Enology - Smoke Exposure in Grapes and Wine Session

Francesco Maioli | Breanna Garman | Ron Runnebaum | Arran Rumbaugh*

Influence of Berry Skin Cuticular Wax on Smoke-Derived Volatile Phenol Uptake in Grapes

Francesco Maioli, Breanna Garman, Ron Runnebaum, and Arran Rumbaugh*

*USDA-ARS, 595 Hiilgard Lane, Davis, CA, 95616, arran.rumbaugh@usda.gov

Wildfire smoke exposure can alter grape composition and cause “smoke taint” in the resulting wines, causing significant economic losses (USD 3.7B in the United States in 2020). Moreover, rising fire intensity and duration due to climate change are increasing the relevance of smoke exposure across viticultural regions worldwide, including Portugal, Spain, and Chile. While the chemical nature and sensory implications of smoke-derived volatile phenols (VPs) have been widely reported in the literature, comparatively less attention has been given to the role of grape berry skin properties in modulating smoke compound uptake. This study examined the role of cuticular wax quantity and composition in influencing the uptake of smoke-derived compounds by grapes. Seven grape genotypes characterized by differing berry skin wax were selected for controlled smoke exposure experiments. Grape clusters and individual berries were separated into four treatments in a factorial design defined by cuticular wax status (intact or removed using chloroform) and smoke exposure (present or absent). Berries and clusters were exposed to artificial smoke under controlled conditions at two phenological stages of maturity. VPs in grapes were quantified by gas chromatography-tandem mass spectrometry (GC-MS/MS). Cuticular wax was determined gravimetrically and chemically characterized, after derivatization, by GC-MS/MS. Grape berry skin and tissue morphology and thickness were also evaluated using scanning electron microscopy and light microscopy. Smoke exposure increased VP concentrations across all genotypes and sample types (WAX or NO WAX). In particular, smoke-exposed berries differentiated according to wax presence, abundance and composition, clearly highlighting the protective role of cuticular wax against VP uptake. These findings identify cuticular wax influencing grape response to smoke exposure and provide new insights into genetic variability in smoke taint susceptibility, with implications for vineyard risk assessment and mitigation strategies under increasing wildfire pressure.

Funding Support: USDA-ARS

Julie Hilland | Robert Coleman | Thomas Collins*

Wine Volatile Phenol Glycoside Compositional Change During Rapid Aging and Characterization of Acid Hydrolysis Reactions

Julie Hilland, Robert Coleman, and Thomas Collins*

*Washington State University, 359 University Drive, Richland, WA, 99354, tom.collins@wsu.edu

During aging, wine produced from smoke-exposed grapes can develop undesirable sensory characteristics. Given the negative on wine quality, reliable methods to measure “free” volatile phenols (VP) and “bound” (VP-glycosides) in wine are critical to evaluate smoke impact severity. Although the stability of VP-glycosides in smoke-affected wine has been studied in long-term aging trials, potential hydrolysis reactions (in smoke-affected wines, spiked non-affected wines, and spiked model wines) during rapid aging in commercial incubators have not been evaluated. Gas chromatography mass spectroscopy (GC-MS) is used to measure “free” VP while “bound” VP, released from VP-glycosides during wine aging, are indirectly measured through the coupling of laboratory acid hydrolysis followed by GC-MS quantification. Currently, there is no standard protocol for acid hydrolysis. The lack of standardization leads to analytical variability among laboratories as it affects the degree to which VP-glycosides are hydrolyzed. This study has two objectives: evaluate compositional changes of VP and VP-glycosides in smoke-affected wine, spiked non-affected wines, and spiked model wine during rapid aging; and characterize hydrolysis reactions of individual VP-glycosides at specific time points using a controlled acid hydrolysis method. Rapid aging was conducted by incubation at 35°C. Samples were collected at 3-wk intervals. Using closely controlled acid hydrolysis conditions, VP and VP-glycosides were analyzed in a time course study, with sampling at regular intervals for quantification throughout hydrolysis. In each objective, the use of both GC-MS and high-pressure liquid chromatography coupled quadrupole time of flight (QTOF) MS allowed for mass balance and percent recovery calculations for the novel hydrolysis methodology as well as insight into VP-glycoside hydrolysis behavior throughout the hydrolysis procedure.

