Stéphane Vidal

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.

Impact of Headspace Oxygen and Closure on Sulfur Dioxide, Color, and Hydrogen Sulfide Levels in a Riesling Wine

Following an experimental design replicating typical winery conditions, a Riesling wine was bottled with different headspace oxygen levels and sealed with either a coextruded closure or a screwcap to investigate the impact of headspace oxygen and closure oxygen transfer rate on wine evolution. Using luminescence technology, dissolved oxygen and headspace oxygen, as well as oxygen ingress through the closure, were monitored during 24 months of bottle storage. Under typical winery conditions, headspace oxygen introduced at bottling was found to be a major component of oxygen in bottled wine. Headspace oxygen at bottling influenced loss of sulfur dioxide during bottle storage, being the main cause of sulfur dioxide decline during the first four months after bottling in 375 mL bottles. The loss of sulfur dioxide was not correlated with the evolution of dissolved oxygen, but with the total amount of oxygen consumed by the wine. After 24 months in the bottle, color differences due to different headspace oxygen and closure oxygen transfer rate were generally minor. Conversely, differences in closure oxygen transfer rate were responsible for significant differences in the final concentration of the off-odor compound hydrogen sulfide, with screwcap generally associated with higher levels of this compound. Even if less significantly, the amount of oxygen present in the headspace at bottling also had an effect on final hydrogen sulfide, with higher concentrations observed in wines bottled with lower headspace oxygen.

Sulfur Dioxide – Oxygen Consumption Ratio Reveals Differences in Bottled Wine Oxidation

The availability of oxygen to a wine after bottling can have both beneficial and detrimental effects over time, which may be altered by the wine’s storage history. A Chardonnay wine underwent four different aging treatments: aged in stainless steel with and without lees and aged in oak barrels with and without lees. After six mos of aging, the wines were bottled and subjected to four levels of oxygen exposure by differences in bottle closure. The wines were then monitored for dissolved, headspace, and total consumed oxygen (TCO) concentrations, SO2, aldehydes, esters, and many other standard endpoints. After bottling with substantial oxygen uptake, oxygen consumption was slow, with 0.5 mg/L dissolved oxygen persisting in some bottles after six mos. SO2 concentration decreased and absorbance at 420 nm increased in response to higher accumulated oxygen exposure, expressed as TCO. A comparison of oxygen versus SO2 consumed by the wine provided new insights into the development of oxidation products. Wines aged on yeast lees consumed more SO2 for each equivalent of oxygen consumed. As these wines also had lower levels of weak SO2-binding agents, we hypothesized that these agents interfered in SO2-mediated protection against wine oxidation. At 12 mos after bottling and using descriptive analysis, the 16 wines were rated for 13 attributes determined by 14 judges in triplicate. The aging container, consisting of either stainless steel or oak barrels, had the largest impact on the descriptive analysis followed by oxygen availability through the bottle closure. Wines with the highest TCO had noticeably oxidized characters. The ratio of SO2 versus O2 consumed may help identify wines that will become oxidized. SO2-binding agents and their role in affecting wine oxidation and SO2 analysis needs clarification.

Impact of Dissolved Oxygen at Bottling on Sulfur Dioxide and Sensory Properties of a Riesling Wine

A Riesling wine was bottled with different levels of dissolved oxygen and sealed with two different coextruded closures and one screwcap closure in order to investigate the impact of dissolved oxygen and of closure oxygen transfer rate on wine evolution. Dissolved oxygen introduced at bottling influenced sulfur dioxide decline during bottle storage, especially during the first three months. However, the loss of sulfur dioxide was more strongly correlated with the total amount of oxygen consumed by the wine rather than with the evolution of dissolved oxygen. Closure oxygen transfer rate also influenced sulfur dioxide loss, and this effect became greater with time in the bottle. Although closure was an important factor influencing sensory attributes of bottled wine, within each closure, dissolved oxygen accounted for significant differences across the wines. Wines bottled with high dissolved oxygen showed significantly higher ratings for oxidation, confirming the influence of dissolved oxygen management on the evolution of wine over time.