THE PASTEURIZATION OF MILK 



the method of construction, the percentage of hold- 

 ing time to filling time is from 25 per cent, to 70 

 per cent. It is usual to estimate the time as 60 per 

 cent, of the filling time. It is true that tanks which 

 are tall and of comparatively narrow diameter are 

 more efficient than are short and wide tanks, the 

 reason probably being that with long, narrow tanks 

 the movement of milk is comparatively rapid, and 

 there is less diffusion of the milk than when the 

 movement is slow, as in the wide, short tank. Tests 

 have been made which indicate that when the rate 

 of flow is twelve feet or over a minute, there is 

 very little diffusion of the liquid. 



In all tanks of this character it is desirable, and 

 indeed almost a necessity, that some sort of an 

 insulating jacket be provided in order that there 

 be as little loss of temperature as possible during 

 the holding process. The reason for this, as be- 

 fore stated, is that the cooling of the milk which 

 is near the outer circumference of the tank causes 

 downward currents. Thus the milk which falls 

 to the bottom on account of these currents is car- 

 ried out of the tank before it has been held for the 

 proper length of time. 



The insulation may be provided by means of 

 120 



