OF PASTEURIZATION 213 



vat with revolving coil. In the case of the flash process the 

 same type of vat is needed to hold, ripen and cool the cream, 

 but in addition to this there must be installed the flash 

 pasteurizer and the cooler (unless all the cooling is done in the 

 vat) and there is further need of at least two forewarmers. 

 This extra equipment is partly offset by the fact that the flash 

 pasteurizer increases the vat capacity, hence fewer vats are 

 needed by this system of pasteurization. The upkeep of the 

 vats used for pasteurizing is much greater than the upkeep of 

 the flash machine as already explained under "Durability." The 

 labor needed for operation is very similar with both systems 

 except that of cleaning which is greater in the case of vat 

 pasteurizers. 



The cost of fuel for heating and cooling is somewhat higher 

 in the case of flash pasteurization than in the case of vat pasteuri- 

 zation. More heat is required to raise the temperature of the 

 cream to 180 degrees F. of flash pasteurization than to 145 de- 

 grees F. of vat pasteurization, and the cooling of the hotter, 

 flash-heated cream involves the use of correspondingly more 

 cooling medium than the cooling of the less hot cream of the 

 holding process. 



EFFECT OF PASTEURIZATION ON QUALITY OF 



BUTTER 



Germ-Killing Efficiency. The germ-killing efficiency of vat 

 pasteurization at 145 degrees F. and holding for thirty minutes, 

 and flash pasteurization at 180 degrees F. is practically the same. 

 When properly operated the two processes destroy over 99 per 

 cent of the bacteria, yeast and molds, present in the cream. From 

 the standpoint of prevention of bacterial action in butter it 

 would seem, therefore, that both processes are equally efficient. 



Effect on Enzymes. The effect of the two processes of 

 pasteurization on enzymes present in the cream, both, those 

 which are inherent in milk and those which may have developed 

 as the result of bacterial action before pasteurization, must of 

 necessity be quite dissimilar. Exposure to a temperature of 176 

 degrees F. or over is destructive to the activity of most of the 

 enzymes naturally present, while at 145 degrees F. enzyme ac- 

 tion is not destroyed. 



