182 THE BOOK OF BUTTER 



at 6° C. (43° F.). In each case the salt concentration of 

 the medium on which the organisms were studied was 

 12 per cent. This calls attention to the effect of both low 

 temperature and the quantity of salt. It should also 

 be noted that 68° F. is about room heat and that the 

 temperature of the refrigerator maj^ rise quickly to that 

 of the room if great care is not observed. 



For long periods of storage, the temperature must be 

 many degrees lower than may be sufficient for short 

 periods. According to Gray and McKay/ butter kept 

 slightly better at - 10° F. than at 10° F. There was a 

 marked difference in favor of these lower temperatures 

 over the higher one, which was 32° F. The table on page 



183 from Rogers, Thompson, and Keithley ^ shows the ad- 

 vantage of temperatures near 0° F. for storing butter over 

 those a few degrees higher. 



The average number of points that the butter deteri- 

 orated at 0° F., 10° F., and 20° F., was 1.92, 2.99, and 

 3.59 respectively. It is apparent that low temperatures 

 are essential in good refrigeration. This table also calls 

 attention to the advantage of pasteurization and to the 

 use of unripened cream in butter-making. The following 

 statement of Rahn, Brown, and Smith ' concerning the 

 growth of micro-organisms at low temperatures bears 

 out the data in the above table on scores of butter at 



' Gray, C. E., and McKay, G. L., The Keeping Qualities 

 of Butter Made Under Different Conditions and Stored at 

 Different Temperatures, U. S. Dept. of Agri., B. A. I., Bui. 84, 

 p. 22, 1906. 



2 Rogers, L. A., Thompson, S. C, and Keithley, J. I., The 

 Manufacture of Butter for Storage, U. S. Dept. of Agri., B. A. I., 

 Bui. 148, p. 25, 1912. 



' Rahn, Otto, Brown, C. W., and Smith, L. M., Keeping 

 Qualities of Butter, Mich. Agri. Col. Exp. Sta., Tech. Bui. 2, 

 p. 43, 1909. 



