96 MARKET DAIRYING 
which permit the steam to enter a jacket surrounding 
the milk, known as indirect heaters. Only idirect 
heaters should be used in heating milk to the separating 
temperature. 
The two main objections to the direct heaters are: (1) 
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 tem- 
perature. 
It is well known that the exhaustiveness of skimming 
with any separator is greatly influenced by the manner 
in which the milk is heated. In general very sudden 
heating has the effect of diminishing the difference in 
the specific gravity between the fat and milk serum, con- 
sequently rendering the separation of the fat from the 
milk more difficult. 
In experiments conducted by the author it was found 
that in many instances where the milk was received in 
a partly frozen condition and suddenly heated to a sepa- 
rating temperature of 80° to 85° F., the loss of fat in the 
skim-milk was from .08% to .12%. 
The addition of water to the milk through the con- 
densation of the steam is also objectionable in heating 
milk with steam direct. The practice of turning steam 
into milk should therefore be abandoned. 
