what apples are to Americans. Japanese persimmons are sweet, low-acid, mild fruits, with a few brown seeds surrounded by flesh that’s bright orange from various carotenoid pigments, including beta-carotene and lycopene. They have a very mild aroma reminiscent of winter squash that probably derives from breakdown products of carotenoids.

Japanese persimmons come in two general kinds, astringent and nonastringent. Astringent varieties, including the tapered Hachiya, have such high levels of tannins that they’re edible only when completely ripe, with translucent and almost liquid flesh. Nonastringent types, including the flat-bottomed Fuyu or Jiro, are not tannic, and can be eaten while underripe and crisp (they also don’t get as soft as the astringent types). Centuries ago, the Chinese figured out a way to remove the astringency from unripe persimmons before they ripen. This method may be the first example of controlled-atmosphere storage! They simply buried the fruit in mud for several days. It turns out that when the fruits are deprived of oxygen, they shift their metabolism in a way that results in the accumulation of an alcohol derivative called acetaldehyde, and this substance binds with tannins in the cells, thus preempting them from binding to our tongues. Modern cooks can accomplish the same thing by wrapping persimmons snugly in a truly airtight plastic film, polyvinylidene chloride (saran).

Persimmons are commonly eaten raw, frozen whole into a natural sorbet, and made into pudding. Traditional American persimmon pudding owes its distinctive black-brown color to the combination of the fruit’s glucose and fructose, flour and egg proteins, alkaline baking soda, and hours of cooking, which encourage extensive browning reactions (p. 778; replace the baking soda with neutral baking powder or shorten the cooking time and you get a light orange pudding). Persimmon flesh can be whipped into a long-lived foam thanks to its tannins, which help bind fragments of cell walls together to stabilize the air pockets. In Japan, most Hachiya persimmons are dried, massaged every few days to even out the moisture and break down some of the fibrousness to a soft, doughy consistency.

Rhubarb Rhubarb is a vegetable that often masquerades as a fruit. It is the startlingly sour leaf stalks of a large herb, Rheum rhabarbarum, that is native to temperate Eurasia and became popular in early 19th-century England as one of the first fruit-like produce items to appear in the early spring. The rhubarb root had long been used as a cathartic in Chinese medicine, and traded widely as a medicinal. The stalks were also used as a vegetable in Iran and Afghanistan (in stews, with spinach) and in Poland (with potatoes). By the 18th century the English were using them to make sweet pies and tarts. The 19th century brought better varieties and techniques for digging up mature roots and forcing rapid stalk growth in warm dark sheds, which produced sweeter, tenderer stalks. These improvements, cheaper sugar, and a growing supply resulted in a rhubarb boom, which peaked between the world wars.

Rhubarb stalks may be red with anthocyanin pigments, green, or an intermediate shade, depending on the variety and production techniques. Their acidity is due to a number of organic acids, notably oxalic acid, which contributes about a tenth of the total acidity of 2–2.5%. (This is double or triple the oxalate content of spinach and beets.) Rhubarb leaves are said to be toxic in part due to their high oxalate content, as much as 1% of the leaf weight, but other chemicals are probably also responsible. Today rhubarb is available much of the year thanks to greenhouse production, though some cooks prefer the more intense flavor and color of the field-grown crop of late spring. The color of red stalks is best preserved by minimizing both the cooking time and the quantity of added liquid, which dilutes the pigments.

Fruits From Warm
Climates: Melons, Citrus
Fruits, Tropical Fruits,
and Others

Melons

Except for the watermelon, melons are fruits of Cucumis melo, a close relative of the cucumber (C. sativus) and a native of the semiarid subtropics of Asia. The melon plant was domesticated in central Asia or India and arrived in the Mediterranean at the beginning of the 1st century CE, where their large size and rapid growth made them a common symbol of fertility, abundance, and luxury. There are many melon varieties with distinctive rinds, flesh colors (orange types are an excellent source of beta-carotene), textures, aromas, sizes, and keeping qualities.

Melons are generally used fresh, either sliced or pureed. They contain a protein-digesting enzyme, cucumisin, and thus will prevent gelatin gels from setting unless the enzyme is denatured by cooking or an excess of gelatin is used. The melon surface can become contaminated with microbes in the field and cause food poisoning when the microbes are introduced into the flesh during cutting; it’s now recommended that melons be thoroughly washed in hot soapy water before preparing them.

Melon Families and Qualities The most common Western melons fall into two families:

• Summer melons are highly aromatic and perishable, and usually have rough rinds. They include true cantaloupes and muskmelons.
• Winter melons are less aromatic and less perishable, and usually have smooth or wrinkled rinds. They include honeydews, casabas, and canaries.

The differences between the two melon families are caused by differences in their physiology. The aromatic summer melons are generally climacteric fruits that (with the exception of cantaloupes) separate from their stems when ripe; and they contain active enzymes that generate more than 200 different esters from amino acid precursors, and thus help create their characteristically rich aroma. The winter melons are generally nonclimacteric fruit like their relatives the cucumbers and squashes, and have low ester-enzyme activities and therefore a milder flavor.

Vine-ripening is important for all melons because they don’t store starch and so get no sweeter after harvest. A remnant of the stem on an aromatic melon indicates that it was harvested before becoming fully ripe, while all winter melons (and true cantaloupes), even ripe ones, carry a piece of stem. The aroma of melons may continue to develop off the vine, but will not be the same as the aroma of vine-ripenedfruit. In addition to fruity esters, melons contain some of the same green, grassy compounds that give cucumbers their distinctive flavor, as well as sulfur compounds that provide a deeper, more savory dimension.

