Bacteriologists have been able to explain with a considerable degree of accuracy the object of this ripening.  The process is really a fermentation comparable to the fermentation that takes place in a brewer’s malt.  The growth of bacteria during the ripening produces chemical changes of a somewhat complicated character, and concerns each of the ingredients of the milk.  The lactic-acid organisms affect the milk sugar and produce lactic acid; others act upon the fat, producing slight changes therein; while others act upon the casein and the albumens of the milk.  As a result, various biproducts of decomposition arise, and it is these biproducts of decomposition that make the difference between the ripened and the unripened cream.  They render it sour and curdle it, and they also produce the flavours and aromas that characterize it.  Products of decomposition are generally looked upon as undesirable for food, and this is equally true of these products that arise in cream if the decomposition is allowed to continue long enough.  If the ripening, instead of being stopped at the end of a day or two, is allowed to continue several days, the cream becomes decayed and the butter made therefrom is decidedly offensive.  But under the conditions of ordinary ripening, when the process is stopped at the right moment, the decomposition products are pleasant rather than unpleasant, and the flavours and aromas which they impart to the cream and to the subsequent butter are those that are desired.  It is these decomposition products that give the peculiar character to a high quality of butter, and this peculiar quality is a matter that determines the price which the butter maker can obtain for his product.

But, unfortunately, the butter maker is not always able to depend upon the ripening.  While commonly it progresses in a satisfactory manner, sometimes, for no reason that he can assign, the ripening does not progress normally.  Instead of developing the pleasant aroma and flavour of the properly ripened cream, the cream develops unpleasant tastes.  It may be bitter or somewhat tainted, and just as sure as these flavours develop in the cream, so sure does the quality of the butter suffer.  Moreover, it has been learned by experience that some creameries are incapable of obtaining an equally good ripening of their cream.  While some of them will obtain favourable results, others, with equal care, will obtain a far less favourable flavour and aroma in their butter.  The reason for all this has been explained by modern bacteriology.  In the milk, and consequently in the cream, there are always found many bacteria, but these are not always of the same kinds.  There are scores, and probably hundreds, of species of bacteria common in and around our barns and dairies, and the bacteria that are abundant and that grow in different lots of cream will not be always the same.  It makes a decided difference in the character of the ripening, and in the consequent flavours and aromas,