Abstract Description

With climate change, the frequency of wildfires has increased in wine-producing regions, including the South African winelands. Wildfires pose a double threat to an industry already under pressure: the direct burning of vineyards, and the indirect smoke exposure. Indeed, upon smoke exposure, the volatile phenols (VPs) arising from the burning of lignin within the surrounding vegetation, are absorbed by ripening grape berries where they are glycosylated to non-volatile precursors. During wine fermentation, microorganisms release the VPs, which impart an unpleasant smoky/burnt off-flavour to the wines. The most efficient solution implemented in wineries is the addition of activated charcoal that reduces the odorous fault but also diminishes the overall quality of the wine because of its lack of selectivity. Furthermore, while effective at removing free VPs, charcoal poorly removes glycosylated VPs, which can be slowly released chemically during wine ageing. In this context, this study screened and characterised the ability of a large set of diverse yeasts and bacteria to enhance the release of free VPs during fermentation to enhance their removal by charcoal. The data demonstrated that all yeast and bacterial species displayed glycosidase activity but to varying degrees. Surprisingly, strains of the main wine yeast Saccharomyces cerevisiae, which reputedly display low glycosidase activity in wine, release more free VPs than initially expected. The glycosidase enzyme activities of the most promising yeasts were then characterised and showed properties compatible with winemaking conditions. Finally, combinations of the most promising yeasts and bacteria were evaluated as a possible biological solution to smoke taint. This study shows that the microbial diversity occurring in the broader grape and wine environment constitutes a reservoir of biochemical activities of great industrial interest that can be tapped into to find targeted sustainable solutions to environmental challenges.