Lik Xian Lim, Cristina Medina-Plaza, Ignacio Arías-Perez, Yan Wen, Bishnu Neupane, Larry Lerno, Jean-Xavier Guinard, and Anita Oberholster*
*UC Davis, 595 Hillgard Lane, Department of Viticulture and Enology, Davis, CA, 95616 (aoberholster@ucdavis.edu)

Fresh smoke from wildfires releases volatile phenols (VPs) due to the thermal degradation of wood lignin. VPs are absorbed into grape berries and rapidly glycosylated. Wines made from smoke-affected grapes are characterized as having smoky, medicinal aromas and a retro-nasal ashy aftertaste. Around 15 to 20% of general consumers are anosmic towards the ashy character of smoke. This study investigated the baseline levels of VPs in grapes across seven different red wine varietals spread across California and the sensory differences between the smoke-affected and non-smoke-affected wines using modified descriptive analysis (DA), gas chromatography-mass spectrometry, and liquid chromatography-triple quadrupole tandem mass spectrometry of the free and total VPs, and individual bound glycosides, respectively. The amount of smoke exposure was the largest contributor to smoke impact, but different wine matrices from different locations and varietals were also important in determining the level of perceived smoke impact. Low smoke-affected wines determined by free and total VP concentrations were not significantly different from the non-affected wines when rated by DA. The study also investigated the difference between the sensitivity of experts and non-experts towards smoke. From the same location, smoke-affected and non-smoke-affected wines made from Cabernet Sauvignon, Malbec, and Syrah grapes, respectively, were blended through serial dilutions to achieve wines with different levels of smoke impact. Wines were evaluated using a series of hedonic questions, just-about-right, and check-all-that-apply. The results indicate that experts could determine smoke impact at lower percentages of smoke-affected wine included in the wine blend than non-experts, who only distinguished smoke impact at higher percentages of smoke-affected wine in the wine blend, and thus smoke marker compounds. Research findings from both studies contribute to our understanding of grape smoke exposure and how it affects wine quality as determined by instrumental measurements, wine experts, and non-experts.

Funding Support: Jackson Family Wines, USDA-ARS