A field test for titratable acidity and the determination of lactic acid by gas chromatography

A simple, convenient kit was developed to measure titratable acidity (TA) of milk in farm bulk tanks. The kit was based on the conventional determination of TA with standard base and phenolphthalein. Glass tubes were calibrated to contain a calculated amount of milk and base to show the phenolphthalein endpoint up to a chosen TA level. Samples remaining white would be rejected as TA above the chosen level. A survey using the kit and standard TA titration was carried out in winter and summer on manufacturing and Grade A milks. In 192 samples, TA averaged 0.164% and ranged from 0.11 to 0.31% TA with a standard deviation of 0.021% TA. There was no difference from grades or seasons. The kit test failed on only four samples. Lactic acid content of milk was measured in selected samples by an ether extraction-gas chromatographic method. Good agreement was obtained between the method and added and/or developed acidity determined by titration. Fresh milks with varying TA were shown to contain no lactic acid.