Postmodern Winemaking: Rethinking the Modern Science of an Ancient Craft

by Clark Smith

Here’s something weird. Above 3.6, KHTa precipitation lowers TA and raises pH, just as you’d expect. Below 3.6, however, TA is lowered, but so is pH. The acid goes down, but it also goes up. Softer taste, but more stability and freshness. Not too shabby. Because of this effect, it is often possible to deacidify low-pH wines by adding potassium carbonate (K2CO3). This is always Plan A. Here’s how it works. First, as the compound dissolves, it ionizes into potassium cations and carbonate anions: K2CO3 → 2K+ + CO32− Next, the carbonate neutralizes some protons, benignly turning that nasty acid taste into carbon dioxide bubbles and water: CO32− + 2H+ → H2O (water) + CO2 (bubbles) Since it removes free protons, this reaction does raise the pH; but the K+ ions will also enhance bitartrate precipitation, and as long as this happens below pH 3.6, this precipitation will lower both TA and pH, moving us back in the direction of the original low pH. A wine with a TA of 10 g/L and a pH of 3.1 can emerge with a TA of 7.5 g/L and a pH of 3.3 at negligible cost. Hot stuff, but only if we begin from a low pH starting point.