Relationship between Titratable Acidity and pH during Lactic Acid Fermentation in Reconstituted Nonfat Milk

Summary Titratable acidity and pH measurements were made during lactic acid fermentation in reconstituted nonfat milk ranging from 9 to 20% solids. Measurements were made on the reconstituted products and also on the corresponding whey obtained therefrom. The results, which are presented in graphic form, show the relationship of the titratable acidity, pH, and solids concentration during fermentation down to pH 4.4. Before fermentation, an initial apparent acidity of 0.16% in nonfat milk containing 9% solids increased 0.02% acidity for each additional 1% increase in solids reconstituted, accompanied by a slight decrease in pH from 6.6 to 6.4. During lactic acid fermentation proportionately greater increases in titratable acidities of both the reconstituted products and whey were observed for each additional 1% solids increase. At pH 4.6 both the reconstituted solids and whey showed a 0.06% increase in titratable acidity for each 1% increase in the original solids concentration. Good quality cultured buttermilk was obtained, using reconstituted nonfat milk containing 11% solids and developing the titratable acidity to 0.90-0.95% at pH 4.5 to 4.4. Using the short-time method, satisfactory cottage cheese was obtained using nonfat milk containing 13% solids, cutting the curd at a clear whey titratable acidity of 0.62% at approximately pH 4.8, and permitting additional acid development to a final pH of 4.7 to 4.6.