chymosine

Chymosin, traditionally known as rennet, is an aspartic protease enzyme used to coagulate milk in cheese production. It is found in the stomach lining of young ruminant animals, most commonly calves, and has been used in cheesemaking for centuries.

Chymosin cleaves κ-casein at the Phe105–Met106 bond on the surface of casein micelles, removing the stabilizing tail and destabilizing the micelles. The resulting gel formation yields curd and whey, enabling the production of cheese.

Traditionally, chymosin was obtained from calf abomasae. In modern industry it is produced by microbial fermentation using genetically engineered microorganisms, creating recombinant chymosin that is chemically identical to the animal-derived enzyme and widely used as a vegetarian alternative.

Chymosin belongs to the pepsin-like family of aspartic proteases. It is used as the primary coagulant in many cheeses, often in blends with other agents to adjust texture and flavor. Regulatory agencies consider it safe for use in food, and recombinant forms are common in global cheesemaking.