CONTINUOUS PROCESS EVAPORATORS 167 



on the start, and to finish the evaporation between 90 and 100 

 degrees F. The air blast is so introduced as to keep the milk 

 along the heating surface of the jacket and coils in circulation 

 and. therefore, prevent largely the baking of the milk on the 

 heating surface. After the milk has been evaporated to a certain 

 degree of concentration, say 2:1. it is transferred to the auxiliary 

 evaporating tank where the condensation is completed. This 

 transfer is not necessary, but is resorted to solely as a conve- 

 nience, in order to continue treatment of the reduced bulk of 

 material in a smaller tank and leave the larger tank free for 

 treating a fresh batch of milk, and further, because there are 

 no obstructing coils in the auxiliary tank, interfering with the 

 drawing off of the finished and thick condensed milk. In this proc- 

 ess, as now used, the milk is usually first separated and the 

 skim milk only is condensed. The cream is subsequently added 

 to the condensed skim milk. 



Advantages and Disadvantages of Campbell Process. The 

 initial cost of installing the necessary machinery is much less 

 than where vacuum evaporation is practiced. The low heat 

 applied makes it possible for the finished product to retain the 

 properties of raw milk, leaving the albumenoids and lime salts 

 in their original and easily digestible form and preserving the 

 antiscorbutic vitamines in active form. 



This process is applicable only in the manufacture of. un- 

 sweetened condensed milk. Unless subsequently sterilized, the 

 product will keep for a short time only. This process has at the 

 present time only very limited use. It can hardly be considered 

 as an important branch of the condensed milk industry. 



ClIAI'TKR XIV. 



CONDENSING MILK BY CONTINUOUS PROCESS. 



The processes of condensing milk described in preceding 

 chapters, are exclusively confined to the intermittent or batch- 

 principle of evaporation. That is in the case of the vacuum pan, 

 the fresh milk runs into the pan until the capacity of the pan is 

 reached and no condensed milk leaves the pan until the con- 

 densation of the entire batch is completed. Then the pan must 

 be emptied before more milk can be drawn in. In a similar man- 

 ner, in the Campbell process, evaporation of the entire batch 



