ALCOHOLIC FERMENTATION OF MILK. 95 



gated by adding to the fresh milk, after a brief boiling, a 

 little of an old sample of fermented milk which is kept on 

 hand in the same way as the liquid baker's yeast was pre- 

 served thirty years ago. The fermentation is a rapid one, 

 only about six hours being required. In general character it 

 resembles closely the other alcoholic fermentations. A study 

 of the product shows that here, too, is a growth of a variety of 

 microorganisms. There is a yeast present and at least three 

 species of bacteria producing lactic acid and rennet, and one 

 species of mold. These growing together produce the 

 alcoholic fermentation, but it is unknown exactly .what rela- 

 tion each species has to the peculiar fermentation that occurs. 

 A material of the same name, but prepared differently, is 

 made by the Algerians, and the Don Cossacks have a fer- 

 mented milk called aryan. 



It will be noticed that in all of these types of alcoholic 

 fermented milk a yeast is present and a number of other 

 organisms, among which there are, in all cases, lactic bac- 

 teria. Probably the lactic organisms in some way change 

 the character of the milk sugar by so altering the chemical 

 figuration of its molecule that it is easily capable of under- 

 going alcoholic fermentation, and that the yeast then pro- 

 duces such a fermentation. 



There are a number of commercial products resembling 

 those mentioned which, in recent years, have been placed 

 upon the market. The method by which they are prepared 

 is frequently a commercial secret, but they are always the 

 result of the growth of microorganisms, and prob- 

 ably in all cases the fermentation is produced by a combina- 

 tion of the action of microorganisms and yeasts; the latter 

 producing the alcoholic fermentation proper, after the 

 former have prepared the milk for such a change. They 

 are not as yet very important products and little is known to 

 science of their nature. 



