252 THE FERMENTATION OF CHEESE 



the subject falls within the present section, which deals with the decomposition 

 of albumin. 



Niigeli was the first to attribute the development of bitter flavour in milk to 

 bacterial activity, and since then many attempts have been made to find and 

 prepare pure cultures of bacteria possessing such properties. Some of these are 

 capable of producing bitter principles both in milk and cheese, whilst others are 

 injurious solely to the former; but all liquefy gelatin, and consequently produce 

 a peptic ferment. 



Of the first group two species are known up to the present, viz., (i) Tyrot/<ri.i- 

 geniculatus obtained as a pure culture by DUCLAUX (XIII.) from Cantal cheese, 

 and already noticed in 176 produces a bitter substance in both milk and soft 

 cheese. (2) MierocoeouB casei amari was isolated to a pure culture by FREUDEN- 

 REICH (X.) in 1894 from bitter, hard, Swiss cheese. This organism, which 

 measures about i p. in diameter, is endowed with the somewhat rare dual property 

 of forming lactic acid and liquefying gelatin. In milk and cheese but not in 

 bouillon it gives rise to a strongly bitter flavour, which Freudenreich only 

 partly ascribes to the peptone produced, since after the latter has been thrown 

 down by alcohol from milk cultures of the coccus, the filtered liquid leaves, on 

 evaporation, a bitter residue. Here the widespread experience of practical 

 cheese-makers, viz., that the bitter taste generally makes its appearance at the 

 stage of semi-ripeness, vanishing again as the cheese increases in age, may be 

 mentioned. 



The capacity of developing a bitter flavour in milk alone is possessed by the 

 following organisms: i. Weigmann described in his above-named treatise a 

 sporogenic bacillus, 1.5-1.8 p. long and 0.9-1.1 p. broad, which does not produce 

 gas, bub gives rise to a casein- dissolving enzyme and a volatile acid (differing 

 from butyric acid). 2. The micrococcus of bitter milk, of CONN (IV.), is aerobic 

 and non-motile, forms butyric acid, and develops a repulsive bitter flavour in 

 milk, cream, and butter. 3. M. BLEISCU (I.) obtained from milk, which had 

 become decomposed after sterilisation by the Neuhauss process, a pure culture 

 of a facultatively anaerobic motile bacillus, whose endogenous spores were 

 able to stand exposure^ for six hours at a temperature of 100 C. in milk. 

 When inoculated into sterilised milk it produces a strongly bitter flavour, and 

 must, from its behavour towards casein, be grouped with Duclaux' Tyrothrix 

 species. 4. Bacillus liquefaciens lactis amari was found by FREUDENREICH (X.) 

 in cream which had turned bitter spontaneously. The relative dimensions of 

 this motile bacillus vary considerably : the most usual measurements are 0.5 jj. 

 for the breadth and 1.5 /* for the length, but the latter may extend to 6 /^. It 

 induces coagulation in milk which it also makes very bitter but no formation 

 of acid takes place ; and it liquefies gelatin. 



