Wikipedia Article About Vegetable rennet on Wikipedia The active enzyme in rennet is called rennin or chymosin (EC 3.4.23.4). The chief use of rennet is in the making of cheese and junket. The enzyme reacts with κ-casein on the surface of the casein micelle particles in the milk. This in the presence of calcium ions causes the coagulation of the casein micelles to form a curd. Commercially, rennet is sold in liquid, powder, and tablet forms.