82 THE MARKETING OF WHOLE MILK: 



for delivery, or, if delivery is made the following morning, 

 transferring to a refrigerator; and (6) delivery; or the 

 milk may pass from the weigh can to a pasteurizer supply 

 can, thence to a pasteurizer and to a cooler before being 

 bottled. 



In big city plants the whole process is more complex 

 and is usually accomplished by larger and more efficient 

 machinery. Here the milk is received in a special receiv- 

 ing room, where it is inspected. It is then strained into a 

 weigh can, weighed, and, when purchased by test, sampled 

 for further testing. From the weigh can it is often pumped 

 to the upper floor of the plant into a supply tank, in order 

 that gravity may be used in all further transfers. From 

 the supply tank it passes to the pasteurizer. Three sys- 

 tems of pasteurization are in common use. (i) The flash 

 system is perhaps the most frequently used. Under this 

 system the milk is heated from 145 to 160 degrees Fahren- 

 heit for an instant and then passed over cooling pipes. 

 (2) The holding system requires that the milk be heated 

 to about 145 degrees, usually by means of the pasteurizer 

 employed in the flash system. In contrast to the flash 

 system, the milk, instead of being cooled at once, is held 

 at 145 degrees for thirty minutes. This system is perhaps 

 the best in common use. Apparatus has been devised 

 which automatically holds milk for the required time in 

 such a way that although it enters and leaves the pasteu- 

 rizer in a steady stream, successive compartments are 

 filled and then emptied after their contents have been 

 heated and held the required time. Pasteurizing at 145 

 degrees and holding for thirty minutes does not appreci- 

 ably change the chemical composition of the milk, nor 

 does it injure the cream line. The Chicago Board of 

 Health, as well as the boards of health in many other 



