284 FERMENTATIONS IN MILK 



weeds, such as chicory, tansy, and wild chamomile. Cows 

 with udder disease also yield bitter milk occasionally. 



In all these instances the bitterness is recognisable in 

 the milk as it is drawn from the animal, and it does not 

 increase with age of the milk. 



There are, however, many cases recorded of serious 

 bitterness of milk which have originated through the 

 activity of bacteria. 



In boiled milk the bitter flavour not infrequently 

 arises from the spore-bearing organisms, such as Bs. 

 subtilis and its allies, as well as some of the butyric acid 

 organisms : in unboiled samples these bacteria are 

 generally kept in check by the lactic acid organisms. 



In fresh milk bitterness may arise ; the trouble in 

 many cases has been traced to the contamination with 

 various kinds of bacteria. Varieties of Bact. coli and 

 Bact. lactis aerogenes have been found capable of inducing 

 the objectionable change in milk, the peculiar taste being 

 brought about in most cases by decomposition of the 

 protein of the milk. Freudenreich isolated from bitter 

 cheese a small coccus, which he named Micrococcus casei 

 ainari. It liquefies gelatine, renders milk acid, and coagu- 

 lates the casein, producing at the same time a bitter taste. 



The same writer described a motile bacillus obtained 

 from bitter cream which liquefies gelatine and gives rise 

 to an intensely bitter flavour in milk, and coagulates it 

 without rendering it acid. 



Eckles has also described a small oval coccus capable 

 of giving rise to bitterness in milk, and rendering cheese 

 made from it very bitter (see p. 377). 



Harrison traced the bitterness of milk in a cheese 

 factory to contamination with a species of Torula or 

 non-sporing yeast (see p. 377). 



