408 Bacteria in Relation to Country Life 



allowed to turn sour naturally. Separator skim-milk 

 may be used instead of whole milk or partly skimmed 

 milk. The following steps are much like those noted in 

 connection with the building up of pure-culture starters. 

 It is not necessary to build up a new starter for each 

 churning, for a quantity of ripened cream or of butter- 

 milk reserved from the preceding lot may be used for 

 the preparation of the starter. From time to time, 

 however, the building up of a new starter becomes 

 essential. 



Pure-culture starters possess certain advantages 

 which render their use acceptable to the butter-maker. 

 Experience soon teaches him how to control his ripening 

 process within narrow time limits, and he can, there- 

 fore, carry on his work with a precision not attainable 

 in the use of natural starters. He is more certain of 

 uniformity in his product, and finds himself, therefore, 

 able to place a standard article on the market. 



The natural starters, on the other hand, cannot always 

 be relied on. In spite of the care observed in their 

 preparation, they are apt, at times, to yield an unsatis- 

 factory product, both as to flavor and keeping quality. 

 With that much admitted, however, the skilled butter- 

 maker who uses natural starters believes that he can, 

 with their aid, produce a better-flavored product than 

 he could with the use of pure-culture starters. This is 

 not difficult to understand, since no single species has 

 yet been discovered that is capable of producing all of 

 the substances found in properly ripened and highly 

 flavored cream. According to Grotenfelt, Jensen char- 

 acterizes the ideal lactic-acid bacterium as possessing 



