264 CITY MILK SUPPLY 



completed. He found that by heating wine to temperatures ranging 

 from 122 to 140F. souring and other undesirable changes could be pre- 

 vented. The process has proved applicable to a variety of foods and 

 has been called in honor of the discoverer, pasteurization. It may be 

 denned as the process of checking or delaying bacterial decomposition 

 of food and other substances, by exposing them to heat in such a manner 

 as to effect a partial destruction of the contained germs, leaving alive 

 only those that are in the spore state and others that, though they sur- 

 vive, bring about changes in the substance but slowly or not at all. 

 Pasteurized foods will not keep indefinitely for usually some germs in 

 time attack them. Pasteurization is to be carefully distinguished from 

 sterilization by heat, for in the latter process such high temperatures are 

 used that both the germs and their spores are killed. Sterilization as a 

 means of preserving foods is severely limited, for the temperatures used 

 to effect it are so high that many foods are injured to such a degree as to 

 be unusable. 



Application of Pasteurization to Milk. The attempt was made to 

 sterilize milk for human consumption but it was found necessary to heat 

 it for a long time at 212F., or to higher temperature which gave the milk 

 a decided flavor, caramelized the milk sugar and otherwise radically 

 changed it so that the public would have none of it. Pasteurization has 

 proved applicable to milk and from being used only by physicians in a 

 limited way and for special purposes has been accepted by the public 

 and is practised commercially on a tremendous scale. 



Soxhlet in 1886 was the first to propose the use of heated milk in infant 

 feeding. In this country the first allusion to the subject, according to 

 Rosenau, was in 1889 by Jacobi who had long used heated milk in his 

 extensive practice as a pediatrician. The growth of the use of pasteurized 

 milk was gradual for practitioners raised objections to it and the public 

 was suspicious of it but it has overcome prejudice and established itself. 



Progress in the art of heating milk also was slow, for many difficul- 

 ties were encountered but they have been surmounted. Three principal 

 methods of pasteurization have been perfected, namely: (1) the flash, 

 instantaneous or continuous; (2) the holder, holding, held or discontinuous; 

 and (3) in the bottle or in final-package, processes. In the flash method 

 milk is exposed for from a few seconds to perhaps 3 min. at temperatures 

 of from 175 to 185F., while in the holder method temperatures of from 

 140 to 150F. are used and the exposure is usually for 20 to 45 min. 

 The bottle or final-package method may be regarded as a modification 

 of the holder process and the temperatures and times of heating are about 

 the same. The bottling of milk hot which has been proposed by Ayres 

 and Johnson amounts to a variation of the bottle method and is in the 

 experimental stage. 



The dairy industry has adopted pasteurization in the manufacture of 



