304 Tue Spray Process 
milk, without precondensing, was sprayed, and while this pro- 
cedure is entirely feasible, it was soon found that it was more 
economical to remove a considerable portion of the water of the 
fluid milk and to reduce the product to a concentration of about 
4:1 or 4.5:1 before spraying. This is accomplished by condens- 
ing the fluid milk by any of the methods for condensing as de- 
scribed under the ‘Manufacture of Condensed Milk” in this 
volume. In general practice the vacuum pan is used for this 
purpose in most of the milk powder plants. 
Effect of Pre-condensing on Economy of Manufacture.— 
The chief advantage and purpose of pre-condensing, instead 
of spraying the fluid, or uncondensed milk, lies in the greater 
economy of operation in the case of pre-condensing. 
The fluid milk contains more water than the condensed 
milk; more water must be removed during the spraying process, 
hence less milk can be desiccated in equipment of the same capa- 
city and in the same space of time than in the case of spraying 
pre-condensed milk. The pre-condensing therefore means greater 
capacity of the available equipment- shorter hours and greater 
economy of operation. 
Again, the fuel requirements are greater in the process of 
desiccating by the spray method than by evaporation in the 
vacuum pan or the film method. The comparative efficiency 
of evaporating water by means of air and in vacuum, is well 
understood. The heat-transmitting coefficient of air is much 
lower than that of steam and metal heating surfaces. The 
heat applied in the form of heated air is less completely utilized 
than the heat applied in the form of steam in copper jackets and 
coils, hence in evaporation by heated air there is greater waste 
of heat and fuel. The various factors which enter into the dry- 
ing by means of air and the resulting losses of heat transferred 
are discussed in detail by FE. Hausbrand' in his revised treatise 
entitled “ Drying by Means of Air and Steam.” 
Effect of Pre-condensing on Bulkiness of Spray Milk 
Powder.—Other conditions, such as orifice of spray nozzle, 
pressure of milk, and temperature to which the milk is preheated 
being the same, the milk powder made by spraying fluid or un- 
condensed milk, is somewhat more bulky than that made by 
1 Hausbrand. “Drying by Means of Air and Steam,” 1901. 
