CREAMLIRY BUTTUR MAKING 



65 



JIILK HEATERS. 



There are to be found upon the market two general 

 classes of milk heaters : Those which admit the steam 

 directly to the milk called direct heaters, and those in 

 which the steam enters a jacket surrounding the milk 

 known as indirect heaters. 



Direct Heaters. These are practically nothing more 

 than an expansion in the feed pipe in which the steam 



Fig- 21.— Twentietli Centur.v milk heater. 



enters the milk. They are permissible only when first 

 class steam is available and when milk is to be heated 

 through a short range of temperature. But even under 

 these conditions indirect heaters are always preferred. 



The two main objections to the direct heaters are: (i ) 

 the liability of contaminating the milk with impure steam, 

 and ( 2 ) the effect of the sudden heating upon the loss 

 of fat in the skim-milk which may be quite considerable 

 when the milk is heated through a long range of 

 temperature. 



Indirect Heaters. Figs. 20 and 21 illustrate this t\pe 

 of heaters. In the Curtis heater the milk circulates in a 



