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 into berries, where they may also become glycosylated. Both volatile and glycosylated forms eventually cause off-flavors in wines. In large wildfire events, economic losses for all wine industry actors can be devastating. 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, in addition to 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. The 2020 vintage was particularly affected by wildfires all over the Western United States, giving us an opportunity to collect extensive data for this suite of markers in wines made from smoke-exposed grapes. In the large majority of cases, levels of both volatile and glycosylated markers in wines appeared closely related to the intensity of vineyard smoke exposure. This confirms the relevance of these markers in the Western United States. In some cases, however, volatile markers were relatively low, sometimes barely indicating any exposure to smoke, while glycosylated markers were high. This suggests very efficient glycosylation mechanisms in some grapes and vines exposed to smoke. We also observed the opposite pattern: high levels of volatile markers in combination with low levels of glycosylated markers. This may be the consequence of impaired glycosylation pathways in the plants, possibly related to a severe heat wave experienced in mid-August 2020. These observations confirm that measuring both volatile and glycosylated markers is advisable to identify wines from smoke-exposed grapes. 

Funding Support: ETS Laboratories