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Curdling Milk: RENNET, ren'et, the lining membrane of the fourth stomach of unweaned mammals ; particularly the prepared contents from the lining membrane of a young calf. It contains the enzyme rennin, which has the property of curdling milk. Rennet is now commercially prepared. It is important in making cheese and coagulating casein for plastics, as well as in medical and pharmaceutical preparations.
Despite these variations, the basic method of cheese-making is the same everywhere. A curdling agent is added to the milk to precipitate the solids. (The solidified casein, fat and other water insoluble constituents are called the curds, and the remaining liquid is known as whey.) The curds are broken or cut to release most of the whey and left to drain. They are then broken up, salted and put into moulds. Finally the cheese is ripened.
All cheese starts as milk, but the milk may be sweet whole milk, a combination of sweet and sour milk, or a mixture of whole and skim milk. The first step in making cheese is to separate the whey (the liquid portion of the milk) from the curd (the solid particles). When milk is slightly sour, this may be done by placing the milk over very low heat for several hours. In modern manufacture, a culture of lactic acid-producing bacteria is added to sweet milk to cause the separation, and sometimes a combination of heat plus the culture and an extract of rennet may be used. |
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