PART IV PRESERVED MILK AND OTHER 

 MILK PREPARATIONS 



INTRODUCTORY. 



UNDER the heading of preserved milk may be classed certain 

 preparations of milk which are prepared so as to enable the 

 milk to be kept for a longer time than would be otherwise 

 possible. 



These different preparations contain the whole of the 

 constituents of milk, but sometimes substances are added to 

 increase the keeping properties. In some cases the preserved 

 milk contains all the water normally present in milk, whilst in 

 other cases it is partially or almost entirely driven off. 



The usual preparations of preserved milk are sterilised milk 

 (pasteurised milk can to a certain extent be included), Buddised 

 milk, condensed milk, dried milk or milk powder (also milk 

 tablets). 



By sterilised milk is understood milk which, by heating, has 

 been completely freed from micro-organisms. It is, however, 

 difficult to obtain absolutely sterile milk, for various spore- 

 forming bacteria have very resistant spores which are able to 

 withstand long-continued heating at fairly high temperatures. 

 If the milk is to be sterilised in one operation, it must be 

 heated (usually in hermetically closed glass bottles) by steam 

 under pressure in a strong- walled apparatus. Nevertheless, a 

 temperature of 120 C. for 2 hours is necessary if the milk is 

 to be rendered absolutely sterile, and if the temperature is only 

 about 100 C., a considerably longer time is required. The milk, 

 however, undergoes such great changes in taste, appearance, 

 and composition as to be unsuitable for food. In practice, 

 therefore, the heating is only for a shorter time and the 

 temperature is kept fairly low, say 20 minutes at 112 C. 

 Where the temperature only slightly exceeds 100 C., a longer 

 time is necessary. In this way the milk, apart from a boiled 



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