There are three or four ways of preserving the rennet or stomach, for future use. Only two, we believe, are generally practiced in America. In all cases, the rennet is to be turned wrong side out, all its contents being thrown away, and the inner surface carefully cleaned by picking off all hairs and bits of grass, hay or other substance which the calf may have taken into its stomach. But the rennet should never be washed, and great care should be taken not to remove any of the inner membrane of the rennet, as in this membrane resides all its strength. Washing would rinse out the gastric juice, and weaken the rennet; and much washing would render it nearly or quite worthless.
When properly cleaned, the rennet should be thoroughly rubbed with salt, outside and in, turned the right side out, stretched on a crotched stick or on a hoop, and hung up in a cool, dry place, to cure. In private dairies, the farmer's wife, after salting the rennet, sometimes spreads it on an earthen plate and sets it away to dry, frequently turning it on the plate. Rennets dried in this way are nice, but it is too much work to tend to them for a general adoption of this method of drying. Drying on a stick or a hoop is the common way, and answers the purpose very well. The only trouble is to find a place both dry and cool. It is generally conceded, we believe, that heat injures the strength of the rennet. Hence the importance of curing it in a cool place. Freezing is thought by many to add to or develop the strength of the rennet. Be this as it may, old rennets, that have hang up in the dry-house or some other convenient place through the winter, will go much further in cheese-making than new rennets.
Another method of preserving rennets is by packing them into salt. This is quite common, and is practiced by some of our best factories. It is less troublesome than drying them, and is a sure preventive against moths, which are apt to get into dried rennets. By salting them down, there is less trouble to find a cool place in which to keep them during the summer. But care should be taken to use only the purest salt in packing rennets. Salt not fit to salt curd with is not fit to pack rennets in, for when the rennets are used, the salt will be in the liquid and find its way into the mass of curd. Besides, pure salt is much the better preservative, and will keep either meat or rennets sweeter than impure salt.