rennet, substance containing rennin, an enzyme having the property of clotting, or curdling, milk. It is used in the making of cheese and junket. Rennet is obtained from the stomachs of young mammals living on milk, especially from the inner lining of the fourth, or true, stomach (abomasum) of milk-fed calves. The preparation of rennet was formerly a part of the domestic function of making cheese; the inner membrane was kept in salt, dried, and, when rennet was needed, soaked in water. Now extract of rennet is made and sold commercially. It is usually prepared by soaking the tissues in warm, slightly salted water and straining and preserving the resulting liquid. Heat interferes with the action of rennet.

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