184 BACTERIA IN BUTTER AND OLEOMARGARINE. 
forming not more than i or 2 per cent, of the whole, but the per- 
centage rises rapidly. After several hours, the time varying with 
different specimens, the acid bacteria constitute a large proportion 
of the whole. From this time, after they form perhaps 50 per cent, 
of all the, bacteria present, the other species begin to be seriously 
affected by the acid produced. The acid-forming germs still con- 
tinue to increase in numbers, while the others cease to grow so 
rapidly, soon begin to diminish, and finally may largely or 
wholly disappear. The result of this is that, during the last stages 
of the ripening, there may be present in the cream nothing but acid 
bacteria, which sour the cream and produce the final changes in the 
ripening. 
Thus it will be seen that the ripening of cream may be divided 
into two stages. In the first the growth of the miscellaneous 
species of bacteria continues, and all types may become more or less 
abundant. In the second the acid-forming germs gradually force 
the others into the background and finally crowd them out entirely. 
Both of these stages doubtless contribute to the final product. 
Without the proper lactic organisms it is impossible to get the 
proper flavored butter. But butter made from pasteurized cream 
and ripened by pure cultures of lactic acid bacteria does not develop 
so much flavor as that in which the original bacteria are allowed 
to grow with the acid germs. Hence, it is probable that the develop- 
ment of the miscellaneous bacteria in the first phase of the ripening 
has not a little to do with the final butter flavors. 
The Effect of Different Species of Bacteria. The butter- 
maker thus needs bacteria, but he must have the right kind. When 
cream is collected for a large creamery from many sources there 
are sure to be in it quantities of different varieties of bacteria, each 
patron contributing his quota. Each species may be expected to 
have its effect upon the cream during the ripening, and the resulting 
butter will show this effect. Actual study has proved that different 
species of bacteria, when allowed to grow in the ripening cream, 
produce very different types of butter. Some produce bitter butter , 
others tainted butter, others insipid butter, and others a strong odor, 
almost like that of putrefaction. Some species produce a tallowy 
