Dairy Buzz

Rennet is a proteolytic enzyme that is used mainly to make cheese. On its addition to milk, it coagulates or converts the casein micelles into a curd with whey separating from the mass.

There are mainly three different types of commercial preparations of rennet:

a) Animal Rennet – This is rennet in its natural form which is extracted from the stomachs of young calves. The active ingredient in this rennet is called chymosin. Until the early 1990s, most of the cheese produced worldwide was made with animal rennet. Animal rennet is normally supplied in liquid form. It is also offered as tablets to small cheese producers. Apart from chymosin, animal rennet also contains small quantities of pepsin and traces of lipase and other impurities. However strong resistance to its use from vegetarians and other animal welfare groups caused the development of factory produced alternatives such as microbial rennet and fermentation produced chymosin.

b) Microbial Rennet – It is sourced from fungi, bacteria and other microorganisms that produce chymosin. The most widely produced microbial rennet is made from the mold Mucor Meihei. It is sold in liquid, powder or granular form. The major disadvantage of microbial rennet is that the cheese tends to develop bitterness, especially those that need long ripening periods. Cheese yields with microbial rennet also tend to be marginally lower than those produced with chymosin.

c) Fermentation produced chymosin – these are produced from genetically modified organisms that yield chymosin that is 100% pure and identical to the chymosin found in animal rennet. This rennet is cheaper and, unlike calf rennet, is plentiful. The most widely used such chymosin today is produced from the fungus Aspergillus niger.

A few commercially available microbial rennet and fermentation produced chymosin preparations have received vegetarian certification.