David Carter, Carmen Vavra, Alexander Gapinski, Yiliang Cheng, and Aude Watrelot*
*Iowa State University, Department of Food Science and Human Nutrition, 536 Farm House Lane, Ames, IA, 50011 (watrelot@iastate.edu)

Sulfur dioxide is the most widely used preservative in wine to protect against microbial spoilage and oxidation. In red wines, phenolic compounds such as anthocyanins and tannins are extracted from grapes during the first days of alcoholic fermentation and are responsible for color stability, mouthfeel, and protection against oxidation. This study aimed to evaluate the evolution of quality in red wine made from the cold-hardy interspecific grape cultivars Marquette and Frontenac during aging. Wines of varying vintages from 2013 to 2020 provided by Iowa wineries with basic chemistry at bottling were chemically characterized. The pH, titratable acidity, color intensity, hue, phenolics, and tannin concentrations were quantified in triplicate using UV-vis spectrophotometry and HPLC-DAD, respectively. The amount of free and total SO2 in the aged bottles was quantified by titration and compared with the amount of SO2 added at bottling. The basic chemical parameters such as pH and titratable acidity were not impacted by aging time. Total phenolic concentration was the highest in 2013 wines. Tannin concentrations were <500 mg/L for all wines and vintages, reducing the level of protection against oxidation. The older the wines, the higher the hue of Frontenac wines, suggesting some oxidative browning in old Frontenac wines. However, aging time did not affect the hue of Marquette wines. As expected, the amount of free SO2 after aging was less than at bottling, but there was no difference in SO2 loss between cultivars. These results suggest that the color of Frontenac wines is less stable than that of Marquette wines during aging, probably due to a different ratio of tannins to anthocyanins. Ongoing research is currently focusing on red wine quality made from cold-hardy red grape cultivars after addition of three SO2 concentrations at bottling.

Funding Support: USDA-AMS Specialty Crop Block Grant Program (SCBGP).