Page:Popular Science Monthly Volume 40.djvu/793

Rh of them after the churning? The answer to these questions is simple. Many of the bacteria go off in the buttermilk; many more are removed by the water used in washing, but many of them still remain in the butter. Here, however, their active life is nearly over, for the salt added to the butter checks their growth and their numbers begin to diminish. Butter is not a good medium for their development, and, after a few weeks, they practically disappear. Their growth in the butter is thus so slight that it is of no importance and ordinarily produces no noticeable result. To be sure, the butter may subsequently become rancid, and until recently it has been supposed that the rancidity of butter was due to bacteria growth. Some species of bacteria certainly produce butyric acid, and this is one of the most prominent characteristics of rancid butter. But it has been recently shown that butter may become rancid independently of bacteria growth, the direct oxidizing power of the air producing the effect. Bacteria, it is true, may hasten the process, but they are probably not a necessary cause. After the butter is made, then, the bacteria are of no further importance, and unless there should chance to be some disease-germs among them nothing further will result from their action.

The butter-maker thus forces the bacteria to give to his butter a flavor for which he gets a good price in the market. Unfortunately for him, however, there is more than one species of bacteria which may readily get into his cream and produce its ripening, and not all of them are equally serviceable to him. Many species of bacteria give a very unpleasant flavor to the butter if they are abundant in the ripening cream. While they cut the slime that holds the fat-globules and thus make the churning easy, the aroma produced by different species is by no means always satisfactory. It has been found that many of the species which commonly grow in ripening cream will produce very disagreeable butter if they are allowed to act alone. Others acting alone produce good butter, and the latter must, of course, outweigh the former, or the butter will be unsatisfactory.

The fact is, that during the ripening of the cream a great battle is going on among the different species of bacteria. Some of them find the conditions of the ripening cream favorable to their growth, while others find it less favorable. The favored species multiply rapidly, and may largely crowd out of existence those less favored. Some species may chance to get the start of others by being in greater numbers at the outset, while another species will make up for all drawbacks by having a more rapid rate of multiplication. The final result of the struggle will depend upon an infinite variety of conditions, which will be entirely beyond our knowledge. The condition of the cow, the manner of