8O PRACTICAL DAIRY BACTERIOLOGY 



At 80 to 100. If the milk is kept at temperatures from 80 

 to 100, the results are far more variable. The bacteria grow 

 very much more rapidly, but we cannot tell so surely what 

 species will develop in greatest abundance so as to become pre- 

 dominant. In some cases here also the Bact. lactis acidi assumes 

 predominance and sours the milk; but in a great many other 

 cases, apparently the majority, some of the other types assume the 

 upper hand in milk. It frequently happens that at these higher 

 temperatures the gas-producing bacteria, Bact. aero genes, be- 

 come especially abundant, and by the time the milk has soured 

 it will contain large proportions of these organisms that are so 

 mischievous in various dairy products. 



For this reason it is extremely important that milk to be 

 used for butter-making, and especially for cheese-making, 

 should be kept at temperatures below 80, and after the curd- 

 ling by rennet should be cooled to below 80. The presence of 

 the gas-producing organisms is sure to produce mischief, whereas 

 the proper growth of the other lactic bacteria is a necessary 

 accompaniment to a good butter or cheese. From the facts 

 here outlined it is evident that dairymen should endeavor to get 

 milk quickly to a temperature below 70 in order to stimulate 

 the development of the proper lactic acid bacteria. It should 

 be remembered, however, that if the starter of the proper or- 

 ganisms be added to milk or cream so that this organism is 

 present in special abundance, a higher temperature of 80 may 

 frequently be safely used to hasten the souring of the milk. 

 Under these circumstances, since the desirable organisms are 

 added in great abundance, they succeed in producing their 

 action on milk in spite of gas-producing organisms or other 

 bacteria that may be present in smaller quantities. If, however, 

 ordinary milk or cream, without a starter, be ripened at a tem- 

 perature of 80, or thereabouts, the results will be very un- 

 certain, and in some cases gas production will give rise to 

 trouble and serious loss. 



