The milk of various animals has been used in the making of cheese: the milk of mares and goats by the ancient Greeks, camel's milk by the early Egyptians, and reindeer's milk by the Laplanders. Sheep's milk and goat's milk are still widely used, but cow's milk is most common. The milk may be raw or pasteurized, sweet or sour, whole, skimmed, or with cream added.
Cheese, especially in the United States, is increasingly made in the factory by application of the principles of microbiology and chemistry. The chief milk protein, casein, is coagulated by the enzyme action of rennet or pepsin, by lactic acid produced by bacterial action, or by a combination of the two. The draining off of the whey (milk serum) is facilitated by heating, cutting, and pressing the curd. The yield of cheese is usually about 10 lb per 100 lb of milk and is higher for the soft cheeses, which retain more moisture. Wisconsin is the largest producer of cheese in the United States.
The byproduct whey consists of water, lactose, albumin, soluble minerals, fats, and proteins. Formerly wasted or used in livestock feeding, whey is now used for the preparation of milk sugar, lactic acid, glycerin, and alcohol, or is condensed and added to process cheese. It may be made into cheese such as the Scandinavian primost and mysost.