THE COST OF PASTEURIZING MILK AND CREAM. 
9 
however, is practically doubled when steam is taken direct from the 
boiler for pasteurizing instead of utilizing the exhaust steam. The 
steam pressure is reduced from boiler pressure to about 3 pounds by 
some form of reducing valve, consequently there is approximately as 
much heat in the exhaust steam from the engine, or steam-driven 
auxiliaries, as there is in steam taken from the boiler. The amount 
of fuel mentioned above is for pasteurizing, and is not to be confused 
with the total amount used in firing the boilers. In other words, 
it is the fuel required to evaporate in the boiler a certain amount 
of water which is used for the purpose of pasteurizing the cream. 
With this arrangement the pasteurizing was done with heat that 
would otherwise have been wasted, and furthermore it took a load of 
67.1 horsepower off the boiler plant. 1 
TESTS NOS. 2, 3, AND 4. 
Tests Nos. 2 and 3 were also made with exhaust steam, but the 
arrangements were different from the foregoing, as the exhaust 
from the engines was piped directly into the heater. The only 
load on the engines at the time was the pasteurizers and the centrif- 
ugal cream separators, which amounted to very little. The exhaust 
steam available, however, was sufficient to operate the pasteurizers 
up to their full capacity. 
Referring to the summary of the tests in Table 2 it will be noted 
that the fifth item, "Heat in steam required to drive pasteurizing 
equipment," is blank except for test No. 4. The reason for this 
is that the engine or steam-driven auxiliaries from which exhaust 
steam was used for pasteurizing are considered in the light of pressure- 
reducing valves, the mechanical power being, so to speak, a by- 
product. That is to say, there is a loss of heat in steam due to drop in 
pressure, and while the wire drawing of the steam through the valve 
will superheat the steam to a certain extent, the loss may be con- 
sidered the same for the purpose of this paper, regardless of whether 
this drop is caused by passing through a pressure-reducing valve or 
through a steam engine. In test No. 4 the steam used for pasteuriz- 
ing was reduced in pressure by a valve, consequently the energy 
represented by the difference in pressure and temperature of the 
steam before and after passing through the reducing valve is a 
clear loss. In neither case, however, was the heat lost due to drop 
in pressure of the steam available for heating the cream. The 
380,800 B. t. u. in column 4 represents the heat in the steam at 
boiler pressure which was used in the engine for driving the pasteur- 
izer, separator, shafting, etc., required in the process of pasteurizing, 
and as the exhaust from the engine was allowed to go to waste it is 
1 The use of exhaust steam for other purposes in milk plants is treated in Bureau of Animal Industry- 
Circular 209. 
