2i2 MILK AND DAIRY PRODUCTS PART 



As the anaerobic butyric acid bacteria are killed sooner than 

 the whey bacteria (peptonising bacteria) it is possible, as has 

 been shown above, to gain some idea as to the temperature to 

 which the pasteurisation has been carried by the changes which 

 take place when the milk is kept in the incubator. 



Perfectly sterile milk must naturally remain unchanged 

 when kept in the incubator at 35 to 40 C. 



II. BUDDISED MILK. 



In the examination of milk which has been treated with 

 hydrogen peroxide according to Budde's or any other method, 

 the two main points to be investigated are, firstly, whether unde- 

 composed hydrogen peroxide is present in the milk and in what 

 quantity, and, secondly, whether the milk is sterile or not. 



The milk should first be tasted, and if an excess of only 

 O05 g. hydrogen peroxide per litre is present a characteristic 

 taste may be detected. 1 When the quantity is less than this 

 the peculiar flavour is no longer noticed. As regards the 

 qualitative and quantitative detection of hydrogen peroxide in 

 milk, full details are given on p. 1*22. 



To prove the sterility of the milk it must be placed in a 

 closed flask in the incubator at a temperature of 35 to 40, just 

 as was done with milk sterilised by heat. If the milk is sterile 

 it should undergo no change, but if not, and the hydrogen 

 peroxide has only been used to make it more durable, then it 

 and a sample of normal milk should be kept for a few days 

 under the same conditions and tested for the degree of acidity 

 every few hours. 



Sometimes it happens that the acidity of the milk heated 

 with hydrogen peroxide only increases slightly, but an 

 objectionable smell and unpleasant taste are to be noticed. 

 This is caused by the lactic acid bacteria having been killed, 

 and the remaining putrefactive bacteria have gained the upper 

 hand. Such milk must naturally be rejected absolutely. It is 

 essential that the milk treated with hydrogen peroxide should 

 either be sterile or have been treated so little that the lactic 

 acid bacteria still predominates, and souring can take place in 

 the normal manner. 



1 Chr. Barthel, lleniK Mn. du Lait, Vol. II, p. 289. 



