Eric Herve,* Darren Gullick, Azeem Hasan, Anindya Pradhan, and Gordon Burns
*ETS Laboratories, 899 Adams St. Suite A, St. Helena, CA, CA 94574 
(eherve@etslabs.com)

Smoke impact in wines is caused by volatile phenols found in wildfire smoke. These compounds are absorbed by berries, where they may also become glycosylated. Both volatile and glycosylated forms eventually cause off-flavors in wines. To assess smoke impact, a selection of volatile and glycosylated phenols is proposed, mainly based on Australian research. It includes guaiacol, 4-methylguaiacol, cresols, phenol, syringol, and 4-methylsyringol, and their glycosylated forms guaiacol rutinoside, 4-methylguaiacol rutinoside, cresol rutinoside, phenol rutinoside, syringol gentiobioside, and 4-methylsyringol gentiobioside. The accurate and reproducible measurement of these compounds is now possible, due to the commercial availability of standards and isotopic analogues. Over two years, we investigated the stability of these markers in bottled wines. Wines monitored were a Chenin blanc and a Chardonnay (whites), a Grenache (rosé), two Cabernet Sauvignons, a Zinfandel, and a Grenache (reds). No significant increases in guaiacol were observed in the white or rosé wines. Slight increases (2 to 3 μg/L) were observed in red wines, with a larger increase in Pinot noir (9 μg/L). Non-significant to slight increases were observed for phenol, with a larger increase in the Zinfandel (10 μg/L). Large increases in syringol were found in red wines only, especially Cabernet Sauvignon (up to 60 μg/L). No significant increases were observed in the other volatile phenols. All glycosylated markers were stable. Therefore, increases in volatile phenols, when they happened, were not explained by hydrolysis of glycosylated forms measured. The observed increases in guaiacol and syringol and the stability of the glycosylated forms measured, are consistent with a previous study. The stability of glycosylated markers makes them relevant in identifying wines from smoke-exposed grapes, possibly for many years after bottling. A limitation is that some smoke-impacted wines may show normal or non-detectable levels.

Funding Support: ETS Laboratories, 899 Adams St. Suite A, St. Helena, CA 94574