The Role of Polyphenols in the Behavior of Potassium Bitartrate in Red Wines

Abstract

The role of polyphenols in the behavior of potassium bitartrate was studied both in red wines and in model solutions. Tannins alone had little effect in preventing the precipitation of potassium bitartrate from a decolorized wine or a model solution. A grape-skin extract, containing both pigments and tannins and the usual assortment of other cations and anions, markedly increased the solubility of potassium bitartrate in both decolorized wines and model solutions. The extract remaining after dialysis was also effective in decolorized wine, though not in a model solution, suggesting the dialyzable electrolytes as required cofactors of the pigments. Red wines were found to complex tartrate and not potassium. Part of the tartaric acid is so strongly complexed that it is unavailable for precipitation reactions, with another portion held in a series of complexes that break up at a decreasing rate over a long period. Wines differed greatly in complexing power. Evidence is presented indicating that surface adsorption on pigments rather than occlusion is responsible for the coprecipitation with potassium.