Page:Popular Science Monthly Volume 40.djvu/791

Rh "ripen" The cream in a creamery is placed in large vats, and then kept at a constant warm temperature for about twenty-four hours. The cream is stirred frequently during this time, and at the end of the ripening it is seen to have changed its character. It is somewhat acid in taste, is slightly thickened, and has a pleasantly sour odor, though one quite different from that of sour milk. The cream is now churned, and the butter is found to separate readily, the quantity is at its maximum, and the butter obtained has the proper butter aroma.

Bacteriological study of the last few years has shown that this "ripening" is nothing more than a breeding of bacteria on a large scale. There were many bacteria in the cream at the beginning, and the ripening has been conducted at just the temperature at which bacteria grow rapidly. The result is, that their multiplication is marvelously rapid, and the number of bacteria present in ripened cream is beyond comprehension and almost beyond calculation. Five millions in a drop would not be too high an estimate for some specimens.

Now, what are the bacteria doing in the cream during their twenty-four hours' growth? They can not multiply so rapidly without producing profound changes in the cream. So far as the butter-maker is concerned their action is twofold: 1. There is produced in the cream a considerable amount of lactic acid, together with small quantities of other acids. 2. Various decomposition processes are going on which fill the cream with decomposition products, and these give rise to the odor and taste of ripened cream.

To understand the effect that this ripening has upon the butter-making, we must first ask what happens to the cream during the churning. If we look at a drop of milk under the microscope, we find that the butter-fat is in the form of the most minute drops. So small are they that they can not be readily separated from the liquid part of the milk. In cream we simply have the great mass of these drops together, but still not at all fused, like a lot of snow-balls floating in water. In the churn, however, the cream is agitated until the drops are shaken together and made to fuse with each other. They now form masses of fat large enough to be removed from the liquid in which they float, and these masses form the butter. But, looking at the cream more closely, we find a mechanical difficulty in the way of their ready fusion. The fat-drops are not free to move at will, for they are bound together in groups by a sort of slimy substance. As we watch the cream with our microscope we see the fat-globules are not easily shaken together, for the slimy matter prevents their direct contact. This slimy substance must be broken down and the drops shaken into each other before the butter can form into