Rust is probably the most visible example of oxidation, which is literally the burning of iron with oxygen. The rusty scales are the ash of this slow-motion blaze, but oxidation is occurring everywhere you look. Our bodies, for example, rely on oxidation to burn glucose and create the ATP that fuels us. In the kitchen, oxidation is often a problem. Rancid-smelling food or browned fruit, for example, are often telltale signs of oxidation at work. You may not realize it, but when you open a package of, say, cereal, the “air” inside is really nitrogen or some other mostly inert gas. If it were regular air, the oxygen would ruin your Chocolate Frosted Sugar Bombs.

But oxidation isn’t always bad. When skillfully managed, oxidation imbues dry-aged meat with its characteristic nutty aroma. The flavor of cured meats like country ham wouldn’t be the same without oxidation, and cheese just wouldn’t be cheese.