Kirsty Harmon and Joy Ting*
*Virginia Winemakers Research Exchange, P.O. Box 555, Ivy, VA 22945 (VaWrex@gmail.com)

Despite all that is known about the chemistry of SO2 in wine, many questions about its practical use remain. This study explored the effects of the concentration and timing of SO2 additions at the end of malolactic fermentation in Cabernet franc and Cabernet Sauvignon produced in the Monticello AVA of Virginia. In 2018, wine from a single lot of Cabernet franc was racked after completion of malolactic fermentation, then transferred to three sets of barrels (one set of comparable new barrels, two sets of comparable older barrels). One barrel from each set received 30 mg/L SO2 (“low dose”) while the other received 75 mg/L SO2 (“high dose”). In each pair, the wine receiving the higher dose maintained free SO2 levels at or near the target of 0.5 mg/L molecular SO2. Wines given the lower initial dose required many subsequent small additions of SO2 over five months to reach the same target. The high-dose wines had higher concentration of anthocyanins at the end of five months, with no differences in polymeric anthocyanins or tannins. In year two, the effect of “high” (75 mg/L) and “very high” (100 mg/L) doses of SO2 were tested in Cabernet Sauvignon. Wine receiving the “very high” dose maintained free SO2 levels above the 0.5 mg/L target for molecular sulfur throughout aging, with no need for additional doses. Modified sensory analysis by an untrained panel of 23 winemakers found the wines were significantly different in a triangle test, with significantly higher descriptive scores for aromatic intensity in the “very high” dose wine. Adding a larger initial dose of SO2 better maintains molecular SO2 levels associated with wine protection than many smaller doses toward the same target.

Funding Support: The Virginia Wine Board