Minor Melons In addition to the Western melons, there are several groups of Asian melons, including Japanese pickling or tea melons, many of them crisp-fleshed, and the flexuosus group, long and twisted like a snake, which includes the “Armenian cucumber.” There is also the dudaim group of small, especially musky melons used in the U.S. South and elsewhere for preserves and simply to scent the air (pocket melon, pomegranate melon, smell melon); dudaim is Hebrew for “love-plants.” The horned melon, also called jelly melon and kiwano, is the fruit of Cucumis metuliferus, a native of Africa with a spiky yellow skin and a relatively scant amount of emerald-green, translucent gel surrounding its seeds. The gel has a sweet cucumbery flavor and is used in drinks, fresh sauces, and sorbets. The hollowed-out skin makes a decorative container.

Watermelon The watermelon is a distant relative of the other melons, the fruit of an African vine, Citrullus lanatus, whose wild relatives are very bitter. The Egyptians were eating it 5,000 years ago, and the Greeks knew it by the 4th century BCE. World production of watermelons is now double the production of all other melons combined. Watermelons are notable for the large size both of their cells, which are easily seen with the naked eye, and their fruits, which can reach 60 lb/30 kg and more. Unlike other melons, the watermelon consists of seed-bearing placental tissue rather than seed-surrounding — thus seed-free — ovary wall. “Seedless melons,” which actually contain small undeveloped seeds, were first bred in Japan in the 1930s. The classic watermelon is dark red with the carotenoid pigment lycopene, and in fact is a much richer source of this antioxidant than tomatoes! Recent years have brought yellow-orange varieties. A good watermelon has a crunchy, crisp, yet tender consistency, a moderately sweet taste, and a delicate, almost green aroma. External signs of quality are a substantial heaviness for the melon’s size, yellow skin under-tones indicative of chlorophyll loss and thus ripeness, and a solid resonance when thumped.

In addition to being eaten fresh, watermelon flesh is pickled and candied (often after a preliminary drying), and cooked down into a syrup or thick puree. The dense rind is often made into sour or sweet preserves. There is a subgroup of watermelons, C. lanatus citroides, known as citron or preserving melons, with inedible flesh but abundant rind for these preparations. Both melon and watermelon seeds are used in several regions, roasted or ground and infused to make beverages.

Fruits From Arid Climates:
Fig, Date, and Others

Cactus Pear “Cactus pear” is the modern marketing term for “prickly pear” (Spanish tuna), the fruit of the American cactus Opuntia ficus-indica. The species name comes from the early European idea that the dried fruit was an “Indian fig.” The cactus arrived in the Old World in the 16th century and spread like a weed in the southern Mediterranean and Middle East. While both stem pads and fruits are eaten in the Americas, Europeans concentrated on the fruits, which ripen in the summer and fall and have a thick skin, green to red or purple, and many hard seeds embedded in a reddish, sometimes magenta flesh. The main pigment is not an anthocyanin but a beet-like betain (p. 268). The aroma is mild, reminiscent of melons thanks to similar alcohols and aldehydes. Like the pineapple and kiwi, cactus pears contain a protein-digesting enzyme that can affect gelatin gels unless it’s inactivated by cooking. The pulp is removed and generally eaten fresh as juice or in salsas, or boiled down to a syrup or further to a pasty consistency. The paste is made into candies and cakes with flour and nuts.

Dates Dates are the sweet, easily dried fruits of a desert palm, Phoenix dactylifera, that can tolerate some cold and thrives as long as it has a source of water. Their original home was Middle Eastern and African oases, where they were being cultivated with artificial irrigation and pollination more than 5,000 years ago; they’re now also grown in Asia and California. Though we usually see only two or three dried versions, there are thousands of different date varieties that differ in size, shape, color, flavor, and ripening schedule.

Growers and aficionados distinguish four stages in date development: green and immature; mature but unripe, when they’re yellow or red and hard, crunchy, and astringent; ripe (Arabic rhutab), when they’re soft, golden brown, and delicate; and finally dried, when they’re brown and wrinkled and powerfully sweet. Drying is usually done on the tree. Dates are moist and succulent when fresh, from 50 to 90% water, and chewy and concentrated when dry, with less than 20% moisture. Dry dates are 60 to 80% sugar, together with some texture-providing pectins and other cell-wall materials, and a few percent fatty materials, including the surface wax. They’re ground into a coarse powder to make “date sugar.”

The drying process causes dates to develop a brown color and browned flavor thanks both to the action of browning enzymes on phenolic materials, and to the browning reactions between concentrated sugars and amino acids. Some varieties rich in phenolic materials, notably the Deglet Noor, can develop an increased astringency and red coloration when heated. Phenolic and other compounds give dates notable antioxidant and antimutagenic activities.

Fig Figs are the fruits of Ficus carica, a tree native to the Mediterranean and Middle East, and a relative of the mulberry. Because like the date they readily dry in the sun to a long-keeping, concentrated source of nourishment, they have been an important human food for many thousands of years. The fig is the fruit mentioned most often in the Bible, and was said to grow in the Garden of Eden. Spanish explorers brought it to the Americas via Mexico, and it now grows in many dry subtropical regions. There are many varieties, some green-skinned and some purple, some with bright red interiors. Ripe fresh figs are 80% water, very fragile and perishable. The vast bulk of the world crop is preserved by drying, a process that normally begins on the tree and then concludes on the orchard floor or in mechanical dryers.

