RENNET AND ITS PREPARATION.

Globe, Volume IX, Issue 1225, 6 February 1878, Page 3

RENNET AND ITS PREPARATION.

The manufacture of cheese depends upon the peculiar property pos»es°ed by casein of being curdled by acids. On the addition of an acid to milk, the casein, or cheesey portion, which constitutes three-fourths of the nitrogenous matter present, is separated from liquid, and this separation of milk into curds and whey is the first step in cheesemaking. Curd may be formed either by the addition of an acid,- or by the juice of certain plants, or, as is the universal practice in this country, by the use of rennet, which is prepared from the fourth stomach of the young calf. Its peculiar action in coagulating the casein of milk is due to the presence in this stomach of minute cells contained in the gastrie juice, and the process is one of fermentation, rapidly effected by minute microscopic bodies, of which the liquid composing the steepings of rennets in full. Over 1000 of them have been counted in one five-hun-dredth part of a drop taken from a gallon of water in which a single rennet has been soaked; hence, at this rate, a rennet would contain 200,000 millions of them. It is claimed that this active agency in rennet may be multiplied and carried from one lot to another of milk, the same as leaven in bread-making, and hence rennet is really a true yeast. It is only the fourth or true digesting stomach ef the calf from which rennet can be prepared out of the inner lining or mucous membrane. They are usually in their best condition when the calf is from five to ten days old, but do not vary materially in strength while the young animal lives entirely on milk. As soon as the calves begin to live on solid food, the strength of their stomachs as rennets grow feeble. The calf should be perfectly healthy, must have suckled the cow four or five daj s, and to within a short time of killing. If it has been without food for any length of time, the stomach becomes inflamed and congested with blood, and especially so if the calf has been driven or carried much of a distance, since then it is of no value for rennet. The stomach should be taken out and well cleaned at once aft f r the calf is killed, by careful wiping with a moist cloth or sponge, or by rinsing, but in no case should water be poured upon it. As soon as cold, let it be lightly salted and left to dry on a dish for a day or two, then stretched on a hook or crooked stick, and hung up to dry in a place where the temperature is moderately warm. The Bavarian method is to blow up the rennet like a bladder, and tie one end to keep out air, first putting on it a little salt at the place where tied ; this skin, being thus made very thin, will dry rapidly and keep well. Sometimes they are suspended in paper bags. Rennets lose their strength if kept too warm, but they are much improved by alternate freezing and thawing if kept open to dry ak ; they should not be allowed to gather dampness, since their strength will evaporate if thus exposed. Their quality improves by at least one year’s age, and they part with the strong odour so common to green rennets. This prepared stomach or rennet, when steeped in water, produces a decoction which possesses the power of thickening milk or of decomposing it, and separating the casein from the liquid or whey. The most convenient way to prepare the rennet for use is to place the stomach in a stone or earthen jar containing a brine sufficiently strong to prevent it f-iom tainting, with not exceeding two quarts of cold water ; allow the whole to stand for five days; then strain and put it into bottles ; or the rennet may be soaked over night in warm water, and next morning the infusion may be poured into the milk. In from fifteen to sixty minutes the milk becomes coagulated, the casein separating in a thick mass. The rennet possesses the chemical property of producing lactic acid, by acting upon the sugar in the milk ; the acid unites with the soda in the milk, which holds the casein in solution, when the casein separates, forming the curd. Showing the wonderful power of this agency, by taking a single ounce of this membrane or rennet thoroughly washed and dried, and placing it into ISOOoz. of milk, heated to 120 deg. Fahr., complete coagulation of the whole quantity will shortly follow. Remove the rennet from the curd, again wash, dry and weigh it, and it will be found to have lost but one seventeenth part of its weight. Thus it may be proved that one part of the active matter of the stomach may coagulate about 30,000 parts of milk. It would be seen from these facts that but a small, comparatively small, amount of rennet would be required by our cheese factories ; but such is not the case. The desire to hurry cheese oft' to market in ten or twenty days from the hoop requires far more of the rennet than is absolutely necessary in the more moderate operations of private dairies in former days. The home supply from the millions of calves which are slaughtered in this country is wholly inadequate to meet the demand for rennets, hence they are largely imported from Europe. It is to be hoped that the ! enterprising chemists and investigators of the nge will discover some method of extracting the active agent in rennet, and in a state of absolute purity and freedom from objectionable animal matter, with a degree of uniformity in strength as well as concentrated form. While American cheesemaking has made wonderful progress during the past twenty years, there yet remains a wide field for careful study and intelligent progress.— * * Scientific ”