Relation between Titratable Acidity and Hydrogen Ion Concentration of Ice Cream Mixes

It has long been known that the titratable acidity of milk freshly drawn from the cow does not indicate the true acidity, and that the acidity as it then appears, when determined by means of the ordinary acid tests, is merely apparent acidity.Van Slyke and Bosworth (1) showed that this acidity is due to the presence of substances other than lactic acid in the milk.McIn'erney (2) noted that milk freshly drawn from the cow gave an acid reaction to titration with an alkali which he calls apparent acidity due to carbon dioxide, acid phosphates and casein.The apparent acidity was found to range between 0.10 and 0.22 per cent and milks high in milk solids-not-fat were found to be higher in apparent acidity than milks of lower milk solids-not-fat content.Rice and Markely (3) found the acidity of cow's milk, calculated as lactic acid, to vary from 0.086 to 0.229 per cent and the hydrogen ion content to vary from pH 6.3 to 7.2, with an average of pH 6.5.Sharp and MeInerney (4) obtained samples of milk which ranged in acidity from 0.05 to 0.50 per cent, calculated as lactic acid and in hydrogen ion concentration from pH 6.0 to 7.73.By plotting the titratable acidity of the samples against the pH values, they found that a definite relation existed, but that the relationship for fresh milk was different from that after lactic acid had formed in the milk due to the action of bacteria.