The fig is unusual in being more flower than fruit. The main body is a fleshy flower base folded in on itself, with an open pore opposite the stem, and inner female florets that develop into small, individual dry fruits that crunch like “seeds.” The florets are pollinated by tiny wasps that enter through the pore. Many fig varieties will set fruit without pollination and produce “seeds” with no embryo inside, but fig experts say that fertilization and seed development seem to generate different flavors. (Wasps carry microbes into the fig interior, so fertilized fruits also suffer greater spoilage.) Smyrna figs and their descendants (“Calimyrna” is the California version) will not set fruit unless fertilized. They must be grown alongside a separate and inedible crop of “caprifigs,” from which the wasps obtain fig pollen and lay their eggs.

The walls of the fig fruit contain latex vessels that carry a protein-digesting enzyme, ficin, and tannin cells that contribute astringency. Figs are remarkable for containing very large amounts of phenolic compounds, some of them antioxidants, and large amounts of calcium for a fruit. When ripe, figs have a unique aroma that comes mainly from spicy phenolic compounds and a flowery terpene (linalool).

Jujube Jujubes, also known as Chinese dates, are the fruits of Ziziphus jujuba, a tree native to central Asia. They do bear some resemblance to dates, as do the version known in India as the ber (Z. mauritania). Both trees tolerate heat and drought and are now grown in arid regions throughout the world. Jujubes are small, somewhat dry and spongy, more sweet than tart. They’re an excellent source of vitamin C, containing more than double the amount in an equal weight of oranges. They’re eaten fresh, dried, pickled, in rice-based cakes, and fermented into alcoholic drinks.

Pomegranate Pomegranates are fruits of the shrubby tree Punica granatum, a native of the arid and semiarid regions of the Mediterranean and western Asia; the finest varieties are said to grow in Iran. With their dull, dry rind surrounding two layered chambers of translucent, ruby-like fruitlets (there are also pale and yellow varieties), they figured very early in mythology and art. Pomegranate-shaped goblets have been found in prehistoric Troy, and in Greek myth it was a pomegranate that tempted Persephone and kept her in the underworld. Pomegranates are very sweet, fairly tart, and often astringent thanks to their strongly pigmented juice well-stuffed with anthocyanins and related phenolic antioxidants. Juice manufactured by crushing whole fruits is much more tannic than the fruitlets themselves; the rind is so rich in tannins that it was once used for tanning leather! Because each fruitlet contains a prominent seed, pomegranates are usually processed into juice, which then can be used as is or cooked down to make a syrup or “molasses,” or fermented into a wine. True grenadine is pomegranate juice mixed with a hot sugar syrup. Today most commercial grenadines are synthetic. In northern India, pomegranate fruitlets are dried and ground for use as an acidifying powder.

The Citrus Family: Orange,
Lemon, Grapefruit, and Relatives

Citrus fruits are among the most important of all tree fruits. From their birthplace insouthern China, northern India, and Southeast Asia they spread throughout the subtropics and mild temperate zones of the world. Ancient trade took the citron to western Asia and the Middle East before 500 BCE, and medieval crusaders brought sour oranges back with them to Europe; Genoese and Portuguese traders introduced sweet oranges around 1500, and Spanish explorers carried them to the Americas. Today, Brazil and the United States produce most of the world’s oranges. Barely a century ago, oranges were special holiday treats; now much of the Western world starts its day with orange juice.

The fig. It contains small flowers within the fleshy “fruit,” which is actually the swollen flower base. The fig is an inverted version of the strawberry: it surrounds rather than underlies the true tiny fruits, or achenes.

Why are citrus fruits so popular? They offer an unusual set of virtues. Above all, their peels have distinctive and strong aromas, and these may have been their original attraction, well before human selection developed varieties with sweet juices. The improved varieties do have a refreshing, tart to sweet-tart juice that can be extracted with little pulp. The peel is rich in gel-making pectins. And citrus fruits are also fairly robust. They’re nonclimacteric, so they retain their quality for some time after harvest, and the meaty peel offers good protection against physical damage and attack by spoilage microbes.

Citrus Anatomy Each segment of a citrus fruit is a compartment of the ovary, and is stuffed with small, elongated bags called vesicles, each of which contains many individual microscopic juice cells that fill with water and dissolved substances as the fruit develops. Surrounding the segments is a thick, white, spongy layer called the albedo, usually rich in both bitter substances and in pectin. And riding atop the albedo is the skin, a thin, pigmented layer with tiny spherical glands that create and store volatile oils. Flexing a piece of citrus peel will burst the oil glands and send a visible, aromatic — and flammable! — spray into the air.

Citrus Color and Flavor Citrus fruits owe their yellow and orange colors (orange comes ultimately from the Sanskrit word for the fruit) to a complex mixture of carotenoids, only a small portion of which has vitamin A activity. The fruit peels start out green, and in the tropics often stay that way even when the fruit ripens. In other regions, cold temperatures trigger destruction of chlorophyll in the peel, and the carotenoids become visible. Fruits of commerce are often picked green and treated with ethylene to improve their color, and coated with an edible wax to slow moisture loss. Pink and red grapefruit are colored by lycopene, and red sweet oranges by a mixture of lycopene and beta-carotene and by cryptoxanthin. The purple-red of blood oranges comes from anthocyanins.

Citrus anatomy. The protective outer rind includes aromatic oil glands embedded in a bitter white pith, the albedo. Each segment, or carpel, of a citrus fruit consists of many delicate juice sacs contained within a strong membrane.

