Fermentations of Milk. 97 



them. The arrangement of the whey vat is often such 

 that it cannot be completely emptied and cleaned; the 

 sour whey thus presents favorable conditions for the 

 growth of the lactose-fermenting yeasts. The return of 

 the whey to the farm in the milk can that is often im- 

 perfectly cleaned may serve to contaminate the milk 

 with the yeast. In the making of Swiss cheese the whey 

 is often so handled as to favor especially the growth of 

 such yeasts, and since this type of cheese is prepared 

 from sweet milk, the competition between the yeast and 

 the acid-forming bacteria is not so sharp as in the mak- 

 ing of cheddar cheese. The writers have found several 



instances where considerable loss was occasioned in the 



% 



Swiss cheese industry through the development of gassy 

 cheese due to this type of fermentation. 



The yeasty or alcoholic fermentation may also be of 

 'importance in butter making. In many sections of the 

 country the milk is separated on the farm and the cream 

 is forwarded to the creamery at more or less infrequent 

 intervals. It becomes sour and if it has become contam- 

 inated with yeasts, they will find favorable conditions for 

 growth in the acid medium. A large amount of carbon 

 dioxide gas is produced. Cans of gathered cream often 

 foam to such an extent as to run over, and in some cases 

 actual explosions have occurred on account of the great 

 pressure caused by the gas. 



Bitter fermentation of milk. Bitterness in milk may 

 be due to bacteria that enter the milk after it is drawn 

 from the cow, or it may be caused by the feed consumed 

 by the animal. It has been previously shown that cer- 

 tain specific substances contained in the food may be 

 absorbed and reappear in the milk. If the animal eats 



