Joy Ting,* Kirsty Harmon, and Matthieu Finot
*Winemakers Research Exchange, 325 Winding River Lane, Suite 202, Charlottesville, VA, 22911 (vawrex@gmail.com)

Cabernet franc and Petit Verdot are the two most-widely planted red grape varieties in Virginia. Despite characteristics that produce good quality fruit and distinctive wines, high fruit potassium (K) often leads to wines with high pH. A common winemaking approach to rectify high pH is through relatively large tartaric acid additions, but winemakers differ in when these additions are made. Prefermentation additions are often recommended; however, this approach lacks guidelines to determine how much acid to add to achieve a target pH without adverse sensory consequences. In 2020 and 2021, the Virginia Winemakers Research Exchange tested the chemical and sensory effects of adding relatively large amounts of tartaric acid at fruit processing compared to post-malolactic additions. Initially, additions were done based on prior experience, resulting at times in over-addition and wines with high sensory scores for acidity. In the second year, measurement of juice K prior to inoculation was used to estimate the final wine pH. Using published data from other regions and historic data sets from Virginia, ranges of K (low, medium, high, very high) were defined and tartaric additions were done according to where juice values fell within those ranges. As expected, juice K was a better predictor of wine pH than juice pH. Measuring juice K avoided over-acidulation in all trial wines. Wines with prefermentation acid additions had lower volatile acidity and were scored as more “fresh” than wines with postfermentation additions. Based on this approach, assessing juice K prior to inoculation may be a practical strategy to inform the magnitude of prefermentation acid additions and avoid the adverse sensory effects of over-addition.

Funding Support: Virginia Wine Board