THE DAIRY.

New Zealand Mail, Issue 1249, 6 February 1896, Page 6

THE DAIRY.

SOME PRINCIPLES OF GHEEBEThe art of cheesemakiug rests fundamentally on the action of micro-organ-isms. In the first place, theie are the bacteria, which, as a general thing, begin to infect the milk soon after it is drawn from the cow, and subsequently these which incorporated with it in the rennet. The coagulation of milk in the process of cheesemaking is the evidence of things not seen, and these things are bacteiia. The active piin- ' ciple in rennet is a ferment, and the result is the coatudum, which we make into cheese. This particular ferment i is a secretion in the stomach of young ! animals of the order mammalia, and is j presumably indispensable to the digestion of milk. Corresponding, if not similar, ferments are found in the stomachs of various other animals, but none of these are employed in cheesemaking, save to a very limited extent. Juices from certain plants will also i coagulate milk, but these, too, are j equally valueless in the dairy. Milk, indeed, may be coagulated by a variety [ of ferments and acids, but rennet only I has been found to answer the purpose I in a satisfactory manner. The juices, | for instance, of fig and melon trees, of j the artichoke, Gf some kinds of thistles, and of the common butterwort { (Pinqvticula vulgaris) exercise in milk I an action similar to that of calves' j rennet, but cheese made with their j assistance is very different from that we \ are accustomed to. The action of J these ferments is. apparently similar to that of rennet in the coagulation ot milk, but it is cbviously not identical,, for the result is not by any means the same. We may take it for granted,, indeed, that no> other instrument will, ever displace und supersede rennet in cheesemaking. ORIGIN" OF JRENNET. In what way the property of rennet as an agent nix the manufacture of cheese was firsD discovered (here is no record to show - but its antiquity in this respect is,, of course, very great, and may well account for the obscurity in which it must remain. Probably, however, its artificial use was suggested by its rsntiiraJ one, viz., the curdling of milk in a calf's stomach in the process of digestion, and this would be seen when a calf was'killed and the contents of its stomach noted. Be this as it may, rennet has been used from time immemorial in cheesemaking, and will continue to be so used to the end of the chapter. The processes of digestion in the stomach and of coagulation in the cheese-kettle are identical up to a given point, though it is slower in the latter than in the former case, in consequence of a difference of some twenty degrees Fahr., viz., 78deg to 82deg in the kettle and 98deg in the stomach. At a given point in coagulation the process is arrested in cheesemaking, the whey is removed, the curd is pressed into a solid shape, and the action of the rennet proceeds very slowly until the cheese is ripe. It is only in the fourth stomach of the calf that the active principle, or ferment, of rennet is found to be available for cheesemaking purposes, and this stomach is preserved for the purpose, or a rennet liquid, ready for use at aixy time, is prepared from it. The stomach must, in order to be in its best condition, be that of a calf which has nor. had any other kind of food than milk. ; and consequently it happens that calves fed for veal provide us with the best rennets, especially when they are killed within a month '• of their birth. ! THE ACTION OF RENNET. The coagulating agent in rennet is recognised by bacteriologists as a chemical or unorganised ferment, and the class to which it is assigned are known as " Enzymes." The classification of these, and their constant separation from organised ferments, both vegetable and animal, and these from each other, is of comparatively j recent date, and marks, perhaps, the : beginning— say thirty years ago —of modern scientific and popular research in the domain of the dairy. In the gastric juices of a calf's stomach both rennet and pepsin are found, and both ; of these are digestive ferments of great i importance ; but whether both operate 1 in the coagulation of milk in cheese- j making does not appear to have been, I determined at present. Rennet ob- I

