98 DAIRY TECHNOLOGY 



For this reason, some filter and clarify the milk. Milk 

 filters have not given much satisfaction and are not used 

 to any considerable extent. But the clarifying of milk 

 by centrifugal force is being adopted to a large extent by 

 city milk plants. Some of them use an ordinary cream 

 separator and run the cream and skim milk together. At 

 times the milk is standardized to the desired percentage of 

 fat. 



The milk clarifier is a modification of the cream separa- 

 tor, providing a greater capacity for the deposit of sedi- 

 ment and delivering the whole milk from the machine 

 instead of separating it. Removing dirt from milk re- 

 moves some bacteria, leucocytes, etc., so that the clarified 

 milk is a purer and cleaner food. 



Pasteurization and Cooling. — The large city milk plant 

 commonly pasteurizes the milk, and for this purpose an 

 intermittent pasteurizer or a continuous machine with a 

 retarder is used, usually the latter. The milk is heated to 

 from 140° to 160° F. and held at that temperature for from 

 15 to 30 minutes, when it is discharged and conducted to 

 the cooler. This latter is very commonly a vertical coil 

 of pipes over which the milk flows in very thin sheets, 

 while at the same time cold water or brine is flowing through 

 the interior of the pipes, entering at the bottom and flow- 

 ing out at the top. 



The pasteurization of milk, to be successful from a 

 commercial standpoint, must be so carried on that the 

 keeping qualities of the milk will be improved without 

 heating to such an extent as to impart a cooked flavor or 

 materiafly to injure the creaming qualities of the milk. 

 It is a well-known fact among dairymen, that excessive 

 heating and stirring of milk breaks the clusters of fat 

 globules and scatters them throughout the serum. This 



