Maisa Martins Monteiro Lima,* Desmon Hernandez, Taylor Reiter, Ben Montpetit, and Ron C. Runnebaum
*UC DAVIS, 3127 RMI North Viticulture & Enology, Davis, CA 95616 (mmlima@ucdavis.edu)

The conversion of malic acid to lactic acid is responsible for deacidification, flavor modifications, and microbial stability of wines. The presence of lactic acid in wines is generally through malolactic fermentation (MLF). Lactic acid can also be formed by the presence of microorganisms on grapes or in the winery. The presence of lactic acid in juice at the beginning of fermentation has been shown to have an effect on fermentation outcomes in non-wine fermentations. Gene expression data of Pinot noir wines has shown instances of fermentation outcomes that are consistent with the presence of lactic acid in early fermentation from select vineyards. To better understand the presence and reproducibility across vintages of lactic acid in juice, three vintages (2017 to 2019) of Pinot noir wines from 15 vineyard sites were evaluated. Pinot noir grapes harvested represented eight American Viticultural Areas along the United States West Coast. The wines were produced with a goal of minimizing potential sources of variation, including using a single scion clone of Pinot noir and reproducible and replicated winemaking. Grapes were destemmed and inoculated with Saccharomyces cerevisiae RC212 yeast. MLF was completed by inoculation of Oenococcus oeni and the wines were stored in stainless steel vessels until bottling. Malic acid in juices was characterized by enzymatic assay prior. Lactic acid in wines was characterized using high-performance liquid chromatography. Wines from specific vineyard sites had more lactic acid concentration than possible after MLF on the basis of initial malic acid concentration (actual and theorical difference in lactic acid concentrations). Such differences suggest that significant levels of lactic acid were present prior to start of fermentation at these sites. These chemical composition results will be compared and contrasted with RC212 gene expression data from those same sites during primary fermentation.

Funding Support: Jackson Family Wines