204 PASTEURIZATION 



the air is more apt to become coated with cooked cream than 

 the submerged coil. A submerged coil precludes all danger of 

 excessive foaming and of whipping air into the cream, while 

 an exposed coil is bound to incorporate air in the cream and 

 the more the coil projects above the cream the more pronounced 

 is this objection. An exposed coil also invariably causes much 

 splashing of the cream, which is objectionable. 



Because of the objection of operating the vat with the coil 

 projecting above the cream, vat pasteurizers in which the coils 

 are set low are preferable to those in which the coils extend to 

 the top of the vat. 



For this same reason vat pasteurizers of cylindrical shape 

 and with a vertical, suspended coil are superior to vats with 

 horizontal coils. In the cylindrical vat the motion of the coil 

 spiral is upward, and out of the cream, making impossible the 

 mixing of air with the cream, while in the vat with the horizontal 

 coil the spiral of the coil moves downward into the cream. 



Temperature and Time of Exposure. The heating should 

 be done as rapidly as the supply of steam, the available heating 

 surface and the circulating system permit. The cream should 

 be heated to 145 degrees F., and held at that temperature at 

 least twenty and preferably thirty minutes. 



Slow heating and prolonged holding at 145 degrees F. are 

 prone to produce cream and butter with a mealy body. Under 

 proper conditions the heating of the cream to 145 degrees F. 

 should not occupy more than about fifteen to twenty minutes. 



Experimental 1 results have shown that when holding the 

 cream at 145 degrees F. for a shorter time than twenty minutes, 

 the germ-killing efficiency suffers. This is clearly demonstrated 

 in Table 36. 



As soon as the temperature has reached 145 degrees F. a 

 pail full of the hot cream should be drawn from the gate of the 

 vat and poured back into the vat. The nipple at the gate con- 



1 Hunziker, Mills and Spltzer, Pasteurization of Cream for Butter-making, 

 Purdue Bulletin, No. 203, 1917. 



