136 MODERN METHODS OF TESTING MILK 



DETECTION OF SKIMMED MILK 



The percentage of fat in milk in relation to the 

 other milk-solids is reduced either ( i ) by direct re- 

 moval of fat through some process of skimming or 

 (2) by the addition of separator skim-milk to nor- 

 mal milk. ]\Iilk containing less than 3 per cent, of 

 fat is generally skimmed. Watering milk does not 

 disturb the relations of the constituents of milk to 

 one another, since it reduces the percentages of all 

 uniformly, but the removal of fat does very seriously 

 afifect the amounts of the constituents in respect to 

 their relative percentages. In skimming milk, the 

 solid constituent most largely removed is fat, com- 

 paratively little casein, sugar, etc., being taken with 

 the fat. The removal of fat therefore leaves the milk 

 containing less fat but with most of its casein, sugar, 

 etc., still remaining. In normal herd milk, containing 

 over 3 per cent, of fat, the percentage of fat is rarely 

 as low as the percentage of casein and albumin. In 

 5,500 analyses of samples of American milks, compiled 

 by the author, with a fat content l}ing between 3 and 

 5 per cent., the fat averages 3.92 per cent., and the ca- 

 sein and albumin together, 3.20 per cent. ; that is, for i 

 part of casein and albumin there is an average of 

 1.225 parts of fat. In skimming such milk, the fat may 

 be decreased to i per cent, or .1 per cent., but the re- 

 maining milk still contains about 3.20 per cent, of 

 casein and albumin. Milk is open to the suspicion of 

 being skimmed, when the percentage of fat falls be- 

 low that of the casein and albumin. 



The percentage of fat removed, based on the legal 



