Page:Popular Science Monthly Volume 58.djvu/157

Rh value whatever. Incidentally, it is true that the cheese also furnishes a considerable amount of food material. Thus it nourishes as well as stimulates and delights; but, after all, we must recognize that its chief value is in its flavor rather than in its nutritive quality.

Hence it becomes a very significant question to inquire into the source of this flavor. We find, first, that the cheese as originally made possesses no flavor, or, at least, none of that peculiar flavor which we know as cheesy. Cheese is made from milk by causing the casein in the milk to be precipitated, i. e., causing the milk to curdle, commonly by the addition of rennet, or, in so-called Dutch cheeses, by simply allowing the milk to sour. The precipitated casein is then separated from the liquids of the milk, and the curd, when subsequently pressed and molded, becomes the cheese. But the freshly-made cheese possesses no flavor, nor does the flavor develop to any degree until after it has passed through a process known as 'ripening.' The ripening of cheese may take several days or several months, or, in some cases, one or two years; but the flavor always arises during this process. Moreover, the various cheeses with their varieties of flavors are mostly made from the same kind of milk, but are subjected to different modes of ripening, and the distinctive quality in the endless types of cheeses is due in large measure to differences in the method of bringing about this ripening. Clearly enough the flavor is a product of cheese ripening, and if we wish to find the source of these most valuable flavors we must seek it in the ripening process.

This cheese ripening proves to be a two-fold process. The first change in the cheese is a chemical one, which results in altering the chemical nature of the cheese in such a way as to render it more easy of digestion. This change appears to be due in part to a certain ferment which is found in milk. This material belongs to the class of chemical ferments or enzymes and is a normal constituent of milk, although its presence was not mistrusted until recently pointed out by two American investigators. With the chemical changes produced by this enzyme we are not here particularly concerned. It is certainly not the cause of all the flavors which develop in the cheeses, and, therefore, this character of the ripened cheese must be chiefly attributed to another factor. There is no doubt that this other factor is a living one. The flavors can generally be traced directly to the growth upon and within the cheese of a variety of plants; and the ripening is carried on in a fashion designed, at the same time, to stimulate the growth of some species of plants and to check the growth of others.

Cheeses are of two kinds, hard and soft. As implied in the name, there is a difference in the consistency of the cheese. But this is not all; for on account of the methods of manufacturing, the ripening is produced by different classes of plants in the two classes of cheeses.