8 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE. 



most striking^ shown. One false step, such as running pasteurized 

 milk through a piece of dirty cheesecloth before it enters the bottle 

 filler, may undo all the previous work. Pasteurization is an added 

 expense, and merely as a matter of business, it is hard to believe that 

 after the process is properly performed anyone would willfully al- 

 low the results to be spoiled by a single operation, no matter whether 

 the object of the process is to produce a sanitary milk or merely 

 to preserve it. The failure of a few plants to pasteurize properly is 

 no reason for condemning the process. In such cases a little educa- 

 tion will often produce marked improvement and enable the milk 

 dealer to meet city regulations. 



The control of the process of pasteurization should be based only 

 on accurate scientific data. In the past it has often been the practice 

 to expect a bacterial reduction of 99 per cent during pasteurization. 

 While it is an easy matter to destroy 99 per cent of the bacteria when 

 the raw milk contains large numbers, it is often impossible, on ac- 

 count of heat-resistant bacteria which are not necessarily spore form- 

 ers, to destroy 99 per cent when the milk contains about 100,000 bac- 

 teria per cubic centimeter. In a large number of experiments in 

 which milk was pasteurized under exact laboratory conditions, where 

 no reinfection was possible, in one sample only 17 per cent of the 

 bacteria were destroyed. Often 99 per cent of the bacteria may be 

 destroyed, and yet the milk may still contain hundreds of thousands, 

 while in other cases in which it contains only tens of thousands, the 

 per cent of reduction may have been only from 80 to 90. The ef- 

 ficiency of the process can not be based on the per cent of bacteria 

 destroyed. 



In the control of pasteurization it is essential that the proper tem- 

 perature be used and that the process be so performed that no rein- 

 fection takes place. This can be accomplished best by direct super- 

 vision of milk plants by trained men who have authority to carry 

 on such supervision, and by bacteriological control of the process. 



HANDLING PASTEURIZED MILK. 



The pasteurization of milk destroys about 99 per cent of the bac- 

 teria; consequently the milk is not sterile. On account of this fact 

 pasteurized milk is still a perishable product, and must be handled 

 with the same care as raw milk. This is a point for both the con- 

 sumer and the milkman to remember. 



Milk after pasteurization should be cooled to about 40° F. and 

 kept at that temperature until delivery. During warm weather it 

 should be iced on the delivery wagons. From a sanitary standpoint 

 all milk, whether raw or pasteurized, should be delivered as soon as 

 possible, in order that the consumer may get it in the best condition. 



