RELATION OF BACTERIA TO DAIRY PRODUCTS 551 



constant temperatures of 70° F. and 50° F. until they curdled. 

 The germ-content of each sample was obtained at each twelve- 

 hour period. 



Influence of Temperature on Growth of Bacteria and Keep- 

 ing Quality of Milk 



Held at 70° F. 



Held at 50° F. 



Age in 

 Hrs. 



Total Number 

 Bacteria 



Acid Bacteria 



Per Cent 

 of Acid 



Total Num- 

 ber Bacteria 



Acid Bac- 

 teria 



Per Cent 

 of Acid 





 12 



24 

 36 



3,000 



14,000 



4,477,000 



149,650,000 



Curdled i 



800 



9,400 



4,472,000 



149,600,000 



n 99 hours. 



.19 

 .20 

 .21 

 .26 



3,000 800 .19 



1,600 800 .19 



13,500 12,800 .20 



140,800 139,400 .20 



Curdled in 315 hours. 



Changes in milk due to bacteria (see Figs. 89, 90) 



In the handling of market milk, the object to be attained is 

 the delivery of the product to the consumer in as nearly as 

 possible the condition in which it left the udder of the healthy 

 cow, and the problem of the producer and dealer is to prevent 

 bacterial contamination and development. While these two 

 factors cannot be entirely eliminated, they can be very largely 

 controlled by methods of production and handling. Negli- 

 gence at any point in the life of the milk may seriously affect 

 the quality of the product. 



The most common change in milk is its souring. This 

 change is the result of the breaking down of the milk-sugar by 

 the bacteria and the production of lactic acid. It can be pre- 

 vented by holding the milk at low temperatures. 



Occasionally the milk dealer may be annoyed by such ab- 

 normal conditions as "sweet curdling 5 ' milk, "bitter" milk, 



