210 MILK AND DAIRY PRODUCTS PART 



has naturally diminished owing to the dilution. The whey, 

 which is used for the preparation of milk sugar, is generally 

 evaporated, after the precipitation of any nitrogenous sub- 

 stances which may be present, in a vacuum pan, and the crude 

 milk sugar allowed to crystallise out. It is then purified 

 according to various methods, decolorised, refined, etc., so that 

 the final product is quite colourless. 



EXAMINATION OF PRESERVED MILK AND OTHER 

 MILK PREPARATIONS. 



I. STERILISED AND PASTEURISED MILK. 



The chemical analysis of sterilised and pasteurised milk is 

 naturally performed in exactly the same manner as in the 

 case of milk alone. Preparations of this sort ought not to 

 have a brownish-yellow colour, nor ought the fat globules 

 have run together so that the drops are visible to the naked 

 eye. Neither ought it to be dificult to get the layer of 

 fat which forms in the bottles to mix again with the milk. 

 When homogenised milk is being dealt with the fat cannot 

 be estimated by any of the extraction methods, owing to the 

 reason given on page 51, for these all give results which are 

 too low, sometimes as much as 0'5 per cent. The Rose-Gottlieb 

 method is, however, quite satisfactory, for the fine state of 

 division of the fat particles in the emulsified milk has no effect 

 upon the result. Gerber's method also gives good results if the 

 samples are whirled for a considerably longer time than usual. 

 Should the centrifuge not be one that can be heated, then the 

 samples must be warmed and whirled several times until no 

 more fat separates. The degree of acidity of pasteurised milk 

 is often somewhat lower than that of the unheated milk, owing 

 to a loss of free carbon dioxide during heating. S torch's test 

 (p. 98) will show whether the milk has been heated to more 

 than 80 C., but there is no means of learning definitely how 

 far the heating has exceeded this temperature. By means of 

 the so-called Schardinger reaction 1 it is possible to get a good 

 idea of the temperature to which the milk has been heated, and 

 also the length of time. Schardinger found that when a certain 



1 See Buttenberg, Zeitschrift f. Unt. der Nahr.- n. Genussmiitel,- 1906, 

 Vol. II, p. 377. 



