Sweetened Condensed Milk — Condensing 83 



With a low capacity vacuum pump, or a pump running irreg- 

 ularly, 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 evapora- 

 tion is slow. 



With the above conditions under control and properly adjusted, 

 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 undesirable. 

 The walls of the jacket and coils are also subjected to considerable 

 strain, since they are surrounded by an almost complete 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 con- 

 denseries operate their pans with twelve to twenty pounds of steam 

 pressure in jacket and coils. In the operation of some 'pans not 

 more than about five pounds steam pressure 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. This may be due to relatively 

 large heating surface, or small evclporating capacity due to a small 

 capacity pump or limited water supply to condenser. 



The capacity of the condenser used in milk condenseries is 

 very, largely dependent on the water supply. Whenever the con- 

 denser 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 rapidity 



