ADULTERATIONS OF MILK 221 



genizing machine are exceedingly small, and microscopic examina- 

 tion readily reveals this condition. Furthermore, the small glob- 

 ules resulting from the homogenizing process do not rise readily, 

 and the absence of a cream line indicates that the milk has been 

 tampered with. 



Foreign fats may be discovered by chemical methods, but 

 these are laborious, time consuming, and not always reliable. 



Coloring-matter in Milk 



Coloring-matter is sometimes added to milk to impart a rich 

 appearance, especially after it has been either skimmed or watered. 

 Then, too, when milk is derived from animals producing milk 

 poor in fat, artificial color is added to increase its attractiveness. 

 Annatto, caramel, and anilin dyes are chiefly used for this pur- 

 pose. While annatto and caramel are harmless, the azo-dyes may 

 be poisonous, as arsenic, copper, tin, lead, and zinc may be intro- 

 duced during manufacture. A general indication of the presence 

 of caramel or azo-dyes can be had by coagulating the casein with 

 rennet extract or acid. In pure milk the pigment (carotin, 

 xanthophyll) is contained in the fat, and therefore the curd of 

 pure milk is white, while the curd of milk colored with caramel 

 or some azo-dye has the characteristic color of the dye used. 

 Annatto is taken up by the fat and the curd remains white. 



Another indication of the presence of caramel or some azo- 

 dye is the color of the skimmed milk after the cream has risen. 



The use of caramel or annatto does not injure the wholesome- 

 ness of the milk, but there is no advantage in their use unless the 

 milk has been tampered with or is of poor quality. 



Artificial coloring of milk can be detected by the following 

 tests (Leach's method): Warm about 150 c.c. of the milk to be 

 tested in a casserole over the flame and add about 5 c.c. of acetic 

 acid, after which slowly continue the heating nearly to the boil- 

 ing-point, stirring all the while. Gather the curd, when possible, 

 into one mass by the use of the stirring rod, and pour off the whey. 

 If the curd breaks up into small flakes, separate from the whey 

 by straining through a sieve or colander. Press the curd free 

 from adhering liquid, transfer to a small flask, and macerate for 

 several hours (preferably over night) in about 50 c.c. of ether, 

 the flask being tightly corked and shaken at intervals. 



Detection of Annatto. — Decant the ether extract as obtained 

 above into an evaporating dish, place on the water-bath, and 

 evaporate the ether. Make the fatty residue alkaline with 

 sodium hydroxid, and pour upon a very small wet filter while 

 still warm. After the solution has passed through, wash the fat 



