Rennet

Rennet (A.S. rinnan, rennan, 'to run') consists of the inner lining of the true stomach (see DIGESTION) of the sucking-calf. It contains a ferment which causes milk to clot (see MILK), called the milk-curdling-ferment. The rennet is used in the manufacture of cheese, and to a less extent in the preparation of curds and whey or junket. It is prepared by removing the stomach from the calf as soon as it has been killed, and separating off the lining membrane of the stomach. It is then salted and dried, and will keep for some time in that condition. When used, a small piece of the rennet, in which the ferment is still quite active, is softened in water and added to the milk which is to be curdled. For many years past the milk-curdling-ferment has been obtained from rennet in the form of an extract. It is soluble in salt and water, and is extracted from the fresh rennet of the calf, and kept from putrefying by the addition of alcohol. Extracts of rennet thus prepared are extensively used, and may be had at the druggists' stores.