ALCOHOLIC FERMENTATION 193 



The second group of bacteria that produce a ropy change 

 in milk are aerobic, and therefore only the upper layers 

 of the milk show an abnormal condition. It is most com- 

 monly noted in milk stored at rather low temperatures for 

 a period of from twenty-four to thirty-six hours. Out- 

 breaks of this trouble often cause extensive losses in the 

 milk-distributing business. It seems probable that uten- 

 sils, once infected, become a constant source of infection of 

 milk. Remedial measures should always include the thor- 

 ough scalding of the utensils. There is no reason to be- 

 lieve that the milk in which either of these groups of or- 

 ganisms has grown is in any way unhealthful. 



Various other abnormal fermentations are sometimes 

 noted in milk when the lactic bacteria are replaced by 

 other groups. Many bacteria produce colored by-products, 

 and when such organisms grow in milk to any extent a color 

 may be imparted to the same. The appearance of red and 

 blue milk is thus explained. Bitter milk may be due to the 

 iii-rest ion of feeds that contain a bitter principle, or to the 

 production of soluble decomposition products by the putre- 

 factive bacteria. Some acid-forming bacteria produce bit- 

 ter fla'vors. 



Alcoholic fermentation. When fruits such as the grape 

 and apple are pressed, and the juice allowed to undergo 

 spontaneous decomposition, the sugar will be fermented 

 with the production of alcohol and carbon-dioxide. This 

 fermentation is due to the yeasts that are present on the 

 fruit, having been carried there from the soil by dust and 

 insects. Any rupture of the skin allows the juice to exude, 

 and thus the growth of yeast on unpicked fruit is possible. 

 The juice is more heavily seeded with bacteria and molds 

 than it is with yeasts. The acidity of the juice is suffi- 

 ciently high to prevent the growth of most bacteria; the 

 molds do not find so* favorable an environment as do the 



