While regulations for making organic wine in the United States prohibit addition of sulfite during processing, they do not disallow the presence of sulfite. Certain wine strains of Saccharomyces cerevisiae produce relatively high levels of sulfite (>10 ppm). This production is a result of natural metabolic processes that yeast share with other microbes and plants; specifically, synthesis of the sulfur-containing amino acids methionine and cysteine. We are evaluating the factors that control high-sulfite production to determine strain suitability for production of organic white wines that do not undergo malolactic fermentation or aging, e.g., Pinot gris. The relationship between high-sulfite production and high sulfide formation in these strains has not been examined systematically under vinification conditions. Initially, we assessed commercial wine strains for both sulfite and sulfide production. A handful of high-sulfite producers were selected for further analysis. Spores of the high sulfite-producing strains were crossed to a low sulfite-producing laboratory strain and are currently being subjected to genetic analysis. Specifically, a rapid, high-throughput sulfite assay suitable for microtiter plate analysis was developed to follow this trait among hybrid progeny. A diagnostic medium is being used to follow hydrogen sulfide production. Two strains containing the previously characterized low-sulfide MET10-932 allele were found to produce high levels of sulfite and were confirmed to produce no sulfide. In contrast, another strain co-produced high levels of both sulfite and sulfide. These findings indicate that the relationship between high-sulfite production and undesirable high-sulfide formation varies among strains.

Funding Support: USDA-ARS