Technical Yearbook 2024

Conclusion A recent study confirmed the important role of sulphur dioxide (specifically molecular sulphur dioxide) in hydrogen sulphide production in wines packaged in lined aluminium cans. Results also showed that the potential formation of hydrogen sulphide is best predicted by molecular sulphur dioxide. Based on the results obtained in this study, the authors recommend a maximum molecular sulphur dioxide of 0.4 mg/L. This recommendation is based on the targeted shelf life of approximately six months at room temperature. This limit will likely have to be decreased if longer shelf lives are desired, or higher storage temperatures are expected.  This study confirmed that the likely explanation for the higher hydrogen sulphide formation observed in many canned wines is the reaction of sulphur dioxide and aluminium to yield hydrogen sulphide. Therefore, the fact that there is hydrogen sulphide formation would suggest that the sulphur dioxide gets into direct contact with the aluminium. This would suggest that the liner was breached in some way. The mechanism through which liner failure occurs is unclear 2,3 and may involve subsequent steps of liner degradation followed by a reaction of sulphur dioxide with the aluminium metal. Results showed that, for the epoxy liners, the wine component best correlated with hydrogen sulphide formation was molecular sulphur dioxide, followed by pH and free sulphur dioxide. However, because molecular sulphur dioxide is proportional to free sulphur dioxide, it is unclear whether the observed increase in hydrogen sulphide is due to molecular sulphur dioxide or to a synergistic interaction between free sulphur dioxide and pH. No correlation was observed between total sulphur dioxide and hydrogen sulphide production, indicating that bound sulphur dioxide is not involved in hydrogen sulphide formation. The red wines included in the study showed the lowest increase in hydrogen sulphide concentrations during storage. These two wines also had the lowest molecular sulphur dioxide of all those tested, mainly due to their relatively higher pH values. Thus, red wines are expected to be relatively low in concern for hydrogen sulphide formation during storage. Liner failure

analysed only at the end of the storage period (eight months). Results Hydrogen sulphide increases during storage in bisphenol A (BPA)-epoxy-lined cans • After two months’ storage: Relatively small increases in hydrogen sulphide were detected in three white wines. At this point, the hydrogen sulphide concentrations were still mostly below 10 μg/L. • After four months’ storage: Most white and rosé wines showed some increases in hydrogen sulphide. However, only three wines reached hydrogen sulphide levels above 10 μg/L. • After eight months’ storage: Further increases were observed, with six white and rosé wines having a hydrogen sulphide concentration of more than 10 μg/L. • Negligible hydrogen sulphide production was observed for the two red wines and most control samples, which were packaged in glass bottles. The role of the can liners • Hydrogen sulphide formation following eight months of storage in cans lined with BPA epoxy and BPA-non intent (NI) epoxy correlated well. The preferential use of these two liners is unclear and would likely depend on the specific composition of the liner. • Wines stored in acrylic-lined cans showed highly degraded liners and extreme hydrogen sulphide production after only two months. This liner is not recommended for the canning of wines. Visible liner damage Damage was measured by visual assessment of the inner surfaces of the cans, which took the form of small blisters. Similar to the hydrogen sulphide production, liner damage was not detected for most of the wines until after four months of storage. After eight months, the extent of liner damage correlated well with hydrogen sulphide formation. Correlation between wine components and hydrogen sulphide formation The study’s researchers evaluated different wine components to ascertain if a correlation between specific wine constituents and hydrogen sulphide formation exists. The evaluated parameters included free sulphur dioxide, total sulphur dioxide, molecular sulphur dioxide, pH, alcohol content and titratable acidity.

References https://www.wineland.co.za/hydrogen-sulphide-formation-in-canned-wines/

For more information, contact Carien Coetzee at carien@basicwine.co.za.

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TECHNICAL YEARBOOK 2024