264 LIME AND MILK. 



basic lime salts present, forming acid lime salts. When no more 

 basic salts are available for the neutralisation of acid, then only 

 the lactic acid will attack the orthocasein. 



The casein molecule is " double potential " i.e., it contains 

 a basic and an anhydric nucleus and we must assume that the 

 molecular structure is such that these nuclei have no opportunity 

 of mutual neutralisation. Therefore casein can combine with 

 a base and form a salt. Possibly the explanation is that on 

 contact with a base the casein is dissociated in such a manner 

 that the anhydric nucleus obtains liberty of action, whereas on 

 the other hand contact with an acid liberates the basic principle. 



In cheese-making we are striving to regulate the formation of 

 a salt by casein and acid, hence it is important that no such for- 

 mation takes place before the milk is submitted to the special 

 process, or at least that such formation be kept within certain 

 limits. 



Professor Lloyd has drawn attention to the fact that a certain 

 proportionate relation seems to exist between lime, casein, and lactic 

 acid and that a deficiency in one substance is usually accom- 

 panied by a deficiency in the other substance. This matter 

 wants further elucidation. A proportion between " acid," 

 as found by means of the acidimeter, and casein is very probable, 

 as casein has. an " acid value " and certainly affects the soda 

 solution used in the determination. A proportion between casein 

 and lime, again, is probable, as the casein in the milk is bound 

 to lime. But the exact relation between the three bodies is not 

 yet sufficiently clear. 



The quantities of lactic acid present in milk depend on quantities 

 and species of bacteria present, temperature, quantity of milk 

 sugar, and the time that has elapsed since drawing. Probably 

 a certain " balance " in the composition of milk will eventually 

 be found. 



When we introduce rennet into milk, the role of the lime changes. 

 The active principle of rennet, a chymosine, affects the colloidal 

 and suspended proteid, but leaves the dissolved proteid untouched. 

 The ferment changes the ortho-casein into para-casein, but there 

 its action stops ; it produces no actual coagulation. As soon 

 however as the para-casein comes into contact with soluble lime 

 salts a coagulum is formed. This w^as proved by Hammersten 

 with artificial milk, containing no lime. The introduction of 

 rennet produced no visible change, but the para-casein was preci- 

 pitated at once on the subsequent introduction of a lime salt. 

 This explains why matured or ripened milk will coagulate more 

 readily than absolutely fresh milk, for ripened milk will contain 

 more soluble lime salts than fresh milk. On the other hand 

 " ripened " milk will give a reduced yield in curds as a greater 

 proportion of proteid will be in a dissolved state, due directly 

 or indirectly to biological action and consequently escape the 

 action of chymosine. 



The effect of a shortage in lime salts becomes apparent at once. 

 In curdling, the rennet will change the ortho-casein into para- 

 casein, but in case of a shortage in soluble lime salt, part of the 



