Aubrey DuBois, Marlie Shelton, Michael Qian, and James Osborne*
*Oregon State University, 100 Wiegand Hall, Department of Food Science and Technology, Corvallis, OR 97331 (james.osborne@oregonstate.edu)

The volatile phenol precursors p-coumaric and ferulic acid, naturally present in grapes, are typically found as esters of tartaric acid (coutaric and fetaric acid, respectively). The esterified forms, often present in higher concentrations in wine than the free forms, can be hydrolyzed during the winemaking process. Brettanomyces bruxellensis can use the hydrolyzed, free form of these hydroxycinamic acid esters to create volatile phenols, but cannot degrade the esterified forms. Therefore, this study investigated factors that may impact the hydrolysis of esterified hydroxycinnamic acids during winemaking, including malolactic fermentation (MLF), wine pH, wine ethanol content, and wine storage temperature. Pinot noir wines were produced and MLF was conducted with either a cinnamoyl esterase-positive or cinnamoyl esterase-negative Oenococcus oeni strain. At the completion of MLF, there were significantly higher concentrations of p-coumaric acid in wines where MLF was performed by the cinnamoyl esterase (+) O. oeni strain than in wines where the cinnamoyl esterase (-) strain was used. Wines were then adjusted to two different pH values and two different ethanol concentrations, sterile-filtered, bottled, and stored at either 13 or 21°C. Wines were assessed for esterified and free hydroxycinnamic acids after 0, 30, 100, and 180 days in storage. The concentrations of esterified and free hydroxycinnamic acids remained constant throughout aging. Concentration differences seen at the end of MLF remained after aging 180 days, regardless of wine pH, ethanol, or temperature of storage. At the end of aging, wines were inoculated with B. bruxellensis, growth was monitored for sixty days, and the wines were assessed for volatile phenol concentrations.

Funding Support: Northwest Center for Small Fruits Research