Mariola Kwiatkowski

Evolution of 3-mercaptohexanol, hydrogen sulfide, and methyl mercaptan during bottle storage of Sauvignon blanc wines. Effect of glutathione, copper, oxygen exposure, and closure-derived oxygen.

The effects of wine composition and postbottling oxygen exposure on 3-mercaptohexanol (3-MH), hydrogen sulfide (H2S), and methyl mercaptan (MeSH) were investigated. A Sauvignon blanc wine with initial copper concentration of 0.1 mg/L was treated with copper sulfate and/or glutathione (GSH) prior to bottling to give final concentrations of 0.3 and 20 mg/L, respectively. The wines were bottled with a synthetic closure previously stored in either ambient air or nitrogen to study the effect of the oxygen normally present in the closure. Bottled wines were stored for 6 months in either air or nitrogen to study the effect of oxygen ingress through the closure. Copper addition resulted in a rapid initial decrease in 3-MH. During storage, a further decrease of 3-MH was observed, which was lower with GSH addition and lowered oxygen exposure. H2S accumulated largely during the second 3 months of bottle storage, with the highest concentrations attained in the wines treated with GSH and copper. Lower oxygen from and through the closure promoted H2S accumulation. The concentration of MeSH was virtually not affected by the experimental variables at 6 months, although differences were observed after 3 months of storage. The implications for wine quality are discussed.

Oxygen consumption and development of volatile sulfur compounds during bottle aging of two Shiraz wines. Influence of pre- and postbottling controlled oxygen exposure.

The evolution of different volatile sulfur compounds (VSCs) during bottle maturation of two Shiraz wines submitted to controlled oxygen exposure prior to bottling (through micro-oxygenation, MOX) and postbottling (through the closure) was investigated. H(2)S, methyl mercaptan (MeSH), and dimethyl sulfide (DMS) were found to increase during aging. Lower postbottling oxygen exposure, as obtained by different degrees of oxygen ingress through the closure, resulted in increased H(2)S and methyl mercaptan. In one wine MOX increased the concentration of H(2)S and methyl mercaptan during maturation. Dimethyl disulfide and DMS were not affected by any form of oxygen exposure. Overall, postbottling oxygen had a stronger influence than MOX on the evolution of VSCs. Data suggest that dimethyl disulfide was not a precursor to methyl mercaptan during bottle maturation. For the two wines studied, a consumption of oxygen of 5 mg/L over 12 months was the most effective oxygen exposure regimen to decrease accumulation of MeSH and H(2)S during bottle aging.