Preservation of Milk. 129 



Many devices have been proposed for the heating and 

 cooling of the milk. In many of the pasteurizers, the 

 milk flows in a thin stream over a metal surface, on the 

 opposite side of which is the heating agent, usually 

 steam; while in others, the milk is allowed to flow 

 through a vat in which revolve a series of discs into 

 which steam is passed. The discs are of considerable 

 size; thus, making a large heating surface; the milk is 

 thus heated quickly, and is constantly stirred by the ro- 

 tation of the heating discs. In other types the milk 

 passes into the bottom of a chamber in which a dasher 

 revolves at a rapid rate. This catches the milk, throwing 

 it in a thin film onto the wall of the chamber, which is 

 heated with steam on the opposite side. From such ma- 

 chines, of which the Fjord, the Jensen, and the Reid ma- 

 chines are types, the milk may be forced to a considera- 

 ble height. These are widely used in this country for 

 the pasteurization of milk and cream for butter making. 



Milk that has been heated must be cooled at once by 

 the use of cold water and ice. In order to economize in 

 the use of both steam and cooling agents, the so-called 

 regenerative machines were devised. The essential feat- 

 ure of these machines lies in the fact that the cold milk 

 inlet and the hot milk outlet are on opposite sides of a 

 single partition ; thus the inflowing cold milk is partially 

 heated by means of the already treated hot milk which 

 it is desired to cool. 



In order to avoid the disadvantages of the continuous 

 machines, viz., lack of control, an apparatus has recently 

 been devised which can handle large quantities of milk, 

 heating the same to any temperature for any desired 

 time. In such a machine the milk is first heated in a 

 continuous heater, and is then passed into large tanks in 

 which it is allowed to remain for the desired time, and 

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