264 



Nature- Study Agriculture 



Cooling 

 the milk 



then be washed in very hot water containing sal soda. 

 A brush with a handle is much better than a cloth to rub 

 them with, for washing with a cloth held in the hand 

 does not permit the use of very hot water. Rinsing 

 should be done in clean, hot water, and then the vessels 

 should be left upside down to drain and dry without 

 being wiped (Fig. 209), for it is difficult to keep a drying 

 cloth sufficiently clean. 



One of the most important operations to prevent the 

 bacteria in milk from rapidly multiplying (Fig. 210) and 

 souring the milk is to cool it promptly after it is drawn 

 from the cow. In large dairies this is done by allowing 

 the milk to run over a framework of iron pipes within 

 which cold water or another cooling fluid circulates 

 (Fig. 211). Such a cooler should be used only in a 

 clean milk house where the air is free from dust. The 

 most convenient and sanitary way to cool milk in a 

 small dairy is to set the cans in cold water, stirring the 

 milk occasionally. 



75 O Bacteria 



5 Bacteria 



FIG. 210. The rates of increase of bacteria in milk at different temperatures. 



