214 MILK 



DETECTION OF WATERED MILK, SKIMMED MILK, OR BOTH 

 WATERED AND SKIMMED MILK 



The addition of water involves dilution of the product and the 

 danger of introducing germs with polluted water. It is conceiv- 

 able, and actually has happened, that water containing pathogenic 

 bacteria has been added to the milk or has been used for washing 

 utensils which held milk. The addition of skimmed milk is of 

 relatively small sanitary importance, but it cheapens the product. 



When skimmed, milk has a higher specific gravity, and when 

 diluted with water the normal specific gravity is restored. The 

 solids, however, are reduced, and by determining the solids the 

 condition of tampered milk is revealed. The specific gravity 

 increases about 0.001 for each per cent, of fat removed, and de- 

 creases 0.003 for each 10 per cent, of water added. Each 10 per 

 cent, of water reduces the solids about 1.2 per cent., as shown in 

 the following table (Sommerfeld) : 



THE REDUCTION OF TOTAL SOLIDS WITH ADDITION OF WATER 



Per cent, water added 10 20 30 40 50 



Per cent, solids ....................... 12.0 10.8 9.6 8.4 7.2 6.0 



Per cent, water ....................... 88.0 89.2 90.4 91.6 92.8 94.0 



The addition of water also raises the freezing-point, lowers the 

 index of refraction, and reduces the viscosity. 



Skimmed milk is sometimes added to whole milk to increase 

 the producer's profits. The chief difference between milk that 

 has been watered and milk that has been skimmed or milk to which 

 skimmed milk has been added is that in the first instance the 

 relation of milk constituents remains the same, while in the other 

 cases the proportion of the constituents is seriously disturbed. 

 But while skimmed milk or milk diluted with skimmed milk re- 

 tains the solids in approximately their natural proportion with 

 the exception of the fat, watered milk contains the solids in re- 

 duced quantity. Van Slyke gives the following formula for cal- 

 culating the amount of fat in milk mixed with skimmed milk: 



F V 100 

 Per cent, of fat removed = 100 - 



F. represents the percentage of fat determined in the suspected 

 milk and the divisor 3 means that the original milk contained 

 3 per cent. fat. Since whole milk usually contains a greater 

 amount of fat than 3 per cent., the above formula gives results 

 more or less below the real amount of fat removed. 



Watering of milk can be detected by various methods. If 

 but small amounts of water are added, its presence may escape 

 discovery, and any quantity of water below 10 per cent, may be 



