The conditions most favourable for the exclusive development of these organisms have been learnt by long practice; but should these conditions at any time fail to be observed, some other ferment, incapable of producing the particular kind of ripening wished for, may intrude itself. The chamber is then said to be “sick,” and has sometimes to be temporarily abandoned.
Special members of the yeast and mould families are also largely concerned in the ripening of certain cheeses, and their action is very similar to that mentioned above. Roquefort and Pontgibaud cheeses, for example, are ripened by Penicillium glaucum, or, in other words, bread mould. These cheeses are kept as near as possible to 32° F., not because so low a temperature is most favourable to the development of the mould, but because other ferments, and especially such as give rise to putrefaction (vibrios), are thereby checked. From the low temperature and unsuitable soil the ripening is apt to proceed so slowly that it is customary to expedite the fermentation by a liberal inoculation of mouldy bread, and by piercing holes to enable the plant to penetrate inwards.
In Gruyère cheese are found long cells constricted in the middle like an elongated figure of 8. These cells multiply by splitting in two at the constricted part, forming two individuals. A gelatinous layer surrounds each cell when young, and also divides and envelopes the new individuals. This, however, disappears with age, leaving the cell naked. The action of this organism is to resolve any milk sugar that may be present into alcohol, acetic acid, and carbonic acid, and as this latter is a gas, it forms a number of small bubbles in the cheese. Gruyère is a cooked cheese; for in order to hasten the elimination of the whey, and enable the curd to be pressed in the mould as quickly as possible, the curd is heated slowly, and with constant stirring, to about 120° F. This requires considerable care, for if the heating be too rapid, the grains formed are large, and in the press flatten out and adhere to one another, and so clothe the cheese with an impenetrable layer, through which the whey is unable to escape. On the other hand, an undercooked curd is liable to retain an excess of whey; and the evil of this is that too much gas is given off by the fermentation of the sugar, and consequently, instead of bubbles, long channels appear in the cheese, which depreciate the value of the product. Again, as the ferment is killed at a temperature very near 120° F. (varying a little with the acidity or alkalinity of the curd), it is very possible to destroy it by overheating, and then the cheese becomes dry, is difficult to mature, and is said to be “dead.” Under any circumstances the ripening of Gruyère cheese is a very slow process.
In Duclaux’s own district of Cantal, a soft, quickly maturing, uncooked cheese is made, which has the disadvantage of slowly depreciating after ripening, owing to the large quantity of moisture it contains. The practice is to curdle the milk rapidly, and then, while the curd still retains a considerable amount of whey, to allow it to ferment till all the milk sugar has disappeared. On pressing the mass, there is squeezed out a certain amount of liquid and much ferment; but the remainder, equivalent to half the weight of the cheese, is retained, owing to a curious change in the properties of the curd. So obstinately is this held, that, with additional pressure, fat is forced out in preference to water. Duclaux finds, however, that with cheese containing less fat—say, half skimmed and half raw milk—more liquid can be extracted, and thus a better-keeping cheese obtained. As the flavour and odour are derived almost entirely from the alteration products of the casein, the main characteristics of the Cantal cheese are not altered by this modification, and he consequently recommends its adoption.
The most praiseworthy part of Duclaux’s investigations—that on the life history of these organisms, and the isolation and investigation of the diastases secreted by them—is of too scientific a nature to be reproduced here. We may mention, however, that Manelli and Mussi, in their researches on the maturing of Parmesan cheese, have independently come to much the same conclusion as those given above; so there is every reason to consider that we possess now a correct explanation of the phenomena of cheese ripening.
Apart from the interest attached to the explanation of an every-day process, researches such as these are sure in the end to lead to results of direct practical utility. Little by little we are getting to understand that no process of fermentation or putrefaction can be truly called “spontaneous.” They are as much the result of sowing as a thistle that turns up in a field where it was not purposely planted; and just as we can keep our agricultural crops in order by due attention, so crops of ferments can be controlled, the valuable ones being cultivated, and the pernicious weeds sterilised. Methods are known to the vinegar maker by which he can rear, when he needs it, unmixed crops of Mycoderma aceti to ferment his liquors; and the high-class brewer already uses the microscope to ascertain the healthiness of his yeast plant and its freedom from bacteria. May not even cheesemaking, then, be raised from an empirical art into a science, and each cheese factory of the future devote itself knowingly to the cultivation of its own appropriate fungus, learning its likes and its dislikes, and the enemies that have to be contended with? Even the mould sowing of the Roquefort peasants might be improved upon, and pure crops of ferment be raised to inoculate our cheeses. Granted that even then our finest cheeses would not be made better, yet the possibility of raising all cheese to the highest standard of quality of which it is capable is surely sufficient to claim for the scientific experimenter respect and encouragement.
In France there are a variety of cheeses which vary in consistence, constitution, flavour, and ability to keep, and these differences are rather owing to the process of manufacture than to the nature of the soil or the peculiarity of climate. The various denominations applied to them, too, indicate differences in manipulation rather than any change in their matter. Nevertheless, we are far from partaking of the opinion of those who deny that both sun and soil have any influence; for as with wine and cider, so with butter and cheese, the pasture has a marked action upon aroma and quality. If we consider the general manner or process of manufacture, we find that it comprehends five distinct operations, which in France are called: 1st, coagulation du lait, or the formation of the curd; 2nd, rompage, or breaking up of the curd; 3rd, égouttage, or drainage, which is accompanied in some cases by pressage or pressing; 4th, salaison, or salting; and 5th, fermentation, or maturing of the cheese. It is in the various methods, many of which differ very little from each other, and in all of which these operations are in force, but carried out under different conditions, that it is found possible to make 40 or more varieties of cheese, which are divided into 4 categories; 1st, fresh soft cheese; 2nd, salt ditto ditto; 3rd, firm or medium-pressed ditto; 4th, cured cheese, more or less hard and pressed.
In the first category we have the Neufchâtel, the manufacture of which is extensive and profitable in the district of Bray; the Brie, the Pont l’Evêque, and the Camembert may be mentioned as examples of the second; Roquefort and Dutch of the third; and Gruyère and Parmesan of the fourth.
There are defects to which even the best cheeses are commonly subject—defects, of the causes of which the professed cheese-makers themselves do not always give consistent accounts. Every good cheese should be of uniformly smooth surface, and perfectly firm; of colour unvarying throughout the whole surface, save only where the marks of age, necessary to certain kinds, appear. Softness and soapiness of texture; cracks, attributed by some to the action of lime on pasture, by others to the employment of too strong a draught in the process of drying; and holes, caused by “heaving” or “sweating,” are patent signs of imperfection which should warn the most careless purchaser against the cheese in which any of them are found. “Marbling,” the worst of all faults, is a mottled appearance of the surface, somewhat resembling the veining of marble. It is due to one or more of the following causes: not properly scalding the cheese; adding the colouring (which should be put in before the rennet) after the cheese has come; not properly squeezing out the whey. Wherever this occurs, it imparts to the cheese an exceeding ill flavour—in fact, makes it unfit to be eaten. It is especially dangerous in cheeses of the North Wilts kind, where the surface is invisible to the purchaser. Rankness of flavour, which can of course be guarded against by those who buy their own cheese, is also to be met with in the best kinds. This has been imputed to impurity of rennet; but, as it is frequently found in the cheeses of Scotland, where it is pretended that the greatest care is taken of the rennet, it may possibly also result from bad quality of pasture. In the Scotch dairy farms it is said to be obviated by pouring a very small quantity of saltpetre into the pail before milking the cows.