Page:Popular Science Monthly Volume 40.djvu/792

770 the large masses necessary for their separation from the liquid. It requires a deal of shaking to accomplish it when the slime is intact, and sweet cream may sometimes be churned for hours without producing the butter. But the ripening prepares the way for the churning. The acid formed by the bacteria gradually dissolves this slime, which is of an albuminous nature, and after it is thus dissolved the difficulty of the fusion is gone and a short shaking in the churn finishes the process. It is plain, too, that a larger amount of butter will be obtained from the cream, for in churning sweet cream much of the fat will be left behind in the form of small drops not to be separated from the slime even after the most vigorous churning.

As mentioned above, the second advantage derived from ripening is the development of the aroma of a first-class butter. Sweet-cream butter is tasteless, and the cause of the butter aroma is to be found in the decomposition products of bacteria growth. While growing in the cream they are splitting up the sugars and albuminoids present and producing decomposition products. Among them are many volatile products which have a prominent odor and taste, and these, as we have seen, produce the odor and taste of ripened cream. Now, of course, the butter obtained from such cream will be affected by these compounds, and thus we see that the delicate aroma of first-class butter is produced by the decomposition products of bacteria growth in the cream. These are volatile, and eventually pass away from the butter in large measure. It is well known that the delicate butter aroma is found only in fresh butter. Old butter is strong enough in its taste, but the peculiar delicate aroma is gone. When first made, however, these volatile substances permeate the butter and explain its flavor. Of course, it is highly essential that only the proper decomposition products should be developed, and for this reason it is a matter of high importance that the ripening shall be stopped at just the right time. If it is not continued long enough, the proper decomposition will not take place; and, on the other hand, if it is continued too long, the volatile products will approach those of putrefaction and give a strong-tasting butter. At just the right moment they are present in sufficient amount to give the butter a pleasant flavor without being so abundant as to give a disagreeable one. The experience of the butter-maker guides him in determining when to stop the bacteria growth, and here is one of the points of skill in butter-making. When the cream is ripe enough he churns it, and this ends the process, so far as the bacteria are concerned, for they cease to grow when the butter is made.

But why should they cease to grow? Why do they not continue to cause the decomposition in the butter? What becomes