The taste of citrus fruits is created by a handful of substances, including citric acid (so named because it is typical of the family), sugars, and certain bitter phenolic compounds, which are usually concentrated in the albedo and peel. Citrus fruits are surprisingly rich in the savory amino acid glutamate, sometimes rivaling the tomato (oranges reach 70 milligrams per 100 grams, grapefruits 250). They contain little starch and therefore don’t sweeten much after picking. Usually the blossom end of the fruit contains both more acid and more sugars, and so has a more intense taste than the stem end. Neighboring segments can also vary significantly in taste.

Citrus aroma is produced both by the oil glands in the skin and oil droplets in the juice vesicles — and these two sources are usually quite distinct. Generally the vesicle oils contain more fruity esters, and peel oil more green aldehydes and citrusy/spicy terpenes (p. 274). A few aroma compounds are shared by most citrus fruit, including generically citrusy limonene and small amounts of eggy hydrogen sulfide. In freshly made juice, the sac oil droplets gradually aggregate with the pulpy materials, and this aggregation reduces the aroma available to the taster, especially if some of the pulp is strained off.

Citrus Peel The intensely flavored citrus peel has long been used to flavor dishes (for example, dried orange peel in Sichuan cooking), and as a preparation in itself in the form of candied rind. The outer epidermis contains the aromatic oil glands, while the underlying white, spongy, pectinrich albedo usually contains protective bitter phenolic substances. Both the oil with its terpenes and the antioxidant phenolics are valuable phytochemicals (pp. 256, 257). The bitters are water-soluble, while the oils are not. Cooks can therefore leach the peel repeatedly with hot (rapid) or cold (slow) water to remove the bitter compounds, then gently cook the peel if still necessary to soften the albedo, and finally infuse it with a concentrated sugar syrup. Through all this processing the water-insoluble oils stay largely in the rind. Marmalade, a sugar preserve that includes citrus peel, was originally a Portuguese fruit paste made with quince, but by the 18th century the high-pectin, readily gelled sour orange had begun to replace the quince. Marmalade made with sweet oranges doesn’t gel as readily and lacks the characteristic flavor, including a bitterness that helps balance the sugar.

As is true for most fruits, the skin of citrus fruits is more easily removed from the underlying tissue by briefly immersing the fruit in simmering water. Thick citrus rinds require an immersion of several minutes. Heat softens the cell-wall cement that attaches rind to fruit, and may also encourage some enzymes to begin to dissolve the cement.

Kinds of Citrus Fruits Trees in the genus Citrus are wonderfully variable and prone to form hybrids with each other, which makes it a challenge for scientists to work out family relationships. Currently it’s thought that the common domesticated citrus fruits all derive from just three parents: the citron Citrus medica, the mandarin orange Citrus reticulata, and the pummelo Citrus grandis. At least one offspring is relatively young: the grapefruit apparently originated in the West Indies in the 18th century as a cross between the pummelo and the sweet orange.

Citron Perhaps the first citrus fruit to reach the Middle East around 700 BCE and the Mediterranean around 300 BCE, citrons are native to the Himalayan foothills. They gave their name to the genus, and their name came in turn from their resemblance to the cone of a Mediterranean evergreen cedar (Greek kedros). The several varieties have little juice, but an intensely aromatic rind that can perfume a room — citrons are used in both Asian and Jewish religious ceremonies — and that has long been candied (p. 295). In China’s Sichuan province, the rind is made into a hot pickle.

Flavor Notes in Some Citrus Fruits

The chemicals listed in the first five flavor headings are terpenes, which are especially characteristic of citrus fruits and some herbs and spices (p. 390).

Mandarin, or Tangerine Mandarin oranges were cultivated in ancient India and China at least 3,000 years ago. The well-known Japanese type, the satsuma, appeared by the 16th century, and Mediterranean types (“tangerines,” from the Moroccan city of Tangier) in the 19th century. Mandarins tend to be relatively small and flat, with a reddish, easily peeled rind and a distinctive, rich aroma that has notes of thyme and Concord grape (thymol, methyl anthranilate). They’re the most cold-hardy of citrus trees, yet the fruits are fairly fragile. Satsumas are seedless and commonly processed into canned segments.

Pummelo Pummelos require the warmest growing conditions of the common citrus fruits and have been slow to spread from their home in tropical Asia, where they were cultivated in ancient times. They’re large, 10 in/25 cm or more in diameter, with a relatively thick albedo layer; large, easily separated juice vesicles that burst in the mouth; thick and tough segment membranes; and an absence of the bitterness that flavors its offspring the grapefruit. Some varieties have pink-red vesicles.

Orange Nearly three-fourths of all citrus fruit produced in the world are oranges, whose juiciness and moderate size, sweetness, and acidity make them especially versatile. They’re probably an ancient hybrid between the mandarin and the pummelo, and have in turn been developed into several very different kinds of fruit.

Navel oranges probably originated in China, but became a major commodity worldwide when a Brazilian variety arrived in the United States in 1870. The navel-like appearance of their blossom end is caused by the development of a small secondary set of segments. Navels are the ideal orange for eating fresh because they’re seedless and easily peeled. However, the trees are finicky to grow, and their juice contains fewer fruity esters than the best juice varieties. And juice made from navel oranges will become noticeably bitter after about 30 minutes. This happens because when the juice cells are broken and their contents mixed, acids and enzymes convert a tasteless precursor molecule into an intensely bitter terpene compound called limonin.

