Robert Coleman,* Roger Boulton, and Alexei Stuchebrukhov
*University of California, Davis, 1 Shields Avenue, Davis, CA 95616 (bcoleman@ucdavis.edu)

Existing descriptions of the oxidation reactions in wine are independent of pH and the tartaric acid concentration. The iron-mediated catalysis of dioxygen to form reactive oxygen species constitutes the initiation step in the oxidation of wine. Over a broader pH range than that of wine, from pH 2.5 to 4.5, the speciation of Fe(II) and Fe(III) and their complexes change dramatically, therefore changing the rate at which these oxidation reactions can occur. In this experimental study, air-saturated model wine solutions of Fe(II) and tartaric acid were followed for the rates of oxygen consumption and Fe(III) formation. Attempts to measure hydrogen peroxide formation were also employed to assist in the elucidation of the auto-oxidation nature of the kinetics. The auto-oxidation lag time and extent of oxygen consumption was pH dependent, while the maximum rate of oxygen consumption was pH independent. Additionally, the lag time, maximum rate of oxygen consumption, and extent of oxygen consumption were probed by adding varying amounts of reactants (Fe(II), tartaric acid), intermediates (hydrogen peroxide), and intermediate-scavenging agents (Cu(II), catalase, superoxide dismutase). Future work will attempt to express these oxidation curves using a pH- and metal speciation-based model.

Funding Support: Stephen Sinclair Scott Endowment in Viticulture and Enology, Wine Spectator Fellowship, Treasury Wine Estates