Outlines of dairy bacteriology, 10th edition / A concise manual for the use of students in dairying

by H. L. Russell; E. G. Hastings

Types of cheese. Cheese consists of the fat and the precipitated casein of milk, together with a large amount of water and the salts found in milk. The numerous types of cheese may be divided into two groups, depending on the manner in which the curdling of the milk is brought about. Sour-milk cheese is made from curd, formed as a result of the acid fermentation of the milk. Thus, at the very first stage in the making of this type, the importance of bacteria is apparent.

The second type is that made from curd, which is precipitated by the addition of rennet to the milk. This type may also be divided into two groups, depending upon their texture; the hard cheese, and the soft cheese. The ordinary cheddar, the common American type, is the most important example of the hard cheese; Limburger, of the soft cheese. Cheese are designated as hard or soft, depending upon the amount of whey that is retained in them during the making process. The moisture content has an important influence on the type and amount of life that develops on and in the curd mass, and as will be seen, the ripening and flavor of the cheese are dependent upon these biological factors.

The two groups of hard and soft cheese have no sharply defined limits, but merge into each other. The extreme types of the hard cheese are so dry and firm that they can be cut only with difficulty. Such cheese are used primarily as condiments to impart a flavor to certain dishes, as macaroni, and for this purpose are grated. The extreme type of soft cheese is a soft, pasty mass and can be easily spread with a knife.

Hard cheese, because the ripening process goes on uniformly throughout the entire mass of cheese, may be made of any size which permits of commercial handling. They can also be kept for long periods and preserve their good qualities. Soft cheese are made in small sizes, since on account of their consistency, they could not otherwise be handled, and also because of the manner of ripening. The ripening is due to the action of organisms developing on the surface, the by-products of which diffuse into the curd. If the cheese are too large, the outer layers become overripe, while the interior remains more or less unchanged, or insufficiently changed. Soft cheese mature much more rapidly than hard cheese; consequently they are short lived.

Although made from the same substance, milk, it is noteworthy that there are over four hundred varieties of cheese produced. Most of these find only a local market where made. Less than a dozen varieties are to be regarded as general articles of commerce.

Quality of milk. In the making of butter there are a number of processes that the maker can use when he finds himself obliged to utilize poor milk. The milk can be pasteurized and the harmful bacteria thus destroyed; desirable kinds can then be added in the form of a pure-culture starter. Pasteurization also drives off some of the volatile by-products of the first acid fermentation. By the use of these means, the maker can prepare a very good product from poor material.

In the making of most kinds of cheese, especially those of the greatest commercial importance, the cheese maker can call to his help no such aids, but must use the milk as it is brought to him. It is possible to prepare certain kinds of soft cheese from pasteurized milk that differ in no essential point from the same cheese made from raw milk. Hard cheese are also made from pasteurized milk, but in most cases such cheese differ, especially in the degree of flavor, from that made from unheated milk. It is quite probable that, as the factors concerned in the ripening of cheese become better known, methods will be evolved for the successful production of many kinds of cheese from pasteurized milk.

It has been shown that the quality of milk is almost wholly dependent upon the number and kinds of bacteria it contains. These bacteria pass into the cheese, and there produce the same products as they would have done in the milk itself. In butter making, practically all processes are under the control of the maker, until the product is ready for the market; but cheese, on the other hand, passes through a complicated series of changes after it has left the maker's control. During the manipulation of the milk and the curd in the vat, he can exert some influence on the quality of the product, but he is much more dependent on the quality of the milk than is the case in butter making.

Every effort should therefore be made to furnish to the cheese maker the quality of milk from which he can prepare fine cheese. In other words, the milk should be produced under clean conditions and carefully cooled and handled until delivered to the maker. Poor milk from a single farm may have such an effect upon the cheese made from the milk of twenty farms as to depreciate the selling value of the entire product several cents per pound.