254 UNSWEETENED ConpbENSED Mik Drrecis 
mer and Hart,’ and by Rogers*® show that the titratable acidity 
of fresh milk is not the only, and often not the really important 
factor, controlling the coagulation of milk, but that the stability 
of the casein, or its resistance to the coagulating effect of ex- 
posure to heat, depends on the relation of certain ash constit- 
uents. 
Sommer and Hart conclude that maximum stability of the 
casein demands a proper balance of calcium and magnesium with 
the phosphates and citrates, while the sodium and potassium 
chlorides in the concentrations present do not have any marked 
influence on the coagulating point. Thus these investigators state, 
the coagulation of milk on heating may be due either to an excess 
or a deficiency of calcium and magnesium. ‘The calcium in the 
milk distributes itself between the casein, citrates, and phos- 
phates chiefly. “If the milk is high in citrate and phosphate 
contents, more calcium is necessary in order that the casein 
may retain its optimum calcium content after competing with 
the citrates and phosphates. Jf the milk is high in calcium, 
there may not be sufficient citrate and phosphate to compete 
with the casein to lower its calcium content to the optimum. 
In such a case the addition of citrates or phosphates makes the 
casein more stable by reducing its calcium content. The magne- 
sium functions by replacing the calcium in the citrates and 
phosphates. 
“Tn most cases the coagulation is due to an excess of caleium 
and magnesium. It is possible to balance this excess by citrates, 
phosphates, carbonates and other salts.". See also Chapter XT 
on “Sterilizing,” Mojonmer Viscosity Controller. 
The factors of relation of ash constituents are influenced 
and largely controlled by such conditions as breed, period of 
lactation, health and feed of the cows. And this fact in turn 
may be accepted to explain, why there is a vast difference in 
the abilitv of milk produced in different localities, to withstand 
different degrees of concentration and_ sterilization without 
developing a permanent and objectionable curd. It is a well 
1H. H. Sommer and £. B. Hart, The Heat Coagulation of Milk, Jour. 
Biol. Chemistry, Vol. XL, No. 1, 1919. 
27L. A. Rogers, Address, Milk Section National Canners’ Association, 
Cleveland, O., 1920. 
