PASTEURIZED MILK. 



277 



such as cholera, typhoid, and tubercle bacilli, are killed. This, and 

 this alone, is what is effected by Pasteurizing, and should always be 

 effected by it. On this account, milk which has been so strongly 

 and so long heated that the above results have been safely obtained, 

 or milk in which the lasting forms, and the forms of such bacteria 

 as prefer unusually high temperatures can alone be present, is 

 named correctly Pasteurized milk. Correctly speaking, Pasteurized 

 milk is, for example, milk 

 which has been heated for 



15 minutes at 75 C. or for ^f 



30 minutes at 68 C. The 

 action effected by Pasteur- 

 izing is the more perfectly 

 brought about the more 

 carefully the operation is 

 carried out. If it be de- 

 sired to take every pos- 

 sible precaution, attention 

 must be paid to having 

 the milk contaminated 

 as little as possible in 

 the process of milking. 

 The Pasteurizing appar- 

 atus should be cleaned for 

 fifteen minutes before use, 

 and the cooling of the Pas- 

 teurized milk should be 

 carried out as quickly as 



possible in a cooler, which should also have been previously steamed. 

 The cooled milk should then be put in steamed vessels, and care 

 taken that it should not be left to stand for any time in uncovered 

 receptacles. Properly Pasteurized milk keeps at ordinary animal 

 heat for 20 to 24 hours at 20 C.; about 60 hours at 12 to 15 C.; 

 72 hours, and often even longer at lower temperatures, in a con- 

 dition which admits of its being boiled without coagulation. It 

 only possesses a flavour slightly suggestive of boiled milk, and may 

 be converted into cheese, since its susceptibility to rennet has only 

 been weakened to a very slight extent. In spontaneous coagu- 

 lation it forms a comparatively spongy coagulum. Occasionally it 

 is not lactic bacteria which induce, after a lapse of time, coagula- 



Fig. 78. Laval Milk Scalder. 