Citrus Family Relationships

The Parent Species

Citron

Citrus medica

Mandarin, tangerine

Citrus reticulata

Pummelo

Citrus grandis

Their Offspring

Sour orange

Citrus aurantium

Sweet orange

Citrus sinensis, pummelo x mandarin(?)

Grapefruit

Citrus paradisi, pummelo x sweet orange

Sour lime

Citrus aurantifolia

Persian/Tahiti lime

Citrus latifolia, sour lime x citron(?)

Lemon

Citrus limon, citron x sour lime x pummelo(?)

Meyer lemon

Citrus limon, lemon x mandarin or sweet orange?

Modern Hybrids

Tangelo

Citrus x tangelo, tangerine x grapefruit

Tangor

Citrus x nobilis, tangerine x sweet orange

Common or juice oranges have a smooth blossom end, generally contain seeds, and have a more adherent skin than navel oranges. Commercial orange juice is made from juice varieties with little tendency to develop limonin bitterness. The mild flavor of the juice is usually augmented by the addition of peel oils.

Blood oranges have been grown in the southern Mediterranean at least since the 18th century, and may have originated there or in China. They’re now the major type of orange grown in Italy. Blood oranges owe the deep maroon color of their juice to anthocyanin pigments, which develop only when night temperatures are low, in the Mediterranean autumn and winter. The pigments tend to accumulate at the blossom end and in vesicles immediately next to the segment walls, and continue to accumulate after harvest when the fruits are held in cold storage. The pigments and their phenolic precursors give blood oranges a higher antioxidant value than other oranges. The unique flavor of blood oranges combines citrus notes with a distinct raspberry-like aroma.

Acidless oranges are grown in small numbers in north Africa, Europe, and South America, and have about a tenth the acidity — and less orange aroma — of common and navel oranges.

Sour oranges come from a different species than the kinds described above, and are both sour and bitter (thanks not to limonin but a related compound, neohesperidin), with an intense and distinctive peel aroma. They arrived in Spain and Portugal in the 12th century, and soon displaced quince as the main ingredient in marmalade. Sour-orange flowers are used to make orange flower water.

Grapefruit The grapefruit originated as a hybrid of the sweet orange and pummelo in the Caribbean in the 18th century, and is still mainly grown in the Americas. The red types owe their color to lycopene, and first appeared as chance mutations in Florida and in Texas early in the 20th century (the more recent and popular Star Ruby and Rio Red varieties were created by intentionally inducing mutations with radiation). Unlike the anthocyanin coloration of blood oranges, grapefruit lycopene requires consistent high growing temperatures to develop well, appears evenly through all the juice vesicles, and is stable to heat. The characteristic moderate bitterness is caused by a phenolic substance called naringin, whose concentration declines as the fruit ripens. Like navel oranges, grapefruits also contain a precursor of limonin, and its juice becomes bitter on standing. Some grapefruit phenolic compounds turn out to interfere with our metabolism of certain drugs, cause the drugs to persist longer in the body, and thus cause the equivalent of an overdose, so medicine labels sometimes warn against consuming grapefruit or its juice along with the medicine. (These same phenolics are now being developed into activity-boosting drug ingredients.) Grapefruits have an especially complex aroma, which includes meaty and musky sulfur compounds.

Lime Limes are the most acidic of the citrus fruits, as much as 8% of their weight coming from citric acid. The small, seedy Mexican or Key lime, C. aurantifolia, is the standard sour citrus fruit in the tropics, where lemons don’t grow well. In western Asia it’s sun-dried whole, then ground and used as an aromatic, somewhat musty acidifier. The larger, seedless, more cold-tolerant Persian or Tahiti or Bearss lime, C. latifolia, may be a hybrid between the true lime and citron, and is more common in the United States and Europe. Despite the general impression that limes are characteristically “lime-green,” both turn pale yellow when fully ripe. They owe their distinctive limeness to pine, floral, and spicy aroma notes (from terpenes).

Lemon Lemons may have originated as a two-step hybrid, the first (citron crossed with lime) arising in the area of northwest India and Pakistan, the second ([citron crossed with lime] crossed with pummelo) in the Middle East. Lemons arrived in the Mediterranean around 100 CE, were planted in orchards in Moorish Spain by 400, and are now mainly cultivated in subtropical regions. They’re valued for their acidity, often 5% of the juice, and their fresh, bright aroma, which is the base for many popular fresh and bottled drinks. There are many varieties of true lemon, and also a couple of further hybrids. The large, coarse Ponderosa variety is probably a lemon-citron cross, and the Meyer lemon, a thin-skinned, less acid version brought to California in the early 20th century, is probably a cross between the lemon and either orange or mandarin, with a distinctive flavor due in part to a thyme note (from thymol). Lemons are generally “cured” for better shelf life; they’re picked green and held in controlled conditions for several weeks, where their skin yellows, thins, and develops a waxy surface, and the juice vesicles enlarge.

The preserved lemons of northern Africa have recently become more widely appreciated as a condiment. They’re made by cutting and salting lemons and letting them ferment for some weeks. The growth of bacteria and yeasts softens the rind and changes their aroma from bright and sharp to rich and rounded. Short versions of the process — for example, freezing and thawing the lemons to speed salt penetration, then salting for a few hours or days — will bring about some chemical changes as the oil glands are disrupted and their contents mix with other substances, but not the full flavor development of fermentation.

