SANITARY MILK PRODUCTION 



155 



more in the skim-milk than in the unskimmed milk. Heinemann and 

 Class continuing the experiment found that separated cream contains 

 fewer bacteria than the milk from which it is obtained, that the number 

 of bacteria in separated cream decreases proportionately as the fat con- 

 tent increases and that the number of bacteria in separated milk is larger 

 than the number in the milk from which it is obtained, if the cream con- 

 tains up to about 35 per cent, fat; above this percentage the number is 

 smaller. They found, too, that the number of bacteria in separated 

 milk decreases proportionately with increase of fat in separated 

 cream. 



Cooling of Milk. It is absolutely essential in order to prevent rapid 

 bacterial development in milk, with consequent deterioration thereof, 

 that it be cooled promptly after milking. On most farms the cooling 

 is done by setting the milk in a tub of well or ice water. The effective- 

 ness of this method is shown by the figures in Table 43. 



TABLE 43. THE COOLING OF CREAM IN CANS (U. S DEPT. OF AGRICULTURE) 



Many farmers instead of cooling milk in cans bring it to low tempera- 

 ture by running it over coolers. They are of various sorts but in all of 

 them the milk is cooled by flowing in a film over an extensive surface of 

 thin metal which is chilled by cold water or by brine. Coolers work 

 well when properly cared for but they cannot be neglected without 

 injury resulting to the milk for it flows over the entire surface of the 

 cooler and consequently picks up all the dirt there is on it. Whenever 

 steam is available coolers should be sterilized immediately before use. 

 In watching the cooling of milk one sometimes sees it refuse to flow over 

 a part of the cooler, which generally indicates that the spot is unclean. 

 Milk may be both contaminated and adulterated by the escape of water 

 or brine from a leaky cooler. Besides being contaminated by the cooler 

 the milk may be also, by the air, if the cooler is an open one and the 

 cooling is done in a dusty place. If the room is malodorous the milk may 



