2 A Handbook for Dairymen 



milk products furnish their food, but high tempera- 

 ture will kill them and low temperature will retard 

 their growth. 



Professor W. A. Stocking in an interesting ex- 

 periment shows the effect of temperature on the 

 development of bacteria in milk. A sample of milk 

 was thoroughly mixed and divided into six equal 

 parts. The six bottles were placed in water at dif- 

 ferent temperatures for twelve hours, at which time 

 the germ content of each lot was determined. The 

 bottles were then all placed together in a tempera- 

 ture of 70° F. and allowed to remain until they 

 curdled. As each sample curdled, the time was re- 

 corded. Results show what may happen easily in 

 milk which is allowed to stand overnight without 

 thorough cooling. 



Effect of Different Temperatures, Maintained for 



Twelve Hours, on the Growth of Bacteria and on the 



Keeping Quality of Milk 



I II 



Kept at 45 degrees Kept at SO degrees 



Number of bacteria, 9300 Number of bacteria, 18,000 



Curdled in 75 hours Curdled in 72 hours 



III IV 



Kept at 55 degrees Kept at 60 degrees 



Number of bacteria, 38,000 Number of bacteria, 453,000 



Curdled in +9 hours Curdled in 43 hours 



V VI 



Kept at 70 degrees Kept at 80 degrees 



Number of bacteria, 8,800,000 Number of bacteria, 55,300,000 



Curdled in 32 hours Curdled in 28 hours 



In cheese and butter making, the growth of cer- 

 tain types of organisms, Especially the lactic acid 

 type, is essential. In other dairy operations, such 

 as the handling of market or fluid milk, condensed 

 milk and evaporated milk, the growth of organisms 

 invariably causes the product to spoil. 



