Cheese is a solid food made from the milk of cows, goats, sheep and other mammals, by coagulating the milk. This is accomplished by first acidification with a bacterial culture and then employing an enzyme, rennet (or rennet substitutes) to coagulate the milk to "curds and whey." The precise bacteria and processing of the curds play a role in defining the texture and flavor of most cheeses. Some cheeses also feature molds, either on the outer rind or throughout.