530 MILK 



the organisms of other cattle diseases, and may serve to spread 

 these diseases. Furthermore, dairy products are frequently in- 

 jured or may have to be rejected on account of the activity of 

 micro-organisms which cause abnormal fermentation. These or- 

 ganisms are also spread frequently through skimmed milk and 

 whey. 



Skimmed milk and whey should always be pasteurized before 

 they are delivered to patrons of creameries or cheese factories. 

 Dotterer and Breed and Farrington and Hastings recommend 

 flash pasteurization at 176° F. for these products. In Denmark 

 and several states of this country legislation has made pasteuriza- 

 tion of skimmed milk and whey compulsory. 



Tests. — Hastings recommends two tests for the proper pas- 

 teurization of skimmed milk and whey, namely, the Storch test 

 and the potassium-iodid-starch test. According to this author 

 the tests are carried out as follows : Starch's test: Two solutions are 

 prepared: 1. Dilute 1 part commercial hydrogen peroxid with 

 14 parts water. This solution keeps for about six weeks. 2. 

 One part paraphenylendiamin is dissolved in 50 parts water and 

 the solution filtered. To 20 c.c. of the milk in a teacup are added 

 3 to 5 drops of Solution 1, and after mixing, 1 to 2 drops of Solu- 

 tion 2. A grayish-blue color develops at once in raw milk, while 

 in milk heated to 176° F. or above no color appears immediately. 

 Some color may appear in two minutes or after a longer interval. 

 One per cent, raw milk in heated milk can be detected by this 

 test. 



The potassium-iodid-starch test is preferred to the Storch test 

 by Hastings, because the material can be readily purchased. 

 Two solutions are necessary for this test, namely: 1, The potas- 

 sium-iodid-starch solution, and 2, diluted hydrogen peroxid. The 

 first solution is prepared as follows: Mix 2 to 3 parts of wheat 

 starch with a little cold water and then pour 100 parts boiling 

 water on it. Stir well. Then add 2 to 3 parts potassiiun iodid, 

 previously dissolved in a little water. For the test, place 20 to 

 30 c.c. of the milk in a teacup and mix with it 15 to 20 drops of 

 Solution 1. Then add 6 to 8 drops of Solution 2. In raw nulk a 

 blue color appears immediately around the hydrogen peroxid, or 

 sometimes the color is greenish when an insufficient quantity of 

 potassium-iodid-starch solution is present. Any color develop- 

 ing later may be disregarded. 



The critical temperature of both tests is 176° F. If the milk 

 has been heated to this temperature or higher, no color develops, 

 but if heated to a temperature between 160° and 174° F., the color 

 appears more slowly than in raw milk. 



There have been a number of objections raised to pasteuriza- 



