1934 The Cornell Reading-Courses 



the large concrete or tile sterilizers, it may require from twenty to thirty 

 minutes. 



COOLING 



If the bacteria count of milk is to be kept low, it is absolutely necessary 

 to keep milk cool. Not all bacteria multiply at the same rate, but some 

 of them multiply as often as every twenty minutes under favorable con- 

 ditions. It is easily seen that even with a small initial contamination, 

 the bacteria count of a sample of milk would, under favorable conditions, 

 soon amount to hundreds of thousands of germs per cubic centimeter. 

 The manner of cooling milk on farms varies, but the method used does 

 not matter provided a few precautions are observed. The milk should 

 be cooled quickly in order to prevent bacterial growth, as shown by the 

 following table : 



Effect of Different Temperatures for Twelve Hours on the Growth of 

 Bacteria and on the Keeping Quality of Milk 



I II 



Kept at 45° F. * Kept at 50° F. 



Number of bacteria, 9,300 Number of bacteria, 18,000 



Curdled in 75 hours Curdled in 72 hours 



III IV 



Kept at 55° F. Kept at 60° F. 



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



Curdled in 49 hours Curdled in 43 hours 



V VI 



Kept at 70° F. Kept at 80° F. 



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



Curdled in 32 hours Curdled in 28 hours 



The cooling should be done in a place free from dust, odors, flies, and 

 contamination from cats and dogs. The cooler, or the utensil in which the 

 milk is cooled, must be clean and, as far as possible, sterile. Care must 

 be taken to prevent the refrigerating substances from spattering into 

 the milk. Probably one of the most satisfactory methods of cooling 

 milk on farms is to set the cans of milk in a tank of ice water. Any tank 

 may be used for the purpose, but one made of cement is best because it 

 is durable and easy to clean. One thing must be emphasized, that is, the 

 necessity of stirring the milk at least every ten minutes during the process 

 of cooling. If the milk is not stirred, that around the inside of the can 

 will cool rapidly, while that in the center of the can will remain com- 

 paratively warm. 



THE CARE OF MILK IN THE HOME 



If the producer and the dealer follow out the suggestions given in this 

 lesson, the consurner will receive clean, cold milk, After the milkman 



