Gordon Walker, James Nelson, Desmon Hernandez, Thomas Halligan, Andre Knoesen, and Ron Runnebaum*
*UC Davis, 1 Shields Avenue, Davis, CA 95616 (rcrunnebaum@ucdavis.edu)

As part of a larger effort to characterize site-specific contributions in Pinot noir wines, four sites were selected to examine the relationship between vineyard, must composition, and fermentation dynamics. These vineyards were selected for their replicable fermentation kinetics and consistent organoleptic properties. The wines were produced from the same clone of Pinot noir and were made using the same enological process. To gain insight into real-time dynamics of fermentation, oxidation reduction potential (ORP) probes were used to measure redox potential during alcoholic fermentation. Redox potential determines the type and frequency of chemical half-reactions in solution, including speciation and reactivity of metals. ORP is a quantifiable metric that responds to changes in pH, temperature, dissolved oxygen, enzymatic activity, and yeast metabolism in real time. ORP probes are standard for anaerobic fermentation industries but are not widely used for wine. For a comprehensive view of the characteristics of these wines, phenolics extraction and elemental composition were also analyzed. The vineyards were selected to represent faster- and slower-fermenting musts. While vintage variation exists, these sites have displayed robust trends over five years of vinification. The working hypothesis was that placing ORP probes into the replicate fermentations would provide insight into yeast metabolic activity and determine differences in kinetics. The observed fermentation profiles matched previous vintages, consistent with our expectations. We also observed typical differences in phenolics, anthocyanin extraction, and the elemental profile among wines (specifically the Fe:Mn ratio). The ORP profiles followed similar trends for all fermentations, a sign that the temperature-based process control worked effectively. By examining the ORP profiles in detail, deviations in ORP revealed previously undetectable differences between sites and replicates. ORP is exquisitely responsive to small perturbations, making it ideal to use a process parameter for monitoring and controlling fermentations.

Funding Support: Jackson Family Wines, Silver Oak Cellars, WineXRay