STATUS OF PASTEURIZATION OF MILK. 21 



was based on experiments in which milk was heated to temperatures 

 near the boiling point and can not be applied to milk pasteurized at 

 low temperatures. From the results of many years' work in the 

 Dairy Division on commercial pasteurized milk, it has been found 

 that such milk sours, as raw milk does, but that the souring is 

 delayed when compared with the souring of the same grade of raw 

 milk. Pasteurized milk sours in a manner similar to that of a high 

 grade of raw milk, and there is no more reason to fear the over- 

 growth of putrefactive organisms than there is in any high-grade 

 milk. Pasteurization for 30 minutes at temperatures of about 145 

 F., as is generally practiced in this country, does not destroy all 

 the lactic-acid organisms, and those which survive play an important 

 role in the souring of commercially pasteurized milk. 



Another objection to pasteurized milk has been that bacteria grow 

 faster in it than in raw milk. In spite of several experiments which 

 seem to prove this point, it has never been thoroughly established. 

 It has been found that the rate of bacterial increase is approximately 

 the same when the comparison is made between raw milk and pasteur- 

 ized milk having about the same bacterial content. 



It is often stated that pasteurization, even if it does destroy 

 bacteria, does not destroy poisonous products of their growth. This 

 can hardly be considered a real objection, for if they are present in 

 raw milk they must be consumed with it, and if pasteurization does 

 not destroy them the pasteurized milk would be no worse than raw 

 milk. 



The question as to whether pasteurization destroys beneficial 

 enzyms is still an open one. In the light of our present knowledge 

 of the enzyms in milk and the part they play in the digestive process 

 it is quite impossible to settle the question of their importance. It 

 is evident, however, that the low temperatures now in use in pasteuri- 

 zation have little effect on the commonly recognized enzyms. 



The opponents of pasteurization have raised an objection on the 

 ground of its direct influence on the milk producer. It has been 

 asserted that pasteurization would cause lax methods of production 

 on the farm, for the reason that farmers would know that the milk 

 was to be pasteurized and, therefore, they could be careless in its pro- 

 duction. There seems to be some basis for this objection, but in any 

 city where there is any inspection of the raw-milk supply the same 

 inspection can and should be continued even though the milk is to 

 be pasteurized. 



From a chemical standpoint ^serious objections have been raised 

 against pasteurized milk, because the heating produces changes which 

 render the milk less digestible, particularly in the case of infants. 

 As has already been stated, however, Rupp (26) has found that milk 



