Rennet, also called chymosin (bovine chymosin: PDB1CMS, EC 3.4.23.4), is an enzyme that is added to milk as the first step in making cheese, or for making junket. The enzyme converts calcium caseinate particles in the milk to relatively insoluble calcium paracaseinate, which in the presence of calcium ions coagulates to form a curd.
The traditional source of rennet is the abomasum (fourth stomach) of slaughtered new-born calves or other young ruminants. It is also possible to produce rennet from fungi. In recent times, most commercial rennet is made from genetically modified yeast or bacteria, allowing the production of cheese that is considered vegetarian. This rennet is typically of a greater quality and consistancy than traditional animal rennet.
