Chymosin or rennin is a protease found in rennet. It is produced by newborn ruminant animals in the lining of the fourth stomach to curdle the milk they ingest, allowing a longer residence in the bowels and better absorption. It is widely used in the production of cheese. Bovine chymosin is now produced recombinantly in , Aspergillus niger var awamori, and as alternative resource.