THE PASTEURIZATION OF MILK 



tain minimum amount. One of the simplest meth- 

 ods of steam pressure control is by an instrument 

 constructed like the safety valve of a boiler. A 

 movable weight upon an arm regulates the pressure 

 which is desired. When properly set any increase 

 of pressure above the desired amount lifts the arm 

 and shuts the steam valve connecting with the pipe 

 leading to the heater. Other more complicated 

 forms of apparatus are on the market, the details 

 of which it is not necessary to describe. 



In the matter of the control of the temperature 

 at which the milk leaves the heater, it is, of course, 

 possible to do this by hand. This method makes it 

 necessary that a man constantly watch the ther- 

 mometer attached to the outlet milk pipe, and at 

 the same time open or close the steam valve to ad- 

 just the steam flow to the varying temperature of 

 the milk. 



If the speed of milk flow, and also the steam 

 pressure is well controlled, it is possible for a care- 

 ful workman to regulate the milk temperature with 

 good success. If, however, these factors are con- 

 stantly varying, it is nearly impossible for even a 

 careful man to obtain good results. It is, of course, 

 more economically efficient to arrange for auto- 

 134 



