MODEL RELEASED. Cheese manufacture. Man adding a bowl of rennet to a vat of milk during cheese manufacture. This is the first process of cheese making during which the milk is left to curdle in a warm place. As milk curdles the solid part, or curd, separates out from the liquid part, or whey. The curd is later drained, salted, moulded and matured to make the finished product. Rennet is a substance found in the stomachs of animals which drink milk. It contains an enzyme called rennin or chymosin which coagulates milk. Rennin is often added during cheese manufacture to pasteurised milk to speed up the curdling process. Photograph taken in Bavaria, Germany.