Loss and formation of malodorous volatile sulfhydryl compounds during wine storage

ABSTRACT

Volatile sulfur compounds (VSCs), particularly low molecular weight sulfhydryls like hydrogen sulfide (H₂S) and methanethiol (MeSH), are often observed in wines with sulfurous off-aromas. Recent work has shown both H₂S and MeSH can increase up to a few µM (> 40 µg/L) during anoxic storage, but the identity of the latent sources of these sulfhydryls is still disputed. This review critically evaluates the latent precursors and pathways likely to be responsible for the loss and formation of these sulfhydryls during wine storage based on the existing enology literature as well as studies from food chemistry, geochemistry, biochemistry, and synthetic chemistry. We propose that three precursor classes have sufficient concentration and metastability to serve as latent sulfhydryl precursors in wine: 1) transition metal-sulfhydryl complexes, particularly those formed following Cu(II) addition, which are released under anoxic conditions through an unknown mechanism; 2) asymmetric disulfides, polysulfanes, and (di)organopolysulfanes formed through transition-metal mediated oxidation (e.g., Cu(II)) of sulfhydryls or pesticide degradation, and released through sulfitolysis, metal-catalyzed thiol-disulfide exchange or related reactions; 3) S-alkylthioacetates, primarily formed during fermentation, and releasable hydrolytically. Some evidence also exists for S-amino acids serving as precursors. Based on these findings, we propose a “decision tree” approach to choosing appropriate strategies for managing wines with sulfurous off-aromas.

KEYWORDS:

• Sulfur-like off-aromas
• reduced wines
• wine storage
• latent sulfhydryl precursors

Disclosure of interests

GYK, RJE, GLS, DWJ have no financial interests or benefits to disclose.

Additional information

Funding

This work was supported by the Australian Government as a part of the Australian Research Council's Industrial Transformation Research Program under Project IC130100005; USDA National Institute of Food and Hatch Appropriations under Project PEN04565 and Accession 1002916; USDA Northeast Sustainable Agriculture Research and Extension (NE-SARE) Graduate Program under Award GNE14-082; and the Pennsylvania Department of Agriculture and the Pennsylvania Wine Marketing and Research Board under Grant 44155243.