CHAPTER XXIII. 



THE ARTIFICIAL SOURING OF CREAM. 



141. The Acid Generator. 



THE preferences exhibited by the various families of the human 

 race for different kinds of butter are very marked. China and 

 Japan, for instance to which countries Denmark ships large 

 quantities of this food-stuff prefer sweet-cream butter, i.e. that 

 prepared from fresh, sweet cream ; whereas, in Scandinavian coun- 

 tries, Denmark itself, North Germany, and England, a preference 

 for sour-cream butter prevails. 



In order to obtain the latter product, the cream is allowed to 

 turn sour and undergo a fermentation, principally of a lactic 

 character. Until within the last few years the general practice 

 was simply to leave the cream to become sour spontaneously; hence, 

 in view of the fluctuation to which the bacterial flora of milk and 

 cream is exposed, it is not surprising that such a method of pro- 

 cedure frequently resulted in the production of defective butter. 



A reliable means of combating this adverse tendency is, how- 

 ever, now available, namely, the process introduced into the 

 dairy industry in 1890 by H. WBIGMANN (III.-V.) of artificially 

 souring cream by the aid of pure cultures of selected races of 

 lactic acid bacteria. This process is divided into two manipula- 

 tions : the preparation of the acid generator and the preliminary 

 treatment of the cream to be soured. 



The acid generator (or starter) brings the cream quickly into 

 a state of fermentation. According to Weigmann's recipe, it is 

 prepared as follows : Separated or skimmed milk in the pro- 

 portion of 2-3 per cent, of the cream to be acidified is warmed 

 up to about 60 C. and then immediately re-cooled as quickly and 

 as much as possible. This treatment kills some of the bacteria in 

 the milk and weakens others to such an extent that they cannot 

 offer more than a feeble opposition to the development of the 

 lactic acid bacteria, which are then added to the treated skim- 

 milk. For this purpose a pure culture of lactic ferment, obtained 

 from a Dairy Experimental Station, is employed. The vessel is 

 kept for twenty-four hours at a medium temperature (15 C.), by 

 which time its contents will be converted into acid generator 

 ready for use. 



The cream, also, requires a preliminary treatment to prepare 



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