Dr. Lyon Play fair on the Milk of the Cow. 297 



a portion of this soured cream or milk maybe added to fresh 

 cream or milk, which should be kept in a room possessing a 

 temperature of 60°. By adding this soured cream to the 

 fresh milk, we furnish an acid, by which the sugar of milk is 

 converted into grape sugar. The curd then acts upon the 

 grape sugar, and converts it into alcohol. The latter by oxi- 

 dation becomes acetic acid, and thus the whole mass of milk 

 is rendered sour, the casein coagulated, and therefore pro- 

 tected from immediate putrefaction. The butter made from 

 such soured milk is quite sweet and destitute of that rank 

 taste which distinguishes our winter from summer butter. 

 But if incipient putrefaction has once begun in the milk, all 

 this will be of no avail, because it is communicated to the in- 

 soluble casein. Milk perfectly fresh must therefore be used. 

 Fresh milk soured in this way will last for many days, and 

 give risings of cream for a considerable time. This practice, 

 as far as I am aware, is not a general one, though it is well 

 worthy of adoption. In summer of course no such operation 

 is requisite, as it is done at a sacrifice of the skimmed milk. 

 One great cause of the putrefaction in milk is the want of 

 absolute cleanliness in the dairy. If a drop of milk fall on 

 the table, it should be dried and washed off with care, for its 

 putrefaction causes the evolution of a putrid gas, and this im- 

 parts its state of putrefaction to the remainder of the milk. 



With respect to making butter, scientific explanations can 

 be of little use to practical men. The theory of churning is 

 very simple. By agitation, the globules of butter are broken, 

 and made to unite together into a mass. The introduction of 

 air during churning, aided by the heat at which the cream or 

 milk is, occasions the formation of lactic or acetic acid, and 

 this coagulates the casein, and thus assists the separation of 

 the butter. In summer, when the heat prevents the ready co- 

 herence of the butter, a quantity of cold spring water thrown 

 in, after the butter-milk has formed, often effects the desired 

 end. The temperature is thus depressed, the butter rendered 

 solid and more coherent, while the air contained in the water 

 aids in the formation of acid and coagulation of the casein. 

 The only thing, in a scientific point of view, to attend to after 

 the separation of the butter, is to free it from butter-milk or 

 casein. If the casein be suffered to remain, putrefaction en- 

 sues, and the butter acquires a rank putrid taste. Its sepa- 

 ration is therefore of the first moment. 



The cause of the superiority of certain foreign butter, which 

 retains its flavour and taste for a considerable time, is more 

 due to its freedom from casein than to any mystery in its mode 

 of preparation. 



