46 CREAMERY BUTTER MAKING 



Most of the curdling and digesting bacteria are spore 

 bearing and can thus withstand unfavorable conditions 

 better than the lactic acid bacteria. For this reason milk- 

 that has been heated sufficiently to kill the lactic acid 

 bacteria, will often undergo the undesirable changes 

 attributable to the digesting and curdling organisms.. 



3. BUTYRIC FERMENTATION. 



It was mentioned that many bacteria have the power 

 of producing lactic acid but that the true lactic acid fer- 

 mentation is probably caused by a single species. So it 

 is with the butyric acid bacteria. While a number of 

 different organisms are known to produce this acid, Conn 

 is of the opinion that the common butyric fermentation 

 of milk and cream is due to a single species belonging 

 to the anaerobic type. 



The butyric acid produced by these organisms is the 

 chief cause of rancid flavors in cream and butter. These 

 bacteria are widely distributed in nature, being particu- 

 larly abundant in filth. They are almost universally 

 present in milk, from which they are hard to eradicate 

 on account of their resistant spores. It is on account 

 of these spores and their ability to grow in the absence 

 of oxygen that the butyric fermentation is often found 

 in ordinary sterilized milk from which the air has been 

 excluded. 



This class of bacteria has great significance in cream 

 ripening and in the keeping quality of butter. In the 

 ripening of cream the desirable flavor develops with the 

 increase of acidity until the latter has reached .6%. When 

 the development of acid goes beyond this, the flavor is 

 no longer of the desirable kind but turns rancid as a 

 result of the development of the butyric fermentation. 



