Loss and formation of malodorous volatile sulfhydryl compounds during wine storage

Abstract

Volatile sulfur compounds (VSCs), particularly low molecular weight sulfhydryls like hydrogen sulfide (HS) and methanethiol (MeSH), are often observed in wines with sulfurous off-aromas. Recent work has shown both HS 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.

Copper(II) and Sulfur Dioxide in Chardonnay Juice and Shiraz Must: Impact on Volatile Aroma Compounds and Cu Forms in Wine

“…However, the measured bound Cu showed no decrease with Cu treatments from post-fermentation (PAF) to 15 months of aging (15Mo) ( Table 2). Hence, the apparent decrease in H 2 S concentration may have been due to an incomplete dissociation of the copper sulfide complexes during quantification [48]. Again, in contrast to the Chardonnay wines, the elevated SO 2 concentration in the grape must significantly (p ≤ 0.05) increased the H 2 S concentration in the Shiraz wines ( Figure 1B).…”

“…As bentonite removes proteins, which may act as a potential source for sulfide in wine, this may explain why significantly (p ≤ 0.05) lower H2S concentrations were measured in It is interesting that the decrease in bound Cu (i.e., sulfide bound) with bentonite treatments (Table 1) did not show equivalent decreases in H 2 S ( Figure 1A). The lack of change in H 2 S concentrations with bentonite treatments may be due to the incomplete dissociation of all bound sulfide from Cu during the LMWSCs quantification [48]. After 15 months of bottle aging (15Mo), the Cu addition treatments had significantly (p ≤ 0.05) increased H 2 S concentrations in the Chardonnay wines.…”

“…The exception is hydrogen sulfide/sulfide, for which the pretreatment is regarded as being insufficient to release all sulfide from metal complexes, particularly Cu. In this instance, the measured sulfide concentration represents the sulfide in wine that is not bound to metals and sulfide that can be released from metal complexes based on the pretreatment [48].…”

Recent Developments on the Origin and Nature of Reductive Sulfurous Off-Odours in Wine

“…Reductive off-odor problems are mostly caused by volatile sulfur compounds (VSCs) and equal to cork taint are responsible for an important proportion (30%) of faulty wines [1]. H 2 S is the most frequently found of these compounds, followed by methanethiol (MeSH) and ethanethiol (EtSH) [2]. Hydrogen sulfide can be generated by Saccharomyces cerevisiae in the course of sulfur assimilation during fermentation.…”

“…Numerous literature reports on the increases of free H 2 S and MeSH during wine storage have been published. A survey is given in [2].…”