770 THE POPULAR SCIENCE MONTHLY. 



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 gradu- 

 ally 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 ripen- 

 ing 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, how- 

 ever, these volatile substances permeate the butter and explain its 

 flavor. Of course, it is highly essential that only the proper de- 

 composition 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 disagree- 

 able 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 bac- 

 teria are concerned, for they cease to grow when the butter is 

 made. 



But why should they cease to grow ? Why do they not con- 

 tinue to cause the decomposition in the butter ? What becomes 



