Cheese is a solid food made from the curdled milk of cows, goats, sheep, or other mammals. The milk is curdled using some combination of rennet and acidification. Bacteria acidify the milk and play a role in defining the texture and flavor of most cheeses. Some cheeses also feature molds, either on the outer rind or throughout.
There are hundreds of types of cheese. Different styles and flavors of cheese are the results of using different species of bacteria and molds, different levels of milk fat, variations in length of aging, and differing processing treatments.
Cheeses are eaten raw or cooked, alone or with other ingredients. As they are heated, most cheeses melt and brown. Some cheeses melt smoothly, especially in the presence of acids or starch. Cheese fondue, with wine providing the acidity, is a good example of a smoothly-melted cheese dish. Other cheeses turn elastic and stringy when they melt, a quality that can be enjoyed in dishes like pizza.