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.
Some think rennets preserved in this way are not as strong as those that are dried. We do not quite see the philosophy of this, since by packing in salt, none of the virtues of the rennet can escape by evaporation, and must be retained either in the rennet or in the salt. It may be said that the salt injures the strength of the rennet. If so, why does it not prove equally injurious when the rennet is dried? In both methods of preserving, salt is freely used—generally all that the rennet will absorb. A batch of dried rennets may go farther than the same number packed in salt, and vice versa; but this does not prove that the same rennets would not have equal virtues preserved by either method.
The German method of preserving rennets is by blowing them up like a bladder, and drying them. This is the way in which the Bavarian rennets, which reach this country, are preserved. We believe no salt is used. The method is simple, and if it answers the purpose equally well, we see not why it may not be adopted in this country. We understand that the Bavarian rennets give very good satisfaction. But, as we have never used them, nor seen them used, we cannot speak from positive knowledge.
Veal rennets are generally supposed to be better than deacon rennets. Certain it is that the stomach of a calf that never sucked the cow is not worth much in cheese-making. It is both small and weak. It seems to be necessary that the process of digestion should go on for a while, at least, that all the functions of the animal may become active and a full secretion of gastric juice take place. Some are of the opinion that the rennet is best when the calf is from three to five days old, as at that age it is not likely to have taken anything but milk into its stomach, which is best prepared for digesting that kind of food, the first process of which is coagulation. Veal calves are apt to get hold of other food, and the stomach is therefore less exclusively adapted to a milk diet. Hence, it is argued, if the veal rennet is better than the deacon, the stomach of the cow or ox ought to be better than that of the veal calf. Whatever may be the conclusion, we have, and shall probably continue to have, both deacon and veal rennets, both kinds of which have been found to work satisfactorily.
Much seems to depend on the condition of the calf when killed. If it goes too long without food, the stomach gets inflamed and is not only deprived of its strength, but is partially diseased, and, therefore, unfit for cheese-making. This is the condition of most of the rennets taken from calves killed in our larger cities, the calves going without food sometimes two or three days. On the other hand, when the calf has a full stomach, the juices seem to be absorbed in the food, and the rennet is, therefore, weak. The best time for killing the calf appears to be just after the stomach has emptied itself, when the appetite of the calf begins to be sharp and the secretions of gastric juice are copious. This will generally be found from twelve to eighteen hours after eating. If fed at night, it may be killed any time the next forenoon.