Cheese is a dairy product produced in wide ranges of flavors, textures, and forms by coagulation of the milk protein casein. It comprises proteins and fat from milk (usually the milk of cows, buffalo, goats, or sheep). During production, milk is usually acidified and either the enzymes of rennet or bacterial enzymes with similar activity are added to cause the casein to coagulate. The solid curds are then separated from the liquid whey and pressed into finished cheese. Some cheeses have aromatic molds on the rind, the outer layer, or throughout.

Over a thousand types of cheese exist and are produced in various countries. Their styles, textures and flavors depend on the origin of the milk (including the animal's diet), whether they have been pasteurized, the butterfat content, the bacteria and mold, the processing, and how long they have been aged. Herbs, spices, or wood smoke may be used as flavoring agents. The yellow to red color of many cheeses is produced by adding annatto. Other ingredients may be added to some cheeses, such as black pepper, garlic, chives, or cranberries. A cheesemonger, or specialist seller of cheeses, may have expertise with selecting, purchasing, receiving, storing and ripening cheeses.

For a few cheeses, the milk is curdled by adding acids such as vinegar or lemon juice. Most cheeses are acidified to a lesser degree by bacteria, which turn milk sugars into lactic acid, then the addition of rennet completes the curdling. Vegetarian alternatives to rennet are available; most are produced by fermentation of the fungus Mucor miehei, but others have been extracted from various species of the Cynara thistle family. Cheesemakers near a dairy region may benefit from fresher, lower-priced milk, and lower shipping costs.

Cheese is valued for its portability, long shelf life, and high content of fat, protein, calcium, and phosphorus. Cheese is more compact and has a longer shelf life than milk, although how long a cheese will keep depends on the type of cheese. Hard cheeses, such as Parmesan, last longer than soft cheeses, such as Brie or goat's milk cheese. The long storage life of some cheeses, especially when encased in a protective rind, allows selling when markets are favorable. Vacuum packaging of block-shaped cheeses and gas-flushing of plastic bags with mixtures of carbon dioxide and nitrogen are used for storage and mass distribution of cheeses in the 21st century. Plant-based cheese has a lower carbon footprint.

Molds are used to make certain kinds of cheeses and can be on the surface of cheese or be developed internally. Blue veined cheese such as Roquefort, blue, Gorgonzola, and Stilton are created by the introduction of Penicillium roqueforti or Penicillium roqueforti spores. Cheeses such as Brie and Camembert have white surface molds. Other cheeses have both an internal and a surface mold. The molds used to manufacture these cheeses are safe to eat.

Some molds are used to make certain kinds of cheeses including (Roquefort, blue, Gorgonzola, Stilton, Camembert, and Brie). The mold on these cheeses is safe to eat. Mold on other types of cheeses should not be there. Discard any soft cheese showing mold. For hard cheese, such as Cheddar, cut off at least 1-inch around and below the mold spot (keep the knife out of the mold itself). After trimming off the mold, the remaining cheese should be safe to eat. Re-cover the cheese in fresh wrap and keep refrigerated. Exceptions: Some salamis,San Francisco, Italian and Eastern European types, have a characteristic thin, white mold coating; they shouldn't show any other mold. Dry cured country hams have surface mold that must be scrubbed off before cooking. Discard any soft fruits or vegetables, jams and jellies, bread, and baked goods that have mold.

Unpasteurized milk, cheese and other dairy products may contain harmful pathogens and are not safe to eat, drink, or use in making foods. It is a violation of federal law enforced by the Food and Drug Administration to sell raw milk packaged for consumer use across state lines (interstate commerce). Each state, however, regulates the sale of raw milk within the state (intrastate), and some states allow it to be sold. This means that in some states dairy operations may sell it to local retail food stores or to consumers directly from the farm or at agricultural fairs or other community events, depending on the state law.

Soft cheeses such as cream cheese, cottage cheese, shredded cheeses, and goat cheese must be refrigerated for safety. As a general rule, hard cheeses such as cheddar, processed cheeses (American), and both block and grated Parmesan do not require refrigeration for safety, but they will last longer if kept refrigerated.

REFRIGERATOR:

Approximate storage times are:

• (1) Hard cheeses (block): 6 months, unopened packages; 3 to 4 weeks after opening. Shredded hard cheeses: 1 month after opening.
• (2) Soft cheeses: 1 week; cream cheese, 2 weeks.

FREEZER:

Ricotta, cottage, and cream cheeses do not freeze well. Other cheeses may be frozen for 6 months.