Rennet Coagulation

Rennet coagulation is the cheesemaking technique of curdling milk using rennet, a set of enzymes from the stomachs of ruminant mammals whose key component, chymosin, is a protease that acts on the casein proteins in milk. Chymosin cleaves a fragment called glycomacropeptide from the surface of the milk's casein micelles; because that fragment carries a negative charge that normally keeps the micelles apart, removing it lets the micelles clump together, separating the milk into solid curds and liquid whey. Rennet coagulation is a traditional step in cheese production, though most cheese today is made with chymosin from bacterial sources rather than rennet taken directly from calves.