Ruiwen Yang, Yanping L. Qian, Armando Alcazar, and Michael C. Qian*
*Oregon State University, 100 Wiegand Hall, Corvallis OR, Corvallis, OR 97330 (michael.qian@oregonstate.edu)

Guaiacol, 4-methylguaiacol, and o-, p-, and m-cresol are believed to relate to grape and grapevine exposure to smoke generated from wildfires. Both guaiacol and 4-methylguaiacol are widely used as indicators of smoke exposure. In this study, 86 Pinot noir wines were randomly selected from 2013 to 2016 vintages, with ~20 samples from each year as control wines. The samples were obtained from industry fermentation without barrel aging. Guaiacol, 4-methylguaiacol, and o-, p-, and m-cresol in the wines were analyzed using solid-phase microextraction-gas chromatography-mass spectrometry with stable isotope compounds as internal standards. Total volatile phenols were also analyzed after the sample was hydrolyzed with HCl for 4 hr at 100°C (pH 1.2). The results were compared with >300 smoke-exposed red wine samples collected during the 2020 wildfire season. T-test, correlation heatmap, individual correlations, principal component analysis, and partial least squares discriminant analysis were used to compare the smoke-exposed and control wines. The results showed that smoke-exposed red wine presented the data’s biggest dispersion, and o-, p-, and m-cresol exhibited the biggest difference across samples. A similar trend was observed for total phenols, with total p-cresol exhibiting the greatest difference. Except for free 4-methylguaiacol and total m-cresol, all other volatile phenols were significantly more abundant in smoke-exposed wine (p > 0.05). Univariate data analysis suggested that total p-cresol is the most discriminating compound for smoke exposure, followed by free o-, p-, and m-cresolcresol.

Funding Support: American Vineyard Foundation (AVF), Oregon Wine Board (OWB) and Oregon Wine Research Institute (OWRI)