Peoceedings of Seventeenth Xormal Institute 287 



render tubercle bacilli unable to produce tuberculosis, but this 

 margin of safety is narrow. A temperature of 178° F. will kill 

 disease-producing bacteria almost instantly, and when wbey is 

 held at that temperature for some time there is a wide margin of 

 safety. This temperature also produces chemical changes in the 

 whey which are detectable by the use of a simple chemical test. 



In addition to destroying disease-producing bacteria, pasteuri- 

 zation greatly improves the feeding value of whey by killing 

 yeasts and bacteria which produce undesirable changes in the 

 whey. Pasteurization prevents the separation and consequent 

 loss of butter fat, and saves a large part of the milk sugar that 

 is lost by souring in unpasteurized whey. There is a feeling that 

 pasteurization of whey improves the quality of cheese because the 

 patrons' cans are not seeded with undesirable bacteria when taking 

 whey back to the farm. At the places where pasteurization is in 

 use, neither the cheese men or the farmers would be willing to 

 discontinue the practice. 



Practically the entire bacterial flora of pasteurized whey was 

 found to consist of Bacillus hulgarlcus. This is the long 

 rod form of lactic acid organism. The ordinary sour milk bac- 

 teria are short rods or even spherical in shape. B. bulgaricus 

 develops in large numbers in the warm whey as it cools over night, 

 but never produces as much acid as it would if the whey were not 

 pasteurized. A single examination of unpasteurized whey from a 

 tank that had the appearance and odor of an old swill barrel 

 showed B. bulgaricus predominant, but mixed with a large num- 

 ber of yeasts and other organisms. This unpasteurized whey had 

 an acidity three times as great as that of pasteurized whey, and 

 the fat was all on the surface. The fat accumulated from day to 

 day and formed a dirty sour mass, which was never cleaned out of 

 the tank. Under such conditions the pasteurized whey has a 

 greater feeding value than unpasteurized whey. 



The results of this investigation indicate that the best way to 

 pasteurize whey is by introducing live steam directly into the 

 storage tank, either with or without the use of a steam jet pump 

 for drawing the whey from the vat. Four of the factories visited 

 were securing satisfactory pasteurization, and all four were using 

 direct steam in the tank. Double jetting can not be relied upon 



