in the United States, asserts that there are digestive enzymes—that
is, unorganized or soluble ferments—inherent in the milk
itself that render the casein soluble. The supporters of the
bacterial theory are ranged in two classes. The one, led by
Duclaux, regards the breaking down of the casein as due to the
action of liquefying bacteria (Tyrothrix forms). On the other
hand, von Freudenreich has ascribed these changes to the lactic-acid
type of bacteria, which develop so luxuriantly in hard cheese
like Cheddar.
With regard to the American theory, and in view of the important practical results obtained by Babcock and Russell at the Wisconsin experiment station, the following account[1] of their work is of interest, especially as the subject is of high practical importance. In 1897 they announced the discovery of an inherent enzyme in milk, which they named galactase, and which has the power of digesting the casein of milk, and producing chemical decomposition products similar to those that normally occur in ripened cheese. The theory has been advanced by them that this enzyme is an important factor in the ripening changes; and as in their experiments bacterial action was excluded by the use of anaesthetic agents, they conclude that, so far as the breaking down of the casein is concerned, bacteria are not essential to this process. In formulating a theory of cheese-ripening, they have further pointed out the necessity of considering the action of rennet extract as a factor concerned in the curing changes. They have shown that the addition of increased quantities of rennet extract materially hastens the rate of ripening, and that this is due to the pepsin which is present in all commercial rennet extracts. They find it easily possible to differentiate between the proteolytic action—that is, the decomposing of proteids—of pepsin and galactase, in that the first-named enzyme is incapable of producing decomposition products lower than the peptones precipitated by tannin. They have shown that the increased solubility—the ripening changes—of the casein in cheese made with rennet is attributable solely to the products peculiar to peptic digestion. The addition of rennet extract or pepsin to fresh milk does not produce this change, unless the acidity of the milk is allowed to develop to a point which experience has shown to be the best adapted to the making of Cheddar cheese. The rationale of the empirical process of ripening the milk before the addition of the rennet is thus explained. In studying the properties of galactase it was further found that this enzyme, as well as those present in rennet extract, is operative at very low temperatures, even below freezing-point. When cheese made in the normal manner was kept at temperatures ranging from 25° to 45° F. for periods averaging from eight to eighteen months, it was found that the texture of the product simulated that of a perfectly ripened cheese, but that such cheese developed a very mild flavour in comparison with the normally-cured product. Subsequent storage at somewhat higher temperatures gives to such cheese a flavour the intensity of which is determined by the duration of storage. This indicates that the breaking down of the casein and the production of the flavour peculiar to cheese are in a way independent of each other, and may be independently controlled—a point of great economic importance in commercial practice. Although it is generally believed that cheese ripened at low temperatures is apt to develop a more or less bitter flavour, the flavours in the cases described were found to be practically perfect. Under these conditions of curing, bacterial activity is inoperative, and these experiments are held to furnish an independent proof of the enzyme theory.
Not only are these investigations of interest from the scientific standpoint, as throwing light on the obscure processes of cheese-curing, but from a practical point of view they open up a new field for commercial exploitation. The inability to control the temperature in the ordinary factory curing-room results in serious losses, on account of the poor and uneven quality of the product, and the consumption of cheese has been greatly lessened thereby. These conditions may all be avoided by this low-temperature curing process, and it is not improbable that the cheese industry may undergo important changes in methods of treatment. With the introduction of cold-storage curing, and the necessity of constructing centralized plant for this purpose, the cheese industry may perhaps come to be differentiated into the manufacture of the product in factories of relatively cheap construction, and the curing or ripening of the cheese in central curing stations. In this way not only would the losses which occur under present practices be obviated, but the improvement in the quality of the cured product would be more than sufficient to cover the cost of cold-storage curing.
The characteristics of typical specimens of the different kinds of English cheese may be briefly described. Cheddar cheese possesses the aroma and flavour of a nut—the so-called “nutty” flavour. It should melt in the mouth, and taste neither sweet nor acid. It is of flaky texture, neither hard nor crumbly, and is firm to the touch. It is early-ripening and, if not too much acid is developed in the making, long-keeping. Before all others it is a cosmopolitan cheese. Some cheeses are “plain,” that is, they possess the natural paleness of the curd, but many are coloured with annatto—a practice that might be dispensed with. The average weight of a Cheddar cheese is about 70 ℔. Stilton cheese is popularly but erroneously supposed to be commonly made from morning’s whole milk with evening’s cream added, and to be a “double-cream” cheese. The texture is waxy, and a blue-green mould permeates the mass if well ripened; the flavour is suggestive of decay. The average weight of a Stilton is 15 ℔. Cheshire cheese has a fairly firm and uniform texture, neither flaky on the one hand nor waxy on the other; is of somewhat sharp and piquant flavour when fully ripe; and is often—at eighteen months old, when a well-made Cheshire cheese is at its best—permeated with a blue-green mould, which, as in the case of Stilton cheese, contributes a characteristic flavour which is much appreciated. Cheshire cheese is, like Cheddar, sometimes highly-coloured, but the practice is quite unnecessary; the weight is about 55 ℔. Gloucester cheese has a firm, somewhat soapy, texture and sweet flavour. Double Gloucester differs from single Gloucester only in size, the former usually weighing 26 to 30 ℔, and the latter 13 to 15 ℔. Leicester cheese is somewhat loose in texture, and mellow and moist when nicely ripened. Its flavour is “clean,” sweet and mild, and its aroma pleasant. To those who prefer a mild flavour in cheese, a perfect Leicester is perhaps the most attractive of all the so-called “hard” cheese; the average weight of such a cheese is about 35 ℔. Derby cheese in its best forms is much like Leicester, being “clean” in flavour and mellow. It is sometimes rather flaky in texture, and is slow-ripening and long-keeping if made on the old lines; the average weight is 25 ℔. Lancashire cheese, when well made and ripe, is loose in texture and is mellow; it has a piquant flavour. As a rule it ripens early and does not keep long. Dorset cheese—sometimes called “blue vinny” (or veiny)—is of firm texture, blue-moulded, and rather sharp-flavoured when fully ripe; it has local popularity and the best makes are rather like Stilton. Wensleydale cheese, a local product in North Yorkshire, is of fairly firm texture and mild flavour, and may almost be spread with a knife when ripe; the finest makes are equal to the best Stilton. Cotherstone cheese, also a Yorkshire product, is very much like Stilton and commonly preferable to it. The blue-green mould develops, and the cheese is fairly mellow and moist, whereas many Stiltons are hard and dry. Wiltshire cheese, in the form of “Wilts truckles,” may be described as small Cheddars, the weight being usually about 16 ℔. Caerphilly cheese is a thin, flat product, having the appearance of an undersized single Gloucester and weighing about 8 ℔; it has no very marked characteristics, but enters largely into local consumption amongst the mining population of Glamorganshire and Monmouthshire. Soft cheese of various kinds is made in many localities, beyond which its reputation scarcely extends. One of the oldest and best, somewhat resembling Camembert when well ripened, is the little “Slipcote,” made on a small scale in the county of Rutland; it is a soft, mellow, moist cheese, its coat slipping off readily when the cheese is at its best for eating—hence the name. Cream cheese is likewise made in many districts, but nowhere to a great extent. A
- ↑ Experiment Station Record, xii. 9 (Washington, 1901).
