The reactions of (+)-catechin and (')-epicatechin with glyoxylic acid were studied in a model white wine solution. When the reactions were performed in darkness at 45 °C, the (')-epicatechin concentration decreased more rapidly than that of (+)-catechin, and the (')-epicatechin sample had twice the 440 nm absorbance of the (+)-catechin sample after the 14 day incubation period. The main pigments generated were identified as xanthylium cation pigments regardless of the isomeric character of the phenolic compound. Using a combination of absorbance and ion current data, the xanthylium cation pigments generated from (')-epicatechin were found to have combined molar absorptivity coefficients 1.8 times that of the xanthylium cation pigments generated from (+)-catechin. The implication of these results on the development of an index of white wine oxidation susceptibility is discussed.