106 MILK [vi 



Pasteurisation imparts to milk a slight taint of 

 the cooked flavour, but this flavour is removed on 

 the milk being cooled down. The maximum tem- 

 perature, therefore, to which milk may be submitted 

 in pasteurising should be below that which imparts 

 to the milk a permanent cooked flavour. Thus it 

 has been found that while heating the milk to a 

 temperature of about 65 C. (149 Fahr.) for twenty 

 minutes induces the flavour of cooked milk, this 

 flavour is not permanent, and quickly disappears on 

 cooling. According to Duclaux, milk suffers per- 

 manent change in taste when heated to 70 C. (158 

 Fahr.). This temperature, then, would seem to be 

 the limit to which milk should be heated in pasteur- 

 ising. Pasteurisation, however, merely temporarily 

 checks fermentation, since it does not kill all the 

 bacterial spores in the milk. The curdling of milk 

 which has been pasteurised is rather different in its 

 character from ordinary sour milk curdling, and is 

 brought about by bacteria, which are able to excrete 

 rennet. Lactic acid bacteria, as a rule, do not form 

 spores. 



For the above reasons intermittent sterilisation, 

 on theoretical grounds, is to be preferred to all 

 other methods. Unfortunately, however, it is such 

 an inconvenient method, and requires so much time, 

 and is so little suited for extended application, that 

 it cannot be carried out on a wholesale scale. At 



