The influence of Cu fractions in wine on sulfur dioxide to oxygen consumption ratios

Abstract

Sulfur dioxide is the most commonly used preservative for protecting wine against oxygen, whereby two molecules of total sulfur dioxide are consumed for each molecular of oxygen. Ascorbic acid can be added to white wines to assist sulfur dioxide in its antioxidant role, and can decrease the total sulfur dioxide consumed per molecule of oxygen to near 1:1. Increases in Cu concentration are well known to accelerate the reactions between oxygen and wine components, but the impact of the different Cu binding agents commonly found in wine on the total sulfur dioxide to oxygen consumption ratios is not certain. For this study, a white wine, white wine with ascorbic acid and red wine were each adjusted to three different Cu binding profiles via the addition of variable amounts of hydrogen sulfide. The Cu binding profiles of the wine were measured by bicinchonic acid that could distinguish Cu bound to either organic acids, certain thiol compounds or sulfide. After the treated wines were saturated with oxygen, the oxygen concentration, free and total sulfur dioxide and Cu binding profiles were measured periodically during storage of the wines at 17 °C. For the white wines with ascorbic acid, the rate of oxygen consumption was highly sensitive to the Cu binding profile, being accelerated by increased Cu organic acid concentrations. However, the Cu binding profile had no influence on the mole consumption ratio for total sulfur dioxide to molecular oxygen, or ascorbic acid to molecular oxygen, which was 1:1 for both sets of consumption reactions. For the red and white wines, without ascorbic acid, there was no significant difference in oxygen consumption rate or total sulfur dioxide to oxygen consumption ratios with the different Cu binding profiles. The latter consumption ratio was close to 2:1 for white wine and 1.5:1 for red wine. Therefore, the Cu binding profile did not influence the total sulfur dioxide to oxygen mole consumption ratios in any wines, and only impacted to oxygen consumption rate in white wines containing ascorbic acid.

References

Waterhouse, A.L., Frost, S., Ugliano, M., Cantu, A.R., Currie, B.L., Anderson, M., Chassy, A.W., Vidal, S., Diéval, J-B., Aagaard, O. and Heymann, H. (2016). Sulfur dioxide – oxygen consumption ratio reveals differences in bottled wine oxidation. Am J Enol Vitic. 16006.