254 UNSWEETENED CONDENSED MILK DEFECTS 



mer and Hart, 1 and by Rogers 2 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. If the milk is high in calcium, 

 there may not be sufficient citrate and prjosphate 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. 



"In most cases the coagulation is due to an excess of calcium 

 and magnesium. It is possible to balance this excess by citrates, 

 phosphates, carbonates and other salts." See also Chapter XI 

 on "Sterilizing," Mojonnier 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 ability 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 



1 H. H. Sommer and E. B. Hart, The Heat Coagulation of Milk, Jour. 

 Biol. Chemistry, Vol. XL, No. 1, 1919. 



2 L. A. Rogers, Address, Milk Section National Canners' Association, 

 Cleveland, O., 1920. 



