42 BUTTER-MAKING. 



about 175° F. the properties of the enzyme are destroyed Owing 

 to this it is easy to detect whether a certain sample of milk has 

 been pasteurized or not. Galactase is present in so small a 

 quantity that it could not be determined in milk quantitatively. 

 It must be detected in a qualitative way. 



The test used and invented by Storch, of Copenhagen, 

 Denmark, is to put a small quantity of milk in a test-tube, add to 

 it a small quantity of a weak solution (2%) of hydrogen peroxide 

 (H2O2), a small quantity of potassium iodide, and a httle starch 

 solution. The whole mixture is then shaken. If the mixture does 

 not change in color, it has been heated to at least 170° F. If it 

 turns blue, it has not been heated to a sufficiently high tempera- 

 ture to destroy the properties of the enzyme present in the milk. 

 Another test which can be used in distinguishing raw milk from 

 scalded or boiled milk is to take 10 cubic centimeters of the milk 

 to be tested, add 1% of recently prepared aqueous solution of 

 "Ortol," and then one or two drops of hydrogen peroxide. If 

 the milk has not been heated, a vivid red color is produced. 

 Heated milk shows no effect. 



7. Divides the Fat-globules. — The fat-globules in normal 

 milk are grouped in minute clusters. When milk is heated, 

 these clusters break up, and each globule exists more or 

 less independently. When heated to an excessively high 

 temperature, and exposed to this temperature very long, the 

 fat-globules tend to run together. This can be proved by 

 heating milk in an open vat for about half an hour. A small 

 amount of yellow fat will then be seen floating on the top. 



8. Caramelizes the Sugar. — The brownish color which the 

 milk assumes when it is heated excessively is due to a change 

 which the milk-sugar undergoes. Fleischmann claims that the 

 sugar begins to change into a substance known as lacto-caramel 

 at a temperature of 160° F. This change, however, is not 

 pronounced enough to be apparent in the color, unless the milk 

 is heated a long time. The higher the temperature is, and the 

 longer it is exposed to the heat, the more pronounced is the 

 change. 



