In saving rennets, great care should be taken to have them right.
The fourth stomach of the calf is what is saved. Cut it from the
adjoining stomach, at the point of junction, and do not leave a piece
of intestine on the other end, but cut close to the opening of the
rennet. Remove straws and dirt of all kinds carefully, but be sure to
not rub off the delicate lining of the stomach, which is the digestive
or coagulative part and very much inclined to adhere to your hands,
especially if they are dry. Do not try to rinse off anything more
than the loose dirt, and that without rubbing, for you cannot rub
without waste. What is better, avoid having dirt or any thing else in
the stomach to remove. This you can do by letting the calf go sixteen
or eighteen hours without eating, and placed where it can get hold
of nothing to swallow before killing. Say, feed it at night and slay
it the next day about noon. The stomach will then be empty and clean
and well stored with pepsin for the digestion of the next meal. This
secretion, is just what you want. The rennet is best when the calf
is six or eight days old. But, in any case, digestion should be well
established before killing. If the calf should go too long without
food--as is often the case with veal calves--the stomach will get
inflamed. This is objectionable.