DAIRYING 



75 



Plate 29. Arrangement of equipment for a pasteurizing plant. 



bacteria spores which were not destroyed have changed the nitro- 

 genous constituents of the milk into products that are quite dif- 

 ferent from those noticed in ordinary sour milk. These same 

 putrefactive changes take place to a certain extent in the normal 

 souring of milk which has not been pasteurized, but the predom- 

 inating odor and taste of such sour milk come from the products 

 of the lactic acid fermentations and they are sufficiently pro- 

 lounced to make the putrefactive odors less noticeable. 



Various names have been given to the process of milk pas- 

 teurization depending on the method used for heating the milk. 



801. Home Pasteurization is done by using the "double 

 toiler." As soon as the water boils in this boiler it is taken off 

 the stove, the milk added and after covering the boiler is al- 

 lowed to stand at least 20 minutes. Milk treated in this way is 

 usually heated to 165 F. It should then be cooled to near 40 F. 

 and kept cold until needed. 



INTERMITTENT OR "HELD" PASTEURIZATION. 



802. When the application of pasteurization was first pro- 

 posed for preserving milk and cream it was deemed necessary to 

 heat these to about 155 F. and hold them at this temperature for 

 15 to 30 minutes. This continued heating was supposed to be 

 needed to destroy all disease germs that might be present and it 



