PHYSICAL AND CHEMICAL EXAMINATION OF MILK 211 



They are then immersed in water at a temperature of 38 to 39 C. 

 (100 to 102 F.). By giving the jars an occasional rotary motion 

 the temperature soon rises, and when the thermometer shows that 

 the milk has reached 37 C. (98 F.) 10 drops of rennet extract 

 are added to each jar. The thermometer used to determine the 

 temperature of the milk must be scalded for each jar so as to avoid 

 infecting one sample of milk from another. After the milk has 

 coagulated it is allowed to stand for about twenty minutes. The 

 curd is now firm, and is cut with a knife, which must be sterilized 

 for each jar. The whey is liberated and the curd settles rapidly. 

 The sample is then tested with the senses and the whey poured off. 

 Additional whey that separates within the succeeding six to twelve 

 hours is poured off at intervals. Finally, after the last whey has 

 been removed, the curd is tested. It is cut into pieces and, if 

 normal, should be firm and free from holes. A spongy consistency 

 indicates activity of gas-producing organisms, chiefly of the 

 Bacillus coli and B. aerogenes type. When gas is formed the curd 

 is filled with small holes, "pin-holes, * and forms the so-called 

 "floating" or "gassy" curd. The odor of the curd may betray the 

 presence of undesirable organisms which, while they do not pro- 

 duce gas, may impart an unpleasant flavor to the cheese. 



Gerber's fermentation test was designed for a purpose similar 

 to that of the Wisconsin curd tekt. For making this test the 

 milk is placed in tubes, heated for six hours at 40 to 41 C. (104- 

 106 F.), and then the taste, odor, and general appearance ob- 

 observed. The milk is again heated for six hours at the same 

 temperature. If it coagulates during the second heating period, 

 it is considered abnormal. 



BIBLIOGRAPHY 



Ayers and Johnson: United States Dept. of Agri., Bull. 202, May, 1915. 



Babcock: Univ. of Wis. Agri. Exp. Sta., Bull. 24, July, 1890. 



Babcock and Farrington: Univ. of Wis. Agri. Exper. Sta., Bull. 195, February, 

 1910. 



Baer: Univ. of Wis. Agri. Exper. Sta., Circular of Information 41, September, 

 1912. 



Baer: Univ. of Wis. Agri. Exper. Sta., Bull. 241, July, 1914. 



Benkendorf, Bruhn, Baer, and Sammis: Univ. of Wis. Agri. Exper. Sta., 

 Bull. 241, July, 1914. 



Decker: Univ. of Wis. Agri. Exp. Sta., 16th Annual Report, 1899, p. 155. 



Farrington: Univ. of Wis. Agri. Exper. Sta., Bull. 129, September, 1905. 



Farrington and Woll: Testing Milk and Milk Products. 



Fleischmann: Lehrbuch der Milchwirtschaft. 



Hart: Univ. of Wis. Agri. Exper. Sta., Bull. 156, November, 1907. 



Hart, Suzuki, and Sammis: Univ. of Wis. Agri. Exper. Sta., Research Bull. 

 10, May, 1910. 



Hastings and Evans: United States Dept. of Agri., B. A. I., Circular 210, 

 April 10, 1913. 



Heinemann: Reprint from the Transactions of the 15th international Con- 

 gress of Hygiene and Dermography. 



