PASTEURIZATION 187 



Principal Features of Diferent Types of Flash Pasteur- 

 izers. The flash, or continuous pasteurizers are principally of 

 three types. 1. Those consisting of a hollow drum, equipped 

 with a revolving agitator and surrounded by a heating jacket. 

 2. Those consisting of two hollow drums, the smaller rotating 

 inside the larger one and with the heating or cooling medium 

 circulating in the inner drum and in the jacket surrounding the 

 outer drum, while the cream passes in a thin film between the 

 heating surfaces of the two drums. The latter are frequently 

 of the regenerative type. 3. Those consisting of compartments 

 equipped with revolving discs which heat the cream while it 

 flows through the compartment. This type of pasteurizers 

 usually, though not always, contains also compartments for cool- 

 ing the heated cream. 



Some creameries use two flash pasteurizers, connected tan- 

 dem fashion, in the place of one. The machines are frequently 

 installed at different elevations. In the lower machine the cream 

 is heated to about 135 degrees F. and in the upper machine to 

 about 180 degrees F. The cream flows from the lower to the 

 upper machine and these pasteurizers may be so connected 

 that the first or lower machine is heated by the exhaust steam of 

 the upper or second machine, or each machine may be heated 

 with direct steam in which case they are generally installed side 

 by side on the same level. This double system of flash pasteur- 

 ization, when properly operated, helps to insure thoroughness 

 of heating. 



All of the flash pasteurizers with closed drums have the 

 power of elevating the cream, making unnecessary the use of 

 pumps to convey the pasteurized cream over the coolers or into 

 the vats. 



Some of the flash pasteurizers do part cooling of the heated 

 cream, while the remainder are heaters only and require sepa- 

 rate coolers. For this purpose surface coil coolers are most 

 generally installed. Frequently the surface cooler is done 

 away with and internal tube coolers or other coolers are used, 

 or the heated cream may flow direct from the flash pasteurizer 

 into the ripening vat where it is cooled by the revolving coil. 



