Evaluation of passive samplers as a cost-effective method to predict the impact of wildfire smoke in vineyards prior to harvest

Authors: Rumbaugh, Arran; KHLYSTOV, ANDREY - Desert Research Institute; CAMPBELL, DAVE - Desert Research Institute; SON, YEONGKWON - Desert Research Institute; WEN, YAN - Desert Research Institute; LIANG, CHEN - University Of California, Davis; FANG, HAO-LIN - University Of California, Davis; WALLIS, CHRISTOPHER - University Of California, Davis; WEXLER, ANTHONY - University Of California, Davis

Submitted to: Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2024
Publication Date: 1/15/2025
Citation: Rumbaugh, A.C., Khlystov, A., Campbell, D., Son, Y., Wen, Y., Liang, C., Fang, H., Wallis, C., Wexler, A. 2025. Evaluation of passive samplers as a cost-effective method to predict the impact of wildfire smoke in vineyards prior to harvest. Food Chemistry. Volume 463, Part 2, 15 January 2025, 141191. https://doi.org/10.1016/j.foodchem.2024.141191.
DOI: https://doi.org/10.1016/j.foodchem.2024.141191

Interpretive Summary: Grapes are the highest value fruit crop grown in the United Sates with the American wine industry generating over $276 billion for the US economy. California alone contributes over $88 billion, largely due to tourism. One of the newest threats to the wine industry is smoke produced from wildfires. In 2020, the United States experienced severe wildfires from May through December, burning over 10 million acres. It is estimated that the US grape and wine industry suffered economic losses around $3.7 billion due to wildfires and smoke exposure in vineyards. As this threat is likely to increase globally due to climate change predictions, efforts are needed to quickly determine the level of impact in a vineyard during and after a smoke event. After wildfires in Australia, wines produced from smoke exposed grapes exhibited “smokey”, “dirty”, “burnt”, “earthy”, and “smoked meat” characteristics. Researchers have now associated this sensorial impact to elevated levels of volatile phenols (VPs) in grapes and wines. Current methodologies to analyze free and bound (glycosylated) VPs in grapes and wines require GC-MS/MS and LC-MS/MS techniques, respectively. These methods are time extensive, expensive, and require trained personnel to prepare and analyze samples. Interestingly, little information is available to correlate atmospheric levels of VPs to the concentrations in grapes or wines, even though the ratio’s between guaiacol and syringol can be used to determine the lignin source (hardwood vs. softwood). The availability of VP measurements in smoke that could relate to concentrations in grapes and wines would allow better estimation of potential impact of smoke on the viticulture industry. An "early warning system" of this type has been implemented in Australia since 2016, with reported success in reducing financial losses to growers. Their system, which has received substantial government support, uses active samplers that require on-site power and equipment which can be costly. Herein, we exemplify the potential of passive samplers as an inexpensive, alternative method to monitor VP levels in smoke and determine the level of severity after a smoke event. Since wildfires are unpredictable in nature, we analyzed the efficacy of the passive samplers during intentional, controlled smoking experiments across various exposure durations and smoke densities. Our initial data indicates a strong correlation between the levels of VPs in the passive samplers to total VPs in the grapes and wines, suggesting the viability of this tool to be used as an early warning sign of smoke impact in vineyards.

Technical Abstract: Climate change events have increased wildfire frequency and length of the fire season globally, which directly and indirectly affect agricultural systems. For vineyards globally, smoke exposure can alter fruit chemistry, resulting in negative sensory characteristics in wines. Collectively this phenomenon was termed “smoke taint” and was found to be associated with elevated levels of smoke-derived volatile phenols (VPs) in grapes and wines. The current work sought to create a predictive tool that could correlate levels of VPs in smoke with concentrations in grapes and wines. Therefore, Cabernet Sauvignon grapes and diffusive passive samplers were intentional exposed to smoke at four different exposure levels: control (no exposure), low exposure, medium exposure, and high exposure. Following, wines were made from smoke exposed fruit in one-liter fermenters. Passive samplers were analyzed for free VPs whereas grapes and wines were analyzed for free and glycosylated (bound) VPs. As expected, concentrations of VPs in grapes were positively associated with the level of smoke exposure. Interestingly, levels of VPs in the passive samplers had a strong positive correlation with VP concentrations in grapes (R2=0.9999). Although the current sample number is too small to accurately build a predictive model/tool, this is promising information to correlate VPs in smoke with concentrations in grapes and wine and predict impact in final wines.