Cheese is a foo made from milk, usually the milk of cows, buffalo, goats, or sheep, by coagulation. The milk is acidified, typically with a bacterial culture, then the addition of the enzyme rennet or a substitute (e.g. acetic acid or vinegar) causes coagulation, to give "curds and whey". Some cheeses also have molds, either on the outer rind (similar to a fruit peel) or throughout.