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 



