92 SWEETENED CONDENSED M1iL«K—CoNDENSING 
With a low capacity vacuum pump, or a pump running 
irregularly, or too slow, or too fast, and with leaky joints, the 
vacuum will always be low, and the pressure and temperature 
relatively high. Under these conditions the pan is difficult to 
operate and evaporation is slow. 
With the above conditions under control and properly adjus- 
ted and with a given area of heating surface and arrangements of 
it for preper circulation of the milk, the temperature and the 
rapidity of evaporation depend on the steam pressure in the 
jacket and coils and on the amount and temperature of the water 
used in the condenser. 
Twenty-five pounds of steam pressure in the jacket and coils 
has been found to be about the maximum that can safely be used. 
\WWith this steam pressure the milk coming in direct contact with 
the heating surface is exposed to about 267 degrees F. and there 
is a tendency for some of it to bake or burn on, which is unde- 
sirable. The walls of the jacket and coils are also subjected to 
considerable strain, since they are surrounded by an almost com- 
plete vacuum. Then again, if the pan has the proper amount 
of heating surface the capacity of the condenser and the water 
supply are in most cases insufficient to take care of and condense 
the vapors arising from the boiling milk in the pan, when the 
steam pressure in jacket and coils approaches or exceeds twenty- 
five pounds. Most condenseries operate their pans with five to 
hfteen pounds of steam pressure in jacket and coils. In the oper- 
ation of some pans not more than about five pounds steam pres- 
sure can be used economically in jacket and coils, because the use 
of more steam causes the steam to blow through and out of the 
coils. 
Aside from the principle of construction the capacity of the 
condenser used in milk condenseries is very largely dependent on 
the water supply. \Whenever the condenser is forced beyond its 
capacity, by using excessive steam in jacket and coils, the vacuum 
drops, the temperature rises and the process of evaporation is 
retarded. 
The higher the vacuum the more rapid the evaporation, A 
rise in the steam pressure in the jacket and coils increases the 
