CHAPTER XIX 



ON THE METHODS COMMONLY USED IN THE HEATING OF MILK 



THE use of cows' milk as a food for children has involved much 

 discussion as to the best method of heating the milk. Different 

 methods have been used in several countries, and there has been 

 not only considerable difference of opinion as to the best method 

 to employ, but also some confusion has arisen from the casual 

 use of the same term to denote different methods of dealing with 

 the food. It would not seem to be of any particular interest to 

 endeavour to trace the origin of the divergence either in the practice 

 or the use of terms, and it will be simpler here to explain briefly the 

 present position and the practices which are very generally employed. 



It will be possible to consider the main forms of heated milk 

 which are used under the terms, pasteurised, boiled, sterilised, and 

 dried milk. 



Milk is heated for two purposes : (a) In order to destroy harmful 

 bacteria, and (b) in order to preserve the milk for a longer period 

 than would be the case if heat were not employed. In both cases 

 the use of heat is connected with the presence of bacteria, since in 

 the second case the milk is in danger of going sour owing to the 

 presence of these organisms. 



PASTEURISED MILK 



Pasteurisation of milk appears to have been introduced by 

 Soxhlet. The original term was used to denote a milk which 

 had been heated to a temperature below that of boiling-point and 

 which had been subsequently rapidly cooled. This general meaning 

 is for the most part still preserved. Great differences, however, 

 exist in regard to the method of carrying out the pasteurisation. 

 Some pasteurisation is carried out at a temperature of only 60 C. 

 (140 F.), and, on the other hand, it is not uncommon for the process 

 to be designated as pasteurisation when the milk is in effect raised 

 to a temperature approximately equal to the boiling-point of water 

 100 C. (212 F.). Moreover, the length of time which is occupied 



