396 THE KEEPING OF MILK. 



form. (Not more than 0-1 per cent, of albumin is found in steri- 

 lised milk in the soluble form.) The casein separates on acidifying 

 in a more finely divided state. 



If the milk has been heated to 100 C. or a higher temperature 

 for any length of time, the rotatory power of the milk- sugar 

 undergoes a serious reduction, the cupric reducing power not 

 changing to any appreciable extent. The milk also assumes a 

 slight brownish colour, due probably to the formation of a 

 " caramelised " body of low rotatory power. 



The cream rises with extreme slowness ; in three hours, prac- 

 tically no cream is observed on the surface of the milk ; and 

 after six hours, the layer is only about one-tenth of that given 

 by new milk. If sterilised milk be allowed to stand for twenty- 

 four hours or more the bulk of the cream will rise to the surface, 

 but the quantity will be less than that yielded by new milk ; 

 the cream will, however, contain a distinctly larger percentage 

 of fat, about 40 per cent., as against less than 30 per cent, in the 

 cream yielded by new milk. 



The diminished yield of cream is a property shared also by 

 milk which has been pasteurised by heating to about 70, but 

 the rate of rise of cream in pasteurised milk is fairly rapid ; 

 practically the same amounts are found in three hours as in six 

 hours. The total quantity of cream from pasteurised milk is 

 about half that of fresh milk. 



The figures in Tables CXXXIII. and CXXXIV., which were 

 obtained by Boseley and the author, will illustrate the above 

 facts. 



Table CXXXIV. showing the behaviour of new milk is produced 

 here for the sake of comparison. The samples 1 to 5 are from 

 the same cows respectively which yielded the samples with 

 corresponding numbers in the tables illustrating the behaviour 

 of sterilised milk. 



Condensed unsweetened milk, which has been diluted to the 

 original volume with water, has all the analytical characteristics 

 of sterilised milk. It throws up its cream rather less readily even 

 than sterilised milk. This is but slightly due to the fact that it 

 has been condensed, but is owing to the sterilising process that 

 it has undergone. No. 6 in Table CXXXIII. was diluted con- 

 densed milk. There appears to be no good method of dis- 

 criminating between condensed milk diluted with water and 

 sterilised milk. If a water containing large amounts of nitrates 

 has been used for diluting the condensed milk, a strong diphenyl- 

 amine reaction will indicate the probability that water has been 

 added ; this test is not of a sufficiently absolute character to be 

 relied on. This is to be regretted. The subject has been con- 

 sidered of sufficient importance by the British Dairy Farmers' 



