Megan Meharg, Mackenzie Aragon, Caroline Merrell, and Tom Collins*
*Washington State University, 359 University Dr, Richland, WA, 99354 (tom.collins@wsu.edu)

Wildfire and controlled burn events pose an economic threat to the global wine industry. Smoke-derived volatile phenols (VPs) exist as free and bound glycosidic precursors that are released during fermentation-driven enzymatic hydrolysis, but the role that yeast might play in thiophenol production has not been studied. Free VPs and thiophenols of smoke-affected wines have been shown to cause perception of undesirable attributes such as meaty, smoky, medicinal, and ashy aromas and flavors. Here we studied the effect of commercially available yeast strains on the concentrations of known smoke-derived VP and thiophenol markers. Grapevines (Vitis vinifera cv. Merlot) were experimentally exposed to smoke in a semi-controlled environment. Smoke-exposed and non-exposed grapes were fermented using 12 commercial yeast strains over two vintages. Gas chromatography-mass spectrometry confirmed the increased concentrations of VPs in wines from smoke-affected fruit compared to the control wines, but there were no differences in concentrations of VPs among the tested yeast strains. Investigation of thiophenols using high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry revealed differences between control and smoke wines in the relative peak area for thioanisole and thiophenol, but not for thiocresols or thioguaiacol. There were, however, differences among yeast strains for total thiocresols (m-, o-, and p-isomers) and for thioguaiacol. Our study suggests that commercial yeast strains play a role in the release of VPs and the concentration of thiophenols.

Funding Support: USDA, Washington Wine Commission, Jackson Family Wines.