Baseline Levels of Smoke-related Volatiles and their Glycosidic Precursors in California Grapes and Wines

Summary

The increasing incidence of wildfires in grape growing regions of California and the West Coast has highlighted the need for enhanced understanding of the levels of volatile phenols and their non-volatile glycoside precursors that contribute to smoke taint off-flavors in grapes and wines. Within the scope of this project, we conducted measurements of ten volatile phenols in non- smoke exposed grapes aiming to elucidate the baseline levels of these compounds in both red and white grape varieties. Specifically, free and total levels of guaiacol, 4-methylguaiacol (creosol), phenol, 4-ethylguaiacol, o-, m-, p-cresol, 4-ethylphenol, 4-methylsyringol, and syringol were assessed in grapes sourced from various regions across California. Concurrently, air quality data for these regions is presented. The obtained data reveal variability in concentrations across grape varieties, regions, and years. This variability underscores the necessity for extensive databases to comprehensively evaluate the impacts of smoke exposure on the composition of both free and total volatile phenols. We have submitted a proposal to continue this work in 2024-25.