CHAPTER XVII. 



INDUSTRIAL APPLICATIONS OF FERMENTATIVE 

 PROCESSES (Continued]. 



1. BUTTER. 



As is well known, butter is made by the churning of cream. A few 

 countries, e.g. China and Japan, prefer sweet-cream butter, i.e. butter 

 made from fresh cream which has not lost its sweet taste ; but most 

 other nations prefer sour-cream butter, i.e. butter made from c^eam 

 which has been set aside and allowed to become sour. The process by 

 which cream becomes sour is called ripening, and it is in the manipula- 

 tion of the ripening that dairy bacteriologists have within the last few 

 years achieved such excellent results. As cream is an ideal food for 

 bacteria, it contains many thousands of bacteria per cubic centimetre, 

 and when set aside for a short time these bacteria increase enormously, 

 until, when ready for churning, the average number is about 300 millions 

 per cubic centimetre. Now the sourness is caused by these bacteria, 

 and among them those producing lactic acid are the most prominent. 

 This must necessarily be the case, for some of the lactic-acid bacteria 

 are extremely common in nature, and thrive better in cream than 

 other bacteria do. There are over a hundred known species which can 

 produce lactic acid in milk, and of these the best known are Bacillus 

 acidi lactici, Streptococcus acidi lactici, Micrococcus acidi lactici, and 

 Micrococcus lactis. Recent work, however, tends to show that the 

 souring of milk is almost always accomplished by one or two species, 

 notably Bacillus acidi lactici, the reason being that this organism 

 thrives uncommonly well in cream, and being also so plentiful in 

 nature, very few creams escape infection .by it. This suits the purposes 



