Cheese is a fermented food derived from the milk of various mammals. Since humans began domesticating milk-producing animals around 10,000 BC. they already knew about the tendency of milk to separate into curds and whey. When milk becomes sour, it breaks down into curds, phosphoprotein clumps and whey, a gray, watery liquid that contains lactose, minerals, vitamins and traces of fat. The curds are used to make cheese, and almost every culture on Earth has its own method, the only major exceptions being China and the ancient Americas.

Cheese is made from cow's milk, which comes from a variety of animals such as cows, sheep, goats, horses, camels, buffalo and reindeer. Most cheese makers use rennet, lactic acid, or plant extracts (such as plant rennet made from wild artichoke, fig leaf, safflower, or melon) to speed up the curdling process.

In addition to milk and rennet, cheese may contain a variety of added ingredients to enhance flavor and color. The world's best cheeses may get their flavor from the specific bacterial molds they are inoculated with, an example being the famous Penicillium roqueforti used to make Roquefort in France and Stilton in the U.K. Cheeses can also be salted or dyed, often with cochineal, an orange pigment made from the pulp of the Tropicana tree, or carrot juice. They can be washed in brine or covered with ash. Cheese makers who wish to avoid rennet may promote the growth of the bacteria needed for curdling by many strange methods. Some cheeses contain this bacteria because they are made from unpasteurized milk. Yet other cheeses are reportedly made from milk soaked in feces or old leather; still others have contracted the bacteria from being buried in mud.

The unusual texture and flavor of processed cheese is obtained by blending several natural cheeses and adding salt, milk fat, cream, whey, water, vegetable oils and other fillers. Processed cheeses will also contain ingredients such as preservatives, emulsifiers, gum, gelatin, thickeners and sweeteners. Most processed cheeses and some natural cheeses are flavored with ingredients such as paprika, peppers, fine shallots, onions, cumin, caraway, jalape?os, hazelnuts, raisins, mushrooms, sage, and bacon. Cheese can also be smoked to preserve it and give it a unique flavor.