Why are pH and Titratable Acidity (TA) not “proportional”?

By Charles Plant

In wine chemistry, pH and TA measurements operate independently because they measure different aspects of acidity. pH specifically quantifies “free” hydrogen ions present in the liquid, while TA measures the total acid content—both free and bound forms.

During TA measurement, sodium hydroxide is added to the must. Initially, it neutralizes the free hydrogens responsible for pH readings. However, as the process continues, additional sodium hydroxide “unhooks” bound hydrogen particles, converting them to free hydrogens. The measurement concludes only when “sufficient sodium hydroxide” has been added to release all accessible hydrogen ions.

The crucial factor explaining the lack of proportionality between these measurements is variability: “the proportions of free and bound hydrogens varies greatly according to grape varietal, ripeness, growing conditions and so on.” Consequently, two wines can exhibit identical pH levels while possessing different TA values, or vice versa.

This relationship demonstrates why winemakers cannot reliably predict one measurement from the other without direct chemical analysis.