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Rapid Test Identifies Wildfire Taint in Wine Grapes

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Widespread wildfires in wine producing regions have hit the headlines many times this year. For growers and producers, the potential impact of smoke exposure on grape crops can prove challenging as existing analysis methods are time consuming and subjective. Utilizing gas chromatography–tandem mass spectrometry, researchers from the University of British Columbia have devised a new test to precisely and accurately measure the amount of volatile phenols that are present in the fruit prior to wine production. These compounds are absorbed by grapes when exposed to smoke and can impact wine flavor. This work was recently featured in our news items.

We spoke to Dr Wesley Zandberg (WZ), the paper's last author, from the Department of Chemistry at the University of British Columbia Okanagan, to learn more about the new approach and how science is working with the wine industry.

KS What prompted the initiation of this body of work? Was there any drive from the wine industry?

WZ The impact of forest fire smoke on wine quality represents a significant financial challenge to the global wine industry, especially since the frequency of forest fires are predicted to increase in many growing regions (e.g., California, Australia, British Columbia).  From an analytical chemistry perspective, the issue of smoke-taint presents a variety of challenges that we felt uniquely suited to address given the expertise in our lab and that of our industrial partner, Supra Research and Development (Supra).  Moreover, if we view the phenomenon of smoke-taint as a model system for wine flavor compounds, the methods we develop and the insights we glean can be applied to the expression of positive flavor attributes in wines.

There is tremendous interest from the wine industry regarding the impact smoke-exposed grapes can have on wine quality.  More specifically, our wine industry collaborators want to know, with high probability, if they use smoke-exposed grapes will they produce smoke-tainted wine.  As such, expertise and scientific interest notwithstanding, the driving force behind this project is the development of reliable analytical tests that people in the wine industry need to more effectively manage the potential impact of smoke-exposure on wine quality.

KS Could you highlight for us how your new analysis method compares to existing techniques offered?

WZ In reviewing the existing methods used to assess for the compounds associated with the flavors and aromas of smoke-taint, it was apparent that there were gaps in our understanding of the fundamental analytical chemistry.  We addressed these gaps, with the end result being a method that provides an accurate concentration for the total sensory potential in smoke-exposed grapes.  It is our belief that having this accurate method will facilitate the correlation of the chemical composition of smoke-exposed grapes to the presence of perceptible smoke-taint – a goal that has eluded published methods thus far.

KS Wildfires have been a serious problem across North America this year and attracted considerable press coverage in relation to crop destruction and possible wine shortages. How has the test been received by growers and producers? Are there many facilities offering your test and if so what has the uptake been like?

WZ Wildfires were definitely an issue in North America in 2017.  There were also prominent fires in Chilean, Australian and South African grape growing and wine producing regions, which underscores the importance of this research to the global wine industry.  All of the growers and producers we have spoken with, including several in California and Washington, are keenly interested in advancing our understanding of how smoke exposure might impact the integrity of their supply chain.  Supra Research and Development (Kelowna, British Columbia, Canada) has implemented our methods for smoke-taint testing of grapes and wine.

KS You mention the application of this techniques not just for testing wildfire damage but also analyzing the smoky qualities in wines after production. Could you see this test being applied more widely during the blending process and a move away from the subjectivity of the human palette?

WZ As scientists, objectivity in our analyses is paramount.  The method we developed can objectively provide concentrations for compounds that we know contribute to the intensity of smoke-taint.  However, when it comes to taste, aroma and consumer preference, the application of sensory analysis by experienced wine makers and tasting panels presents a significant value to wine producers.  For instance, some consumers may prefer a strong, smoky finish to their wine, just as some people prefer very hoppy beers.  In this scenario, our test might indicate that the wine was ‘tainted’ as a result of smoke exposure during grape maturation, but consumer preference turns the supposed sensory defect into an asset.  As such, it is likely that there will continue to be a close relationship between analytical chemistry, sensory analysis and consumer preference as it pertains to quantifying the taste and flavor of wine.  This includes the presence of defects like smoke-taint and Brett-taint. That said, we have worked with wineries who have had customers tell them that their wines were smoke-tainted, even though these were made from grapes harvested decades after potential smoke exposure (all the available evidence collected to date indicates this is impossible).  In such cases our test could be used to objectively demonstrate the absence of compounds linked to the smoky aroma of wines.

KS How do you see the research field moving forward in the future? Could the technique be applied to wine characteristics other than smokiness, tannins for example?

WZ Due in large part to their inherent heterogeneity, tannins possess a set of analytical challenges that are beyond the scope of the methods we developed for assessing smoke-taint.  However, there are several active research areas regarding smoke-taint that will contribute to the ability of grape growers and wine producers to effectively manage their products in the event of smoke-exposure.  Foremost to wine producers, is ongoing research in our lab aimed at: 1) developing a predictive model for the presence of perceptible smoke-taint based on the chemical composition of smoke-exposed berries; 2) in-winery solutions to mitigate the impact of smoke-exposure; and 3) on-vine treatments to reduce the uptake of volatile phenolic compounds in grapes during smoke exposure. In the longer term, we believe that the techniques developed for studying the phenomena of smoke taint will be readily adapted to other important classes of grape compounds responsible, for example, for wine flavor/aroma (terpinoids) and color/antioxidant potential (phenylpropanoids): in both of these cases the responsible grape compounds are affected by the yeast during fermentation in ways that are likely similar to the compounds associated with smoky aroma.

Dr Wesley Zandberg was speaking to Dr Karen Steward, Science Writer for Technology Networks.