Bacteria and Butter-Making. 145 



3. Keeping quality of product. Butter made from pas- 

 teurized cream to which a pure-culture starter has been 

 added will keep much better than the ordinary product, be- 

 cause the diversity of the bacterial flora is less and the milk 

 is therefore not so likely to contain those organisms that 

 produce an "off" condition. 



4. Elimination of taints. Many defective conditions in 

 butter are attributable to the growth of undesirable bacteria 

 in the cream that result in the formation of "off" flavors 

 and taints. If cream is pasteurized, thereby destroying these 

 organisms, then ripened with pure ferments, it is generally 

 possible to eliminate the abnormal conditions. 1 Taints 

 may also be present in cream due to direct absorption from 

 the cow or through exposure to foul odors. 2 Troubles of 

 this sort may thus be carried over to the butter. This is 

 particularly true in regions where leeks and wild onions 

 abound, as in some of the Atlantic States. The heating of 

 the cream tends to expel these volatile taints, so that a 

 fairly good article of butter can be made from what would 

 otherwise be a relatively worthless product. 



Characteristics desired in culture starters. Certain con- 

 ditions as the following are desirable in starters made from 

 pure cultures: 



1. Vigorous growth in milk at ordinary ripening tem- 

 peratures. 



2. Ability to form acid so as to facilitate churning and 

 increase the yield of butter. 



3. Able to produce a clean flavor and desirable aroma. 



4. Impart a good keeping quality to butter. 



i Milch Zeit., 1891, p. 122; 1894, p. 284; 1895, p. 56; 1896, p. 163. 

 8 McKay, Bull. 32, Iowa Expt. Stat, p. 477. 

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