Other Citrus Fruits Lesser-known citrus fruits that are worth knowing about include the following:

• Bergamot, C. bergamia, possibly a cross between the sour orange and sweet lime (C. limettoides), is grown mainly in Italy for its floral-scented rind oil. It was one of the components of the original eau de cologne developed in 17th-century Germany, and is mainly used in perfumes, tobaccos, and Earl Grey tea.
• Kumquats, species of the genus Fortunella, are bite-size fruits that are eaten whole, thin rind and all. They are generally tart but not bitter. The calamondin or calamansi, also a diminutive citrus, is probably derived in part from the kumquat.
• The finger lime, Microcitrus australasica, is a small, elongated citrus relative native to Australia. Its fruit has robust, decorative round juice vesicles that can be pale or pink-red, and a distinctive aroma.
• The makrut or kaffir lime, Citrus hystrix, is common throughout Southeast Asia. Its rough green peel has a lime-like aroma with general citrus and pine notes (from limonene, pinene), and is used to flavor various prepared dishes, as are its intensely lemon-scented leaves (p. 410).
• The tangelo and tangor are modern hybrids between the tangerine and grapefruit, and tangerine and orange, with hybrid flavors as well, and mostly eaten as fresh fruit.
• The yuzu, Citrus junos, possibly a mandarin hybrid, came from China but was developed in Japan beginning around a thousand years ago. The rind of the small yellow-orange fruit is used to flavor various dishes, and to make vinegar, teas, and preserves. It has a complex flavor that includes musky sulfur compounds, and clove and oregano notes (from the phenolics eugenol and carvacrol).

Some Common Tropical Fruits

A century ago, only a handful of tropical fruits were available to Europe and North America, and they were luxuries. Nowadays the banana is a common breakfast food and new fruits appear in the market every year. Here are the most familiar.

Banana and Plantain Thanks to their productivity and starchy nutritiousness, bananas and plantains top the roster of world fruit production and trade. The worldwide annual per capita consumption is almost 30 lb/14 kg, and in regions where they’re a staple food, individuals consume several hundred kilograms per year. Bananas and plantains are the seedless berries of a tree-sized herb related to the grasses, Musa sapientum, which originated in the tropics of Southeast Asia. A banana plant produces a single flower structure with from 1 to 20 “hands” or fruit clusters, as many as 300 “fingers” of individual fruit, each fruit weighing from a couple of ounces to 2 lb/50–900 gm. The characteristic curve of long fruits develops because the fruit tip grows upward, against the downward pull of gravity. Bananas and plantains are climacteric fruits, store their energy as starch, and convert some or most of that starch to sugar during ripening. In the dramatic case of the banana, a starch-to-sugar ratio of 25 to 1 in the mature but unripe fruit becomes 1 to 20 in the ripe fruit.

The terms banana and plantain are used for two broad and overlapping categories for the many varieties of these fruits. Bananas are generally sweet dessert varieties, and plantains are starchy cooking varieties. Bananas are very sweet when ripe, their nearly 20% sugar content exceeded only by dates and jujubes, while ripe plantains may be only 6% sugar and 25% starch. Both are picked green and ripened in storage, and are very perishable once ripe thanks to their active metabolism. Bananas develop a meltingly smooth consistency, and a distinctive aroma due primarily to amyl acetate and other esters, and green, floral, and clove (eugenol) notes. Banana acidity also increases during ripening, sometimes twofold, so the flavor becomes more full in several dimensions. Ripe plantains generally retain a dry, starchy texture and can be treated as potatoes are, fried or mashed or cooked in chunks.

The pulp of these fruits is colored by carotenoids — plantain varieties often more noticeably — and tannins often make the unripe pulp astringent. Bananas and plantains are very prone to brown-black discoloration thanks to browning enzymes and phenolic substances in defensive latex-bearing vessels associated with the vascular system. These substances slowly decline by about half during ripening, so once a fruit is ripe, it can be refrigerated with relatively little discoloration of the flesh (the peel will still turn black).

Though a small handful of banana varieties (Grand Nain, Gros Michel, Cavendish) dominate in international trade, there are many interesting Latin American and Asian varieties to be found in ethnic markets, usually shorter, with tinted skin and flesh and intriguingly different flavors.

Cherimoya and Atemoya The cherimoya and atemoya are tree fruits of species in the genus Annona, a native of tropical and subtropical South America (the soursop or guanabana and the custard apple belong to the same genus). They are medium-sized masses of fused ovaries with their seeds, enclosed in inedible green or tan skins. Like pears, they can contain gritty stone cells. Cherimoyas and atemoyas are climacteric fruit that store starch and convert it to sugar during ripening; the result is a soft, sweet, low-acid flesh with about double the calories of common temperate fruits. They owe a vaguely banana-like note to esters, and flowery and citrus notes to a number of terpenes. They must be kept warmer than 55ºF/13ºC until they ripen, after which they can be refrigerated for a few days. Cherimoyas and atemoyas are eaten with a spoon both chilled and frozen, and are pulped and made into drinks and sorbets.