viouslv lias its origin in the wall-cells of the stomach, for when the stomachs are carefully cleaned, all the liquid being removed from them and antiseptics applied for preservation, the rennet is there when the skins have oeen macerated in water and the water, or brine, is mixed with the milk. Unorganised ferments, like rennet, are understood to be the products of true or organised ferments, and while thev are soluble in water their progenitors —the true ferments—are nob. These last— the organised ferments having to an unlimited extent the power and faculty of reproducing themselves, under favourable conditions, can effect an unlimited amount of fermentative work, but it does not appear that an unorganised ierment possesses either the faculty of reproduction or mult/plication or the p.rjiwer of doing unlimited fermentative work. Yet practical eheesemakers have fancied that rennet became more effective by keeping—a fancy merely, in all probability. The action of rennet is to set up in milk a fermentation which soon becomes manifest in what we know as curd. The process is generally completed, for cheesemaking purposes, in about fifty to sixty minutes, at a temperature of 80deg "Fahr. or 27deg Centigrade; and it is understood that pure rennet is able to coagulate quite one million times its own bulk of milk. In cheese making, however, the rennet is not pure, for it is very largely diluted with water or brine. Rennet is said to be independent of acids and of the sugar of milk in its process of coagulation of milk ; but when milk is spontaneously coagulated, the active agent is a true or organist*d and. living ferment —the lactic ferment—and this kind of fermentation depends on the milk-sugar, which it decomposes into lactic acid. In cheesemaking, therefore, the ferment employed is a chemical ferment, whereas in the natural souring of milk it is an organic ferment that is at \, v ork. A cheese made from a coaguluoa produced by an organic ferment ripens, 01 rather decomposes, from the outsit/e to the inside, -whereas a renneted cheese ripens throughout at the same tirnev The most favourable temperature for the action of rennet in milk is 80deg to 85deg Fahr., and a temperature of 140 deg destroys it. Its action in cheese is believe*! to be that of ripening or assisting to ripen, and the most favourable temperature for this appears to be 68deg to 70deg Fahr. That the rennet remains unimpaired in the solid form of milk known as cheese has been proved by inserting pieces of ripe old cheese into new milk, the result being coagulation as before ; and it is even said that the riper the cheese, within limits, the greater its power in coagulating milk, and from this it is assumed that the chemical ferment, increases in volume, or in strength, as the cheese ripens. Anyway, however, rennet is indispensable to cheesemaking and to the subsequent proper ripening of the cheese; at the same time it is assisted in both by one or more of organic ferments, some of which render valuable aid, whilst others do nothing but mischief. cheese fermentation; It has been stated that the coagulation of milk in cheesemaking and the

digestion of milk in a calf's stomach are largely identical, up to a given point; that point is the separation of the curd from the whey in the cheesekettle. When the coagulum is firm enough to break cleanly over the finger, and this ought to be in about an hour's time at 80deg Fahr., it is broken or cut into small pieces with the object of liberating the whey, and this is done not only to check the action of the rennet ferment, but also to arrest the action of the lactic ferment, whi.-h last is said to be entirely dependent on the milk-sugar. When the whey has been removed the progress of lactic fermentation is at once arrested, because very nearly all the milk-sugar has gone off in the whey. The action of the rennet continues at the same rate as before, so long as the temperature of the curd is maintained at about 80deg; but when the cheese is put into the press vat, and its temperature is reduced ten or twenty degrees, the notion of the rennet is retarded, and herein is it that the paraJiex between.... cheesemaking and digestion has reached a divergent point so far as speed is concerned. The process is completed in the stomach in fcur hours, but in the cheese it goes on slowly for months, and the finis may be postponed for years. In the cheese, as a matter of fact, rottenness represents the completion of the process, and, in some sorts of cheese, this state is a long time in coming. In a letter to a contemporary, close upon nine years ago, Archdeacon Denison said : "I have a piece of Cheddar cheese lying under a glass on my hall table. It was made 41 years ago. It is hard now, but it ia quite sweet." WHY CHEESE IS MADE. The object is to preserve the valuable constituents of milk for consumption at any time, and in a form which is convenient in all respects, either for use or transport. This is accomplished by removing the whey, which, with the milk-sugar, forms about ninety per cent, of the milk. The milk ia coagulated by means of rennet—that is to say, the caseine of the milk ia coagulated, and as this contains nearly all the butter fat, as well as other solids except the lactose or milk-sugar, the manufactured cheese represents the vahmble constituents of the milk in about ten per cent, of the bulk and weight Milk is preserved in other forms, bub they are less convenient, and cheese possesses an individuality of which it cannot be deprived. The variety in the sorts of cheese that are made in one country or another, or in all, is almost bewildering; but they are all made -with the primary object of preserving milk for leisurely consumption ; other objects are seen in the presentation of tempting qualities of every sort, but it unfortunately occurs that only relatively few persons can make these tempting qualities. The whirligig of time will, perhaps, bring it to pass that large establishments are better than small ones, not only for making but also for the marketing of chee3e. On.ce we shall have mastered the bacteria- problem, our way out of many current difficulties will be plain. Rut, meanwhile, it seems absurd that people should, take cartloads of cheeae twenty-five miles to a fair, aa neigh-

boiirs o£ mine did last week, with the chalice of bringing them back unsold, bVer that dreaiy length of macadam that stretches between this place and the sprightly town of Derby.—J. P. Sheldon in Farm, Field and Fireside.