that is, made up from the elemental substances, or they are mixtures or compounds. On the contrary a food like cheese or wine is not a mixture or compound but a natural product from materials which themselves are food products. Milk is the raw material of cheese as the must of the grape is of wine. Both milk and must are rich and nutritious foods. The changes which each undergoes are in many respects the same. The must of wine undergoes an alcoholic fermentation and the milk sugar of cheese is subjected to a lactic fermentation and its casein to a proteolytic change which materially alters its character.
Cheese products are a very important part of food materials of the dairy. The term cheese is applied to the solid product produced from milk by coagulation of the casein with rennet or lactic acid and subjecting the solid product thus produced to a process of fermentation and ripening by the addition of appropriate seed material, seasoning, and storage at convenient temperature for varying periods of time. In the precipitation of the casein of milk the fat particles become mechanically entangled and form a part of the precipitate. There is a certain quantity of other milk constituents incorporated in the form of water, milk sugar, and mineral matter in the precipitated mass. The greater part of the other bodies which the milk contains, consisting of the milk sugar and a considerable portion of the soluble mineral matter, are separated in the form of whey. The composition of fresh cheese is that of that part of the milk which is precipitated and which is entangled mechanically in the precipitated matter. The ripened cheese is changed in its chemical constituents mostly as the result of fermentative action upon its nitrogenous constituents, that is, the casein, albumin, etc., contained therein. The ferments tend to change the casein into a more soluble form of protein, while at the same time they develop a flavor and aroma in a way agreeable to the nostril and palate. Various forms of moulds and other organisms grow on and in cheeses which influence their palatability and character. The final product of the ripened cheese varies not only with the nature of the original material as determined by the milk itself but with the character of the preparation and the nature of the organisms and ferments which are active during the ripening period, and also with the time and temperature of storage.
Kinds of Cheese.—It is not necessary and perhaps it would be impossible to attempt an enumeration of all the various kinds of cheese which are offered on the market. The first classification of cheese depends upon the character of the milk used. The term "cheese" in this country naturally refers to a product made from cow's milk since that is the principal milk used in the United States for cheese making. The term is used in this manual in that sense and when there is no qualifying word employed it is always understood that the product in question is made from the cow's milk. This implies that the milk is at least a standard milk, that is, a whole milk, unskimmed and
