92 SWEETENED CONDENSED MILK 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 proper 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. 

 With 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 ag~ain, 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 

 fifteen 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. W 7 he'never 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 



