Quantifying the impact of forest fire smoke on grapes and wine

In 2017, vineyards in the Okanagan Valley of British Columbia, Canada experienced prolonged smoke exposure, raising concerns from the local wine industry about the potential impact to the 2017 vintage. Similarly, wildland fires in the wine-producing regions of California, Washington, Chile, South Africa, and Australia in 2017, and the predicted increase in the frequency of forest fires in the abovementioned wine-producing regions, have brought the impact of smoke exposure on the quality of grapes and the resulting wines to the forefront. In collaboration with Dr. Wesley Zandberg at the University of British Columbia Okanagan, Supra Research and Development initiated a research program aimed at understanding how smoke exposure impacts the quality of grapes and wine, with an emphasis on products grown and produced in the Okanagan Valley.

We know that wine made from grapes exposed to forest fire smoke

may possess negative aromas and flavours (e.g., ‘ashy’, ‘barnyard’, ‘band-aid’) and/or a dearth of varietal characteristics that are collectively termed smoke taint. A family of volatile compounds (VCs), which we can taste and smell, and their sugar-bound derivatives, correlate to the intensity of smoke taint in wine. Although the sugarbound compounds are tasteless and odourless, fermentation can transform these compounds, making them perceptible in the wine as smoke-taint. There is also evidence suggesting that the sugar-bound VCs can be changed by oral bacteria and during bottle aging, such that the VCs can be perceived in the wine. But the sugar-bound VCs are not the whole story. By studying grapes from vineyards in the Okanagan Valley, we have preliminary evidence for additional (non-sugar) bound forms of VCs in smoke-exposed grapes that likely contribute to the presentation of smoke taint in wine. As well, we demonstrated that the chemistry of smoke-exposed grapes and the resulting wine may have a geographic signature, meaning smoke taint in Australia is likely different from smoke taint in North America.

From speaking with industry stakeholders, the most pressing issue regarding smoke taint is how grape growers and wine producers can reliably manage product quality in the event of smoke exposure. Currently, the gold standard is to perform small-scale fermentations with subsequent tasting. Alternatively, you can quantify the VCs and their sugarbound forms in grapes. The former approach is resource-intensive and requires up to two weeks to obtain results, while the latter is only 50-to80 per cent predictive of perceptible smoke-taint in wine. We are working with local vineyards to provide the wine industry with the reliability they need by refining existing approaches

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and developing new techniques to accurately quantify the relevant VCs in smoke-exposed grapes and correlate those values to the presence of perceptible smoke taint in wine.

To ultimately make our new testing approaches predictive, a large-scale survey of different varietals over several growing seasons is required. This will establish baseline levels of smoke taint-associated VCs in different cultivars, many of which are found naturally in grapes, albeit at lower concentrations than after smoke exposure. Knowing the baseline levels will, in turn, allow us to determine how much of a relative change in smoke taint-associated VCs can yield perceptible smoke taint in wine. A similar program exists through the Australian Wine Research Institute, which gives their industrial stakeholders a significant competitive advantage when it comes to monitoring the quality of their grapes and wine following smoke exposure.

The knowledge base we develop as

part of our smoke taint research

can also be applied to compounds

with positive sensory associations

(e.g., terpenoids, flavonoids, vanillin,

etc.), which share much of the grape and wine-related biochemistry EnartisUSA_Zenith tr.indd 1

associated with smoke taint. As well, our understanding of smoke taint could be used to rationally develop protective strategies that would reduce the impact of smoke exposure either in-vineyard, or as part of the fermentation process. Productive collaborations between academia, the wine industry, and commercial laboratories will ensure this knowledge base continues to expand.

For further information regarding testing for smoke taint or any other analytical testing you require for grapes or wine, please contact Supra Research and Development. o

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