THE CHEMISTRY OF COOKERY. 497 



form, as the curd of new milk, it carries with it the fatty matter, or 

 cream, and therefore, in order to study its properties in a state of 

 purity, we must obtain it otherwise. This may be done by allowing 

 the fat-globules of the milk to float to the surface, and then remove 

 them i. e., by separating the cream as by the ordinary dairy method. 

 We thus obtain in the skimmed milk a solution of casein, but there 

 still remains some of the fat. This may be removed by evaporating 

 it down to solidity, and then dissolving out the fat by means of ether, 

 which leaves the soluble casein behind. The adhering ether being 

 evaporated, we have a fairly pure specimen of casein in its original or 

 soluble form. 



This, when dry, is an amber-colored, translucent substance, devoid 

 of odor, and insipid. This insipidity and absence of odor of the pure 

 and separated casein is noteworthy, as it is evidently the condition in 

 which it exists in milk, but very different from that of the casein of 

 cheese. My object in pointing this out is to show that in the course 

 of the manufacture of cheese new properties are developed. Skim 

 milk a solution of casein is tasteless and inodorous, while cheese, 

 whether made from skimmed or whole milk, has a very decided flavor 

 and odor. 



If we now add some of our dry casein to water, it dissolves, form- 

 ing a yellowish, viscid fluid, which, on evaporation, becomes covered 

 with a slight film of insoluble casein, which may be readily drawn off. 

 Some of my readers will recognize in this description the resemblance 

 of a now well-known domestic preparation of soluble casein, condensed 

 milk, where it is mixed with much cream, and in the ordinary prepara- 

 tion also much sugar. The cream dilutes the yellowness, but does not 

 quite mask it, and the viscidity is shown by the strings which follow 

 the spoon when a spoonful is lifted. If a concentrated solution of 

 pure casein is exposed to the air it rapidly putrefies, and passes 

 through a series of changes that I must not tarry to describe, be- 

 yond stating that ammonia is given off, and some crystalline sub- 

 stances, such as leucine, tyrosine, etc., very interesting to the physio- 

 logical chemist, but not important in the kitchen, are formed. 



A solution of casein in water is not coagulated by boiling ; it may 

 be repeatedly evaporated to dryness and redissolved. Upon this de- 

 pends the practicability of preserving milk by evaporating it down, 

 or " condensing." This condensed milk, however, loses a little ; its 

 albumen is sacrificed, as everybody will understand who has dipped a 

 spoon in freshly-boiled milk and observed the skin which the spoon 

 removes from the surface. This is coagulated albumen. 



If alcohol is added to a concentrated solution of casein in water, a 

 pseudo-coagulation occurs ; the casein is precipitated as a white sub- 

 stance like coagulated albumen, but, if only a little alcohol is used, the 

 solid may be redissolved in water ; if, however, it is thus treated with 

 strong alcohol, the casein becomes difficult of solution, or even quite 

 vol. xxiv. 32 



