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

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

If the cream is allowed to undergo the acid fermentation before churning, the butter has a much higher degree of flavor and one that differs materially in kind. Under primitive methods, it was difficult to keep the cream sweet until it could be churned. On the small farm with gravity creaming in shallow vessels and infrequent churning, the cream was certain to be sour when churned. Undoubtedly, the making of butter from sour cream came into use because of its greater convenience; people became accustomed to sour-cream butter, and at the present time it is used in the greater part of the world, and is the type made in all of the great dairy countries.

Ripening of cream. In modern dairy practice the souring of the cream is called the ripening process, and is, where the best methods are employed, largely under the control of the butter maker. The changes that go on in the ripening process are the same as have been discussed in the acid fermentation of milk. The increase in acid is accompanied by an enormous increase in the number of bacteria; the ripe cream will contain hundreds of millions of bacteria in each cubic centimeter. The effect of this germ life is to improve or injure the butter, depending upon the class of bacteria to which it belongs. The problem of the modern butter maker is to control the kinds of bacteria growing in the cream.

The temperature at which cream is held during the ripening process is favorable to the growth of the acid-forming bacteria; hence, in ripe cream, they are practically the only kind of bacteria to be found. It must be remembered however, that there are different classes of acid-forming organisms, some of which produce desirable flavors, while others are distinctly harmful.

The intensity of flavor of butter is, in a general way, directly related to the amount of acid that is formed in the cream. A low acidity at time of churning is usually associated with a mild flavor, while a higher degree of acidity, up to a certain point, imparts a more pronounced flavor to the product. If cream is over-ripened, the quality of the flavor is seriously impaired.

In determining the acidity of cream, a definite volume is taken, and the acidity determined by titration, expressing the results as such a per cent of lactic acid. Manifestly, the amount of fat in the cream influences the apparent per cent of acidity. The acidity will not usually exceed 0.5 to 0.7 per cent, but in reality the serum will contain more than this, as the acid is formed in the serum, the butter fat having no role whatever. In a very rich cream, 40 to 50 per cent fat, it is impossible to develop more than 0.4 to 0.5 per cent of acidity, and the flavor of the butter will be low, because of the relation between the amount of acid and fat, while in a thin cream having the same acidity, the ratio between the amounts of fat and acid will be very different. For example, in one hundred pounds of 50 per cent cream of 0.5 per cent acidity there will be one-half pound of acid and fifty pounds of fat; in the same quantity of cream containing 20 per cent of fat and having an acidity of 0.5 per cent there will be one-half pound of acid to twenty pounds of fat. The flavor of the butter from the rich cream will be quite different in intensity from that made from the thinner cream.

The acidity of cream cannot be determined with any degree of accuracy by the taste or odor. Every butter maker should have some method of determining the degree of acidity in his cream, so that he may better control the flavor of his product. Several methods have been devised for this purpose and the necessary apparatus is sold by all dairy supply houses.

The effect of the ripening of the cream is shown not only in the flavor of the product, but in a number of other ways. Sour cream churns more easily, and more exhaustively than does sweet cream. It is supposed that the fat globules are surrounded by a film of albuminous material which prevents their coalescing readily. During the ripening process, the action of the acid apparently dissolves this enveloping substance, and the globules cohere more easily in the churning process.

When raw cream is used the ripened-cream butter keeps better than that made from sweet cream. In sweet cream there are few lactic bacteria, the majority of the bacteria present being of various kinds, many of which may be injurious, so far as the keeping quality is concerned. In sour-cream butter the lactic bacteria make up over 99 per cent of the bacteria present, and their presence tends to prevent the development of undesirable non-acid forms.