66 Agricultural Bacteriology. 



and hold many substances having pronounced odors and 

 tastes. In the souring of cream, various products are 

 formed, some of which are absorbed by the butter fat, 

 and give to the sour-cream butter its peculiar flavor. 

 The lactic acid itself is of no importance as far as flavor 

 production is concerned. 



That the by-products of the lactic fermentation are the 

 important thing, and not any change in the fat during 

 the souring process can be shown by the fact that if 

 sweet cream is mixed with sour skim milk and churned at 

 once, the butter will have as much flavor as though the 

 cream itself had been allowed to sour. This fact is made 

 use of by renovated butter manufacturers and oleomarga- 

 rine makers to give taste and odor to the tasteless fats 

 they employ. 



Spontaneous ripening of cream. All lactic acid bac- 

 teria do not produce proper flavoring substances. Those 

 which break up the milk sugar with the formation of gas 

 in the milk frequently impart an undesirable flavor to 

 butter. Because of the fact that clean pure milk us- 

 ually undergoes a desirable type of fermentation, the so 

 called spontaneous or natural ripening of cream gener- 

 ally results in the production of a satisfactory product. 

 This is the method usually employed on farms and where 

 care is taken, the best quality of butter can often be pro- 

 duced. The farm product is not likely to be as constant 

 in quality as the factory butter. 



Home-made starters. With the advent of the mod- 

 ern creamery, it became possible to make a more uniform 

 product because conditions could be more closely con- 

 trolled. The most prominent factor in this is the churn- 

 ing at regular intervals. This should be done when a 



