Matthew Noestheden,* Eric Dennis, Seamus Riordan-Short, Benjamin Noyovitz, Brandon Whitemore, and Wesley Zandberg
*University of British Columbia Okanagan, Supra Research and Development, 1177 Research Rd, Kelowna/BC/V1V1V7, Canada (noesmatt@gmail.com)

It is well established that the concentration of volatile phenols and their glycosides correlate with a wine defect known as smoke taint, which can occur when fermentation is performed using Vitis vinifera berries that were exposed to forest fire smoke. There are conflicting reports regarding the stability of the volatile phenolic glycosides that survive fermentation, with some studies suggesting their hydrolysis can increase the intensity of smoke taint during bottle aging. Conclusive data, based on chemical stability tests and controlled small-batch fermentations, demonstrated a lack of glycoside hydrolysis in wine that will be discussed, as well as what these data tell us about other compounds that may correlate to smoke taint. V. vinifera naturally produces volatile phenols like guaiacol and syringol via the phenylpropanoid and/or shikimic acid metabolic pathways. An influx of exogenous volatile phenols from smoke could change the relative concentrations of secondary metabolites associated with these biosynthetic pathways. Additionally, since phenylpropanoids are, in part, regulated by plant stress, it is conceivable that smoke exposure could induce changes in the endogenous expression of phenylpropanoids, independent of the presence of smoke-borne volatile phenols. To investigate these hypotheses, the concentrations of key metabolites in the phenylpropanoid/shikimic acid pathways were analyzed in smoke-exposed and control berry and wine samples. The impact of these studies on the objective assessment of smoke taint in grapes will be discussed. Finally, the enzymatic activity of four Saccharomyces strains was explored by performing fermentations on smoke-exposed berries and monitoring the volatile phenols produced following primary fermentation. The results of these fermentations will be presented as a starting point to develop in-winery solutions to mitigate the ongoing impact of forest fires.  

Funding Support: MITACS Accelerate Natural Sciences and Engineering Research Council, British Columbia Wine Grape Council