Durian Durian is the large, thorn-covered fruit of a tree, Durio zibethinus, that’s a native of Southeast Asia and cultivated mainly in Thailand, Vietnam, and Malaysia. Durian is notorious for its very unfruit-like aroma, a powerful smell that can be reminiscent of onions, cheese, and meat at various stages of decay! At the same time many people prize it for its delicious flavor and creamy, custard-like texture. The armored mass of fused ovaries, each containing a seed, can weigh more than 13 lb/6 kg, and apparently evolved to appeal to elephants, tigers, pigs, and other large jungle creatures, which are drawn to it by its battery of powerful sulfur compounds, including some found in onions, garlic, overripe cheese, skunk spray, and rotten eggs. These compounds are mainly found in the outer rind, while the fleshy segments surrounding the seeds are more conventionally fruity and savory, with an especially high content of sugars and other dissolved solids (36%). Durian is eaten as is, made into drinks, candies, and cakes, and incorporated into rice and vegetable dishes. It’s also fermented to make it even stronger-tasting (Malaysian tempoyak).

Guava and Feijoa Guavas are the large berries of a bush or small tree in the genus Psidium, a native of the tropical Americas, and a member of the myrtle family, which includes the clove, cinnamon, nutmeg, and allspice trees. True to their family background, they have a strong, spicy/musky aroma (from cinnamate esters and some sulfur compounds). Their flesh contains hundreds of small seeds and many gritty stone cells, so guavas are most often used to make purees, juices, syrups, and preserves. The Spanish colonizers exploited their high pectin content to make a New World version of quince paste. Guavas are remarkable for a vitamin C content that can reach 1 gram per 100 grams, with much of it concentrated near and in the thin, fragile peel.

The so-called pineapple guava, or feijoa, comes from the shrub Feijoa sellowiana, also a South American member of the myrtle family. It shares a similar size and structure and some flavor elements with guava, but its strong aroma is distinctive and less complex, dominated by a particular group of esters (from benzoic acid). It too is usually pulped and strained for use in liquid preparations.

Breadfruit and Jackfruit Breadfruit and jackfruit are fruits of two species of the Asian genus Artocarpus, a relative of the mulberry and fig, and resemble each other in structure. They’re very large assemblies of fused ovaries and their seeds; breadfruits may reach 9 lb/4 kg, and jackfruits 10 times that weight. Jackfruit, a native of India, has a conventional composition for a fruit — mostly water, with 8% sugar and 4% starch — and develops a strong, complex aroma with musky, berry, pineapple, and caramel notes. It’s eaten raw and in ice creams, as well as dried, preserved, and pickled. Breadfruit, whose origins in the Pacific islands remain unclear, gets its name from its very high starch content, as much as 65% by weight (with 18% sugar and just 10% water) when mature but unripe, and when cooked into a dry, absorbent mass. It’s a staple food in the South Pacific and in the Caribbean, where it was taken by Captain Bligh of the notorious Bounty mutiny. It may be boiled, roasted, fried, or fermented into a sour paste, then dried and ground into flour. Ripe breadfruit is sweet and soft, even semiliquid, and made into desserts.

Lychee Lychees are subtropical Asian tree fruits (from Litchi chinensis) the size of a small plum, with a dry, loose skin and a large seed. The edible portion is its fleshy seed covering, or aril, which is pale white, sweet, and distinctively floral due to the presence of a number of terpenes (rose oxide, linalool, geraniol; Gewürztraminer grapes and wine share many of the same notes). Lychees with small, undeveloped seeds are called “chicken-tongue” fruit and are prized because there’s more flesh than seed. Lychees don’t improve in flavor once taken from the tree. A common problem with lychees is a brown discoloration of the flesh due to drying out or chilling injury. They’re best held at cool room temperatures in a loose plastic bag. When cooked, fresh lychees sometimes develop a pink undertone as phenolic aggregates are broken apart and converted into anthocyanin pigments (p. 281). They’re eaten fresh, canned in syrup, made into drinks, sauces, and preserves, cooked briefly and served with meats and seafood, and frozen into sorbets and ice creams. “Lychee nuts” are the dried fruits, not the seeds.

Rambutans, longans, and pulasans are all arils of Asian fruits in the same family as the lychee (the Sapindaceae), and have similar qualities.

Mango Mangoes are the succulent, aromatic fruits of an Asian tree, Mangifera indica, a distant relative of the pistachio and cashew trees, that has been cultivated for many thousands of years. There are hundreds of varieties with very different qualities, including flavor and degrees of fibrousness and astringency. The mango skin contains an irritant and allergenic phenolic compound similar to that in the cashew. Their deep orange color comes from carotenoid pigments, mainly betacarotene. Mangoes are climacteric fruits that accumulate starch, so they can be picked green and will sweeten and soften as they ripen, from the seed outwards. Their flavor is especially complex, and may be dominated by the compounds that characterize peaches and coconuts (lactones), generically fruity esters, medicinal or even turpentiny terpenes, and caramel notes. Green mangoes are very tart, and are made into pickles as well as dried and ground to make an acidifying powder (Hindi amchur). Mango pickles were so admired in 18th-century England that the fruit lent its name to the preparation and to other suitable materials: hence “mango peppers.”

Mangosteen The mangosteen is the medium-sized, leathery-skinned fruit of an Asian tree, G arcinia mangostana. Its white flesh consists of the arils around several seeds, and is moist and has a pleasing sweet-tart balance, with a delicate, fruity and flowery aroma, something like a lychee. It’s usually eaten fresh or in preserves, and is also canned.

