106 DAIRY BACTERIOLOGY 



Yoghurt, acts favourably by simple reason of its large content of 

 lactic acid. 



As a third group of milk products may be mentioned Sparkling 

 Whey, and Whey Champagne, in which alcoholic fermentation is 

 very pronounced. In the Carpathians, sparkling whey made 

 from sheep's milk (Urda and Slcuta) is a favourite beverage, and 

 in Chile whey champagne is made by the fermentation of whey 

 with the addition of various saccharine and aromatic substances. 



In addition to its applications in the preparation of these 

 national milk products, the lactic acid fermentation plays an 

 important part in butter making from soured cream and in the 

 manufacture of margarine from soured skim milk. Its application 

 in the manufacture of lactic acid has already been touched upon 

 (see p. 31). The souring of cream will now occupy our special 

 attention. 



THE SOURING OF CREAM 



Like most practical discoveries, the souring of cream for butter 

 making owes its origin more or less to chance. In order to avoid 

 churning every day, it became the custom on small farms to save 

 the cream for several days and sometimes even for a whole week, 

 the different batches being mixed together, and naturally the cream 

 became sour. In many cases it was sour before mixing, as the 

 milk was often kept in a warm place for the cream to rise. In 

 the same way, the 'custom of churning sour cream ("gathered 

 cream ") naturally arose in the American creameries where 

 fresh cream is not available. Originally the butter prepared from 

 soured cream was extremely bad, but experience soon showed 

 how the worst defects might be avoided, and it was found that 

 under certain circumstances a particular aroma would be imparted 

 to the butter, which could not be produced with unripened cream, 

 and was appreciated by those who had acquired the taste for it. 

 Further, the use of ripened cream results in an increased yield of 

 butter as the fat globules coalesce more readily during churning 

 when the casein has been precipitated. Finally, the butter made 

 from ripened cream keeps better than that from unripened cream . 

 For these reasons the practice of souring cream was continued 

 when the dairies became so large that churning became a daily 

 operation. Even in Central Europe, where butter was generally 

 churned from fresh cream, it has become the custom to use soured, 

 or at any rate slightly soured, cream. The only difference between 

 " sweet " and " sour " butter will soon be that the former is 

 usually not salted. 



As the self-souring of cream is the oldest process, we may first 

 deal briefly with the changes which it involves. An actual 



