RELATION OF BACTERIA TO DAIRY INDUSTRY. 83 



has found to be advantageous for the purpose of 

 cream ripening (Figs. 21-23). 



There have hitherto appeared a number of 

 difficulties in the way of reaching complete suc- 

 cess in these directions. The most prominent 

 arises in devising a method of 

 using pure cultures in the 

 creamery. The cream which 

 the butter makers desire to 

 ripen is, as we have seen, al- 

 ready impregnated with bac- 

 teria, and would ripen in a 

 fashion of its own even if no 

 pure culture of bacteria were FlG - 23. Dairy bacteri- 

 added thereto. Pure cultures ^fSSSfMS!: 

 can not therefore be used as 

 simply as can yeast in bread dough. It is plain 

 that the simple addition of a pure culture to a mass 

 of cream would not produce the desired effects, 

 because the cream would be ripened then, not by 

 the pure culture alone, but by the pure culture 

 plus all of the bacteria that were originally pres- 

 ent. It would, of course, be something of a ques- 

 tion as to whether under these conditions the 

 results would be favourable, and it would seem 

 that this method would not furnish any means of 

 getting rid of bad tastes and flavours which have 

 come from the presence of malign species of bac- 

 teria. It is plainly desirable to get rid of the 

 cream bacteria before the pure culture is added. 

 This can be readily done by heating it to a tem- 

 perature of 69 C. (155 F.) for a short time, this 

 temperature being sufficient to destroy most of 

 the bacteria. The subsequent addition of the 

 pure culture of cream-ripening bacteria will cause 

 the cream to ripen under the influence of the add- 



