Rennet
The enzyme preparation that makes milk set into a firm curd, the key ingredient in most aged cheeses.
Also: coagulant, presure, caglio, Lab
Rennet is any preparation of enzymes that coagulates milk. Its active part, usually chymosin, makes a precise cut in milk's casein so that it knits into a firm, elastic gel that can be cut, drained and aged. Rennet once meant only an extract of the stomach lining of young calves, kids or lambs, but today it also includes microbial rennet from moulds, fermentation-produced chymosin, and plant coagulants such as cardoon thistle, fig sap and the berries of Withania coagulans, the paneer dodi of north-west India. Only a few drops are needed per litre. Fresh acid-set cheeses such as paneer use no rennet, which is one reason they do not melt.