Funding Support: USDA/SCRI, USDA-ARS

Jillian Thrall | Camilla Sartori | Elizabeth Tomasino*

Chemical Composition Versus Sensory Reality: Investigating Smoke Phenol Interactions in Red Wine Matrices

Jillian Thrall, Camilla Sartori, and Elizabeth Tomasino*

*Oregon State University, 3051 SW Campus Way, Corvallis, OR, 97331, Elizabeth.Tomasino@oregonstate.edu

As wildfires around the world threaten vineyards and wineries, it is becoming increasingly important for winemakers to understand the sensory impacts of smoke compounds. The sensory impact of volatile compounds is governed not only by their individual concentrations, but by complex interactions within the aroma matrix. Traditional approaches to aroma prediction have relied heavily on odor activity values (OAVs), which compare compound concentrations to detection thresholds. Mounting evidence suggests OAVs alone are insufficient to predict aroma perception in complex mixtures, as discrepancies are often found between analytical and sensory outcomes. Many aroma compounds are involved in creating the off-flavor in smoke-exposed wines, primarily seven phenolic compounds: guaiacol, 4-methylguaiacol, o-cresol, m-cresol, p-cresol, syringol, and 4-methylsyringol. This study uses these phenols as a model to observe how changes in compound mixtures can alter aroma perception. Three experimental scenarios were designed to investigate interaction effects: (1) constant total phenol concentration with varying compound ratios, (2) inclusion versus omission of syringols to assess their sensory relevance beyond marker status, and (3) mixtures with identical compound ratios presented above and below individual odor thresholds. Three specific ratio groupings were evaluated in Pinot noir and Cabernet Sauvignon wines by check-all-that-apply and descriptive analysis using intensity scales to determine the intensity of aroma descriptors in the wines. It was revealed that aroma perception was primarily driven by overall concentration. Syringols showed no significant sensory impact, supporting their role as exposure markers rather than aroma-active contributors. Differences between Cabernet Sauvignon and Pinot noir perception confirm that base matrix affects resistance to changes in aroma. These findings emphasize the importance of matrix interactions in predicting aroma outcomes from chemical data. A deeper understanding of volatile phenol interactions enhances the interpretability of analytical results and supports more informed decision-making for winemakers faced with smoke events in the vineyard.

Funding Support: USDA National Institute of Food and Agriculture and USDA-Agricultural Research Service (ARS) project number 2072-21000-057-00D. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and should not be construed to represent any official USDA or U.S.

Gauthier Lagarde | Liang Chen*

Insight into the Occurrence and Evolution of Thiophenols in Wine

Gauthier Lagarde and Liang Chen*

*Department of Viticulture and Enology, UC Davis, 595 Hilgard Ln, Davis, CA, 95616, liichen@ucdavis.edu

Volatile thiols are key contributors to wine aroma due to their strong odor properties and low sensory thresholds. While tropical‑smelling varietal thiols have been widely studied, thiophenols were identified only recently and remain poorly characterized. Baseline data on these ultra‑trace thiols is limited, and the influence of grape variety, winemaking practices, and wildfire smoke exposure on thiophenols is still unclear. In this study, an ultra-high-performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) method was developed and validated to quantify 11 thiophenols, including seven previously unreported thiophenols in three wine matrices. This method was applied to screen a wide selection of Californian wines, establishing an initial baseline of their occurrence. In wines produced from smoke‑affected grapes, volatile phenols were also measured and compared with thiophenol levels. Additional trials examined thiophenol stability and evolution in both control wines and smoke‑exposed wines. Concentrations of volatile phenols and added thiophenols were tracked over time under varying conditions. By combining method adaptation, baseline screening, and targeted stability trials, this work provides new insight into the distribution and evolution of thiophenols in wine.

Funding Support: Department of Viticulture and Enology, UC Davis

3:15 pm – 3:35 pm	Influence of Berry Skin Cuticular Wax on Smoke-Derived Volatile Phenol Uptake in Grapes Francesco Maioli, University of California, Davis
3:35 pm – 3:55 pm	Wine Volatile Phenol Glycoside Compositional Change During Rapid Aging and Characterization of Acid Hydrolysis Reactions Julie Hilland, Washington State University, Richland
3:55 pm – 4:15 pm	Chemical Composition VS. Sensory Reality: Investigating Smoke Phenol Interactions in Red Wine Matrices Jillian Thrall, Oregon State University, Corvallis
4:15 pm – 4:35 pm	Insight into the Occurrence and Evolution of Thiophenols in Wine Gauthier Lagarde, University of California, Davis

Enology – Smoke Exposure in Grapes and Wine Session

Research Reports

Moderator:

Speakers:

Share This Page