296 Dr. Lyon Play fair on the Milk of the Cow. 



into alcohol, and the alcohol into acetic acid. These changes 

 are induced by a primary action of oxygen upon the casein. 

 This action is then imparted to the other constituents, the atoms 

 of which being once set in motion, readily undergo the changes 

 described. The acetic acid being formed by the agency of air 

 on the alcohol, acts upon the soluble casein and coagulates it, 

 or renders it insoluble. It is thus removed from the action of 

 the oxygen of the air, and may be kept for some time without 

 entering into putrefaction. Such are the changes which milk 

 undergoes in summer, but they are quite different in winter. 



In winter the first action is that of oxygen upon the casein. 

 The temperature is not sufficiently elevated to cause vinous 

 fermentation. The decay of the casein generally passes over 

 to putrefaction, that is, the atoms are transformed more rapidly 

 than they unite with oxygen. A putrid smell now arises. 



Good butter cannot be made from milk which has under- 

 gone this change. The cause is, that butter always contains 

 a certain quantity of casein which it is difficult to remove. 

 When incipient putrefaction has taken place, it cannot be 

 arrested by ordinary means, and imparts itself to the bodies 

 with which it is in contact. It is for this reason that the 

 greatest part of the butter manufactured in winter has a rank 

 putrid taste. 



The principal object in view in the preservation of milk in 

 winter, is to prevent the commencement of this putrefaction. 

 One method has been termed scalding the milk, and is gene- 

 rally used in dairies. It consists in heating the milk until the 

 oxygen of the air acts upon the casein, and forms a pellicle 

 on its surface. The milk should then be left to perfect repose. 

 The pellicle excludes the air from the soluble casein. The 

 partial oxidation by which the pellicle was produced, is ef- 

 fected at too high a temperature to enable the decay to pass 

 into putrefaction. When this operation is skilfully performed, 

 the milk remains quite good for four or five days. But 

 there is a risk of failure in this process, and it is only adapted 

 for small dairies. 



The best method, which I have seen used in practice with 

 much success, seems to be to induce the acetous fermentation 

 in the milk. For this purpose, the cream or milk, being 

 placed in a proper vessel, should be surrounded with hot 

 water. The heat which I find to answer best is from 100° 

 to 110°. A cloth may be thrown over the whole to retain the 

 heat, and as the water cools, it should be removed and reple- 

 nished with hot water of the above temperature. In a few 

 hours the cream acquires the smell and taste of vinegar. The 

 changes which I have described above ensue. In large dairies 



