Rennet is an aspartic protease first found in the stomach of unweaned calves. It can specifically cleave the peptide bond between Phe105-Met106 of κ-casein in milk and destroy casein micelles. Milk coagulation, rennet's coagulation ability and proteolytic ability make it a key enzyme in the formation of texture and special flavor in cheese production. It is widely used in the production of cheese and yogurt.