Final Report – Funding Cycle 2023-2025 (Two years)
Principal Investigator: Hailan Piao, Washington State University, Richland
Co-PI: Thomas Henick-Kling, Thomas Collins, James Harbertson, WSU, Richland
Telephone: (509) 372-7665
Summary: This two-year project studied the combined effects of sulfur dioxide and pH on the survival of three key wine-associated microorganisms: Saccharomyces cerevisiae, Brettanomyces bruxellensis, and Oenococcus oeni. The project focused on the effects of sulfur dioxide under wine storage conditions, typical pH and alcohol content, and evaluated different sulfur dioxide concentrations and wine pH for their microbial viability over a four-day period. Both red and white wine matrices were studied.
Red wine – Cabernet Sauvignon trials showed a clear relationship between lower pH values and increased microbial suppression. At moderately acidic conditions of pH 3.6, even small sulfur dioxide additions of 25 mg/L led to susbstantial reduction in S. cerevisiae, whereas at higher pH of 4.0, the same dose was less effective. Most B. bruxellensis cells died rapidly regardless of dosage, indicating their high susceptibility. O. oeni was also highly sensitive, especially at low pH and high sulfur dioxide concentrations.
White wine – Chardonnay trials showed similar trends to red wine of smaller doses of sulfur dioxide needed for lower pH wines, although higher total sulfur dioxide additions were needed to reach effective molecular sulfur dioxide concentrations do to presumably binding with other wine constituents.
The study also compared two analytical methods for measuring free sulfur dioxide. Capillary electrophoresis provided more accurate detection of free sulfur dioxide. The Admeo Y15 analyzer tended to overestimate values by including the weakly bound sulfur dioxide forms, which may lead to larger sulfur dioxide additions than necessary in the winemaking process.
Overall, the findings emphasize the critical role of wine pH and precise sulfur dioxide management for microbial control and that lowering wine pH enhances the antimicrobial effectiveness of sulfur dioxide, enabling microbial suppression at lower sulfur dioxide additions.
Download the report above.