Rennet, also called rennin or chymosin (EC 3.4.23.4 http://www.expasy.org/cgi-bin/nicezyme.pl?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, milk-fed 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 thought to be of a greater quality and consistency than traditional animal rennet.

Sometimes, the terminology is more distinct, rennet being the stomach extract, while rennin or chymosin are names for the pure enzyme itself, which is the active ingredient in the extract.

See also: pepsin

External links

• http://www.vegsoc.org/info/cheese.html
• PDB 1CMS http://www.rcsb.org/pdb/cgi/explore.cgi?pid=203441034360021&page=0&pdbId=1CMS , bovine chymosin