<P> Rennet / ˈrɛnɪt / is a complex of enzymes produced in the stomachs of ruminant mammals . Chymosin, its key component, is a protease enzyme that curdles the casein in milk . This helps young mammals digest their mothers' milk . Rennet can also be used to separate milk into solid curds for cheesemaking and liquid whey . In addition to chymosin, rennet contains other important enzymes such as pepsin and a lipase . </P> <P> Rennet is used in the production of most cheeses . The mammal's digestive system must be accessed to obtain its rennet . Non-animal alternatives for rennet are also available . </P> <P> Calf rennet is extracted from the inner mucosa of the fourth stomach chamber (the abomasum) of young, unweaned calves as part of livestock butchering . These stomachs are a byproduct of veal production . If rennet is extracted from older calves (grass - fed or grain - fed), the rennet contains less or no chymosin, but a high level of pepsin and can only be used for special types of milk and cheeses . As each ruminant produces a special kind of rennet to digest the milk of its own species, milk - specific rennets are available, such as unweaned goat rennet for goat's milk and lamb rennet for sheep's milk . </P> <P> Dried and cleaned stomachs of young calves are sliced into small pieces and then put into salt water or whey, together with some vinegar or wine to lower the pH of the solution . After some time (overnight or several days), the solution is filtered . The crude rennet that remains in the filtered solution can then be used to coagulate milk . About 1 g of this solution can normally coagulate 2 to 4 L of milk . </P>

Where do the enzymes in cheese come from