Myths and Facts about the Role of Precursors in the Formation of “Reductive Aromas” in Wines Postbottling
Marlize Bekker,* Eric Wilkes, and Paul Smith
*The Australian Wine Research Institute, PO Box 197, Glen Osmond, SA 5064, Australia (email@example.com)
Volatile sulfur compounds (VSCs) are important wine compounds that impart “reductive” aromas that negatively impact wine aroma and quality. Hydrogen sul-fide (H2S) and methanethiol (MeSH) are two of the main compounds associated with “reductive” aromas in wines postbottling. Precursors previously suggested as playing important roles in modulating VSC concentrations in wines postbot-tling were evaluated. The ability of sulfur-containing amino acids such as cysteine (Cys), methionine (Met), and glutathione (GSH) and other low-molecular-mass sulfur compounds to act as precursors to H2S and MeSH were assessed in real wines. Cys and GSH did not act as precursors to H2S on a wine-relevant scale. The presence of copper remained the main factor that contributed to significant increases in H2S concentrations from yet-to-be-identified precursor compounds. Cys and GSH were associated with reduced H2S formation from copper-catalyzed reactions in Shiraz wines, either by inhibiting H2S formation from copper-catalyzed reactions or possibly by forming mixed disulfides through the reaction of Cys/GSH with H2S. Only dimethyldisulfide (DMDS) and methylthioacetate (MeSAc) contributed significantly and on a wine-relevant scale to MeSH con-centrations in wines postbottling. In all instances, the presence of copper had significant effects on the ability of precursors to produce H2S and MeSH and on the rate of H2S and MeSH formation. Wine pH also significantly affected MeSH formation. This study demonstrated that Cys, Met, and GSH do not pose a risk of H2S or MeSH formation in wines postbottling. However, the presence of Me-SAc, or a disulfide such as DMDS, posed a significant risk of MeSH formation, with up to a 20% MeSH yield and a 70% MeSH yield obtained from MeSAc and DMDS, respectively, in wines over a twelve-month storage period.
Funding Support: Australia’s grapegrowers and winemakers through their investment body, Wine Australia, with matching funds from the Australian Government