CHAPTER TTT 

 THE ANALYSIS OF MILK-PRODUCTS 



THE liquid milk-products are skim-milk, cream, whey, 

 butter-milk, sterilised milk, condensed milk, and sour or 

 fermented milk ; milk powder consists of milk evapo- 

 rated to dryness. 



Skim-milk is treated exactly as milk ; as the fat 

 globules are very small and few, the estimation of fat 

 requires more care ; the period of revolution of the disc 

 in the Gerber method should be increased, and a cor- 

 rection of 0.05 per cent, should be added to the reading 

 unless a special tube is used. The gravimetric methods 

 of Storch and Ritthausen tend to give slightly low 

 results, and those of Werner- Schmid or Gottlieb are 

 preferable. In the estimation of the proteins by 

 Ritthausen's method, the extraction of the fat may be 

 omitted, and the percentage of fat found subtracted 

 from the results. 



Cream requires several modifications. The specific 

 gravity, except of a thin cream, is difficult to estimate, 

 and this is usually omitted. It is advantageous to ad<T 

 an equal volume of alcohol to the cream before drying 

 for the total solid estimation, as there is then no skin to 

 be broken. The fat may be estimated by macerating 

 the total solids with ether or amyl alcohol, carefully 

 decanting and repeating the maceration, &c., about 

 half a dozen times ; the solids not fat are weighed 

 directly, and the fat found by difference. The ash 

 estimation is made on the solids not fat. The Werner- 

 Schmid method is, however, excellent for cream, with the 

 modification that 2 or 3 grammes should be weighed, into 

 the Stokes tube, and the weight made up to 10 grammes 

 with water. The Gottlieb method is also good ; i to 2 

 grammes should be weighed, and enough water added 



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