SWEETENED CONDENSED MILK CONDENSING 63 



It is probable that the name of this primitive apparatus was passed 

 on to the more perfected machinery now in use. 



The vacuum pans are constructed of copper, iron, steel or 

 bronze. Practically all of the vacuum pans used for condensing 

 milk are made of copper throughout ; they are of various styles 

 and sizes. The predominating size used in milk condenseries is 

 the "six-foot pan." By the term six-foot is meant a retort meas- 

 uring six feet in diameter. 



There are two general types of vacuum pans on the market ; 

 pans that are relatively wide in diameter and shallow in depth, and 

 pans of relatively narrow diameter and which have a deep body. 

 Both types are claimed, by their respective manufacturers, to have 

 special advantages, such as ease of operation, uniformity of action, 

 economy of fuel and of water, and rapidity of evaporation ; the 

 opinions of the users of these pans are also at variance concerning 

 their relative merits. 



The advocates of the wide, shallow pan claim that this type 

 of pan makes possible such an arrangement of the heating surface 

 as to take care of the maximum amount of milk with the minimum 

 depth of milk over the heating surface and that this arrangement 

 is most desirable. They hold that because the wide and shallow 

 pan offers a larger area of evaporating surface, it therefore makes 

 possible more rapid evaporation than the narrow, deep pan. They 

 further emphasize that in the wide, shallow pan, the milk boils 

 more quietly, is under better control and is less apt to be carried 

 over into the condenser and lost, than in the narrow, deep pan. 



The advocates of the narrow, deep pan claim that their type 

 of pan increases the rapidity of evaporation because it causes the 

 milk to pass over the heating surface more rapidly. When the 

 pan is in operation, the boiling milk travels from the center of the 

 bottom toward the periphery where it rises, rolls over the coils, 

 and returns to the center. It is claimed that a pan with a shallow 

 jacket, such as the narrow, deep pans have, causes the milk to roll 

 over higher, especially if the coils are close to the periphery and 

 leave plenty of vacant space in the center of the pan. This, in turn, 

 means more rapid circulation of the milk, causing it to pass over 

 the heating surface at greater speed, and oftener, which naturally 

 enables the milk to utilize more heat and, therefore, to evaporate 