Papaya Papayas are species of the genus Carica, a native of the American tropics that looks like a small tree but is actually a large herbaceous plant. The common papaya, C. papaya, consists of a thickened ovary wall, orange to orange-red with carotenoid pigments, and a few dark seeds in a large central cavity. It is a climacteric fruit that doesn’t store any starch. Ripening begins at the center and progresses outward, and causes a manyfold increase in carotenoid pigments and aroma molecules, as well as a marked softening. Softening causes the apparent sweetness to increase even though the actual sugar content doesn’t change (the sugars are more readily released from the softened tissue). A ripe papaya is a low-acid fruit with a delicate, flowery aroma thanks to terpenes, and a touch of cabbage-like pungency due to the surprising presence of isothiocyanates (p. 321). These compounds are especially concentrated in the seeds, which can be dried and used as a mildly mustardy seasoning.

Unripe, crisp green papaya is made into salads and pickles. The green fruit contains vessels of milky latex rich in the protein-digesting enzyme papain, which is found in some meat tenderizers. Papain levels drop during ripening, but can still cause texture and taste problems like those caused by the pineapple enzyme bromelain (p. 384).

Two other papaya species can be found in markets. The large cool-climate mountain papaya, C. pubescens, is less sweet than the lowland papaya, but richer in papain and in carotenoid pigments, often including lycopene, which gives its flesh a reddish tinge. The babaco, C. pentagona, is apparently a natural hybrid, and has cream-colored, tart, seedless flesh.

Passion Fruit, Granadilla Passion fruits and the granadilla come from about a dozen species of vines of the genera Passi-flora and Tacsonia, natives of tropical lowlands and subtropical highlands in South America. They consist of a brittle (Passi-flora) or soft (Tacsonia) outer husk, with a mass of hard seeds embedded in pulpy seed coverings, or arils. The arils are the only edible portion, and make up barely a third of the fruit weight. Though the pulp is sparse, its flavor is concentrated and actually benefits from dilution. Passion fruits are unusual for their relatively high acid content, mainly citric — more than 2% of the pulp weight in purple-skinned types, and double that in most yellow ones — and their strong, penetrating aroma, which appears to be a complex mixture of fruity and flowery notes (esters, peach-like lactones, violet-like ionone), and unusual musky notes (from sulfur compounds like those in black currants and sauvignon blanc wines). Passion fruit pulp is used mainly to make beverages, ices, and sauces, with the milder purple P. edulis generally consumed fresh and the stronger yellow P. edulis var. flavicarpa processed (an early commercial application was Hawaiian punch).

Pineapple Pineapples are the large, pinecone-like fruit of Ananas comosus, a member of the bromeliad family (which includes bromeliad houseplants) and native to tropical but arid South America. (Ananas comes from a Guarani Indian word for the fruit; pineapple from the Spanish piña due to its resemblance to the similarly composite pinecone.) The plant had already spread to the Caribbean before Columbus saw it there in 1493, and modern breeding efforts began shortly thereafter in French and Dutch glasshouses.

Pineapples consist of spirals of separate seedless fruitlets, between 100 and 200 of which fuse together and become joined to a central core. During the fusing process, bacteria and yeasts become incorporated in the interior and may later cause hidden spoilage. The fruit doesn’t store starch, is not a climacteric fruit, and will not sweeten or improve in flavor once picked, though it will soften. Fully ripe pineapples don’t ship well, so exported pineapples are harvested early, with as little as half the sugar content that they’re capable of developing, and a fraction of the aroma. Brown or black regions in the interior are caused by chilling injury during shipment or storage; translucent areas seem to be caused by growing conditions that load the fruit cell walls with sugars. The quality of pineapples from the subtropics is less reliable than that of fruit from near the equator, where seasonal and climatic variation is minimal.

Pineapple Flavor Pineapples are remarkable for the intensity of their flavor, the experience of which the 19th-century English writer Charles Lamb described as “almost too transcendent…a pleasure bordering on pain, from the fierceness and insanity of her relish.” At their best they are both very sweet and quite tart (from citric acid), and with a rich aroma provided by a complex mixture of fruity esters, pungent sulfur compounds, essences of vanilla and clove (vanillin, eugenol), and several oxygen-containing carbon rings with caramel and sherry overtones. A given pineapple has many different flavor zones. The fruitlets near the base form first and are therefore the oldest and sweetest, and the acidity of the flesh doubles from the core to the surface. Thanks to their assertive flavor and firm, somewhat fibrous flesh, pineapples can be cut into chunks and baked, grilled, or fried. They have an affinity for the flavors of butter and caramel and work well in baked goods, as well as various raw preparations (salsas, drinks, sorbets).

Pineapple Enzymes Pineapples contain several active protein-digesting enzymes that are used in meat tenderizers, but can cause problems in other prepared dishes. (In medicine they have been exploited as a means of cleaning burns and other wounds, and they help control inflammatory diseases in animals.) Bromelain, the major enzyme, will break down gelatin, so pineapple for gelatin-based desserts must be cooked first, to inactivate the enzyme. And if incorporated into a mixture containing milk or cream, bromelain will break down the casein proteins and produce bitter-tasting protein fragments. Again, precooking the pineapple will prevent this.

Star Fruit Star fruit or carambola come from the small Southeast Asian tree Aver-rhoa carambola, a member of the wood sorrel (Oxalis) family. These medium-sized, yellowish fruits are notable for their starlike cross section, a decorative touch in salads and garnishes, for an aroma with notes of Concord grapes and quince, and for the presence of oxalic acid, mainly in the five ridges. When unripe and especially rich in oxalic acid, star fruit are sourly reminiscent of similarly endowed sorrel (p. 411) and are used to clean and polish metal! Star fruit are colored by carotenoid pigments, including beta-carotene. A relative, the bilimbi, is too tart to eat fresh and in the tropics is made into preserves and drinks.