1 62 FERMENTATION IN MILK 



by itself. The organisms discovered by Prazmowski and Pasteur 

 were anaerobic. But Fitz and Hueppe isolated an aerobic butyric 

 bacillus. 



This fact was confirmed by Gruber, working with a pure 

 culture in 1887, and it was at the same time demonstrated that the 

 Clostridium butyricum of Prazmowski consists of a number of 

 closely allied, but distinct, species. Lafar states that nearly related 

 to this is a ferment isolated by Liborius from old cheese, and 

 introduced into literature under the name of Clostridium foetidum. 

 This organism liberates foul-smelling gases, in addition to pro- 

 ducing butyric acid, and forms one of the many connecting links 

 between the butyric acid bacteria and the so-called " potato " 

 bacilli. No sharply defined limit can be drawn between these two 

 groups. 



The butyric acid bacteria which produce aromatic substances 

 are important for the ripening of cheese, and to this subject we 

 shall refer again subsequently. Freudenreich separated from milk 

 a Clostridium foetidum lactis, which develops, in this medium, an 

 odour resembling that of Limburger cheese, and the same observa- 

 tion was made by H. Weigmann. Winogradsky isolated the 

 butyric Clostridium Pasteurianuni ; and Baier, Weigmann, Behrens, 

 and others described other butyric-producing bacteria. Butyric 

 acid is to be regarded in some ways as an end product of a long 

 series of fermentative changes. It is accompanied by many by- 

 products, and is a complex process. There are therefore many 

 organisms which, although not designated butyric acid bacilli, have, 

 in fact, the capacity of producing butyric acid amongst other 

 substances. In ordinary cream ripening it is absent, and therefore 

 not of much utility in the dairy industry. In the ripening of cheese 

 it may play some part, and certainly does so in the rancidity of 

 butter. 



3. Alcoholic Fermentation in Milk 



Solutions containing sugar, if exposed to the air, are apt to 

 undergo alcoholic fermentation, and milk is no exception to the 

 rule. The change is, of course, due to saccharomyces of different 

 kinds, which have the power of breaking up the lactose and pro- 

 ducing alcohol and carbonic acid gas. At the same time, it must 

 be said that lactose is not readily acted upon in this way, and 

 the percentages of alcohol produced in milk are very small in 

 comparison with those occurring after vinous fermentation. It 

 generally occurs in two stages. The lactose is first inverted, 



