UPDATED: Viticultural area is Kelsey Bench, not Kelseyville Bench.
UC Cooperative Extension study shows smoke damage to grapes not uniform across vineyards
By the time the Mendocino Complex Fires were officially contained on Oct. 4, 2018, five weeks after igniting, they had burned approximately 450,000 acres in Colusa, Lake, Glenn and Mendocino counties, making it the largest wildfire in California history, according to CalFire.
The fire not only destroyed 280 homes and other buildings, its smoke destroyed the market for wine grapes grown in vineyards near burned areas.
Fearing grapes near the fire would impart smoke flavors to the wine, some wineries rejected all fruit from nearby regions of Lake County and Potter Valley, leaving grape growers to hastily find new destinations for their 2018 crop.
“It can be difficult to determine if fruit has been compromised in quality when exposed to wildfire smoke, and whether or not smoke flavors will result in wine when fermented,” said Glenn McGourty, UC Cooperative Extension advisor in Mendocino County.
A new UC Cooperative Extension study shows wind direction and speed, temperature and a vineyard's proximity to an active fire are factors that can help growers and winemakers predict smoke damage to fruit.
“Fruit in my own vineyard, 60 feet across the street from where the fire started, had no smoke damage because the wind was blowing away from it,” McGourty said.
Due to the Mendocino Complex Fires, an estimated $41 million worth of winegrapes, which would have been sold at full price, were impacted – some were sold at a discount, some were sold to other customers, some were custom crushed, while some were left hanging in the vineyard, according to the Lake County Winegrape Commission and Mendocino County Farm Bureau.
The wine industry needed a scientific method of determining whether grapes could be made into a wine untainted by smoke. With funding from the Lake County Winegrape Commission, McGourty formed a workgroup of local growers and winemakers with Anita Olberholster, UC Cooperative Extension enology specialist in the Department of Viticulture & Enology at UC Davis, to research when fruit quality has been compromised.
“The need for industry standards regarding the impact of wildland smoke on winegrapes and the resulting wines has become even more pressing over the past few years,” said Debra Sommerfield, president of the Lake County Winegrape Commission.
Science showed the intensity, duration and timing of the exposure to wildfire smoke affects the grape's uptake. Generally, the closer to harvest, the greater risk to the fruit.
“Both the fruit and wine samples in our study showed a wide range of volatile phenol and glycocide concentrations, indicating that smoke damage to fruit was not uniform across the vineyards sampled,” McGourty said.
Volatile phenols and glycosides create off-flavors
Fresh smoke contains volatile phenols and glycosides that can affect fruit, but these chemicals tend to dissipate in the atmosphere in 1 to 2 hours. Vineyards close to actively burning fires and in the path of fresh smoke are most likely to be affected by smoke taint. Smoke that travels long distances is less likely to affect grapes and the wine made from the fruit.
The combination of volatile phenols and glycosides create “smoke taint” – both aromatic and tactile in the mouth. Wine drinkers may smell smoke or other off flavors and experience a drying of their mouth when high concentrations of the chemicals are present in wine.
“At lower concentrations, smoke taint reminds you of brett-affected wines,” Oberholster explained, referring to the yeast brettanomyces. “There is a shortness of fruit, a kind of dryness in the mouth that you know isn't normal. There may be barely perceptible aromas that aren't normal as well.”
Following wildfire smoke exposure, the researchers sampled fruit from 14 cabernet sauvignon vineyards around the viticultural areas of Lake County, including Upper Lake, High Valley, Big Valley, Kelsey Bench, Red Hills, Lower Lake and Guenoc Valley. As a control, fruit was also sampled from a Napa Valley vineyard that was not exposed to wildfire smoke.
“The volatile phenols guaiacol and 4-methyl guaiacol are detected in the fruit by gas chromatography, so it is possible to sample fruit before harvest to make picking decisions,” McGourty said. “Based on our study, berry sampling and guaiacol/ 4-methyl guaiacol analysis are useful for a quick evaluation of whether or not fruit from a particular vineyard may have the presence of volatile phenols that can potentially result in smoke-affected wine.”
Testing the fruit for volatile phenols and glycosides is both expensive and not completely predictive as standards are not well defined for damage based on smoke chemical concentration, he cautioned.
These two compounds aren't the only ones that cause smoke flavors. More than 70 other compounds in forest fire smoke can also produce undesirable flavors and odors described as “like licking an ash tray, burnt garbage, a burnt potato, a campfire that has been drenched with water.”
The taste test
To assess the levels of the compounds that produce the off-flavors, Oberholster convened a panel of 14 wine industry professionals to taste the sample wines. The wine tasters detected stronger off-flavors in the wines made from riper fruit, which also contained higher concentration of smoke compounds. Less than 6 micrograms per liter of the smoke compounds were difficult for the tasters to detect, leading the researchers to conclude they will have a minimal effect on wine quality.
Smoke from a distant fire
The scientists also looked at the influence of distance from the fire and elevation on smoke taint. They found some vineyards close to the edge of fires and immediately downwind were heavily affected, with the grapes containing high concentrations of the smoke flavor-causing compounds. But they determined elevation was not a factor in smoke flavors in wines.
Wind direction and speed, temperature and vineyard proximity to active fires are highly likely affect whether there will be smoke damage to the fruit, their research showed.
“Smoke generated in the first one or two hours from a wildfire is most damaging to nearby vineyards,” McGourty said. “Even though a vineyard may be enveloped in smoke, if the source of the smoke is from a distant fire, it will probably won't seriously damage the fruit quality because most of the volatile gases are gone.”
Lake County Winegrape Commission's Sommerfield said, “Today, the results of this study are already proving to be useful in deepening our understanding of smoke and the risks it poses to grapes and wine, in enabling grape growers and winery buyers to engage in fruitful discussions and make informed decisions, and, in turn, in helping to propel the development of industry standards and protocols.”
To read more about the study by McGourty, Michael I. Jones, Oberholster and Ryan Keiffer, see the January 2020 edition of Wine Business Monthly at https://www.winebusiness.com/wbm.
“This is a great little study, the first one that I know of that takes a systems approach to evaluating the effects of wildfire smoke,” said McGourty.
Glenn McGourty, UCCE viticulture advisor for Mendocino County, describes for Hannah Bird the UC project to analyze the effect of wildfire smoke on winegrapes.
Researchers who have been investigating the impacts of the Camp Fire and other urban fires in Northern California will gather June 4 in Chico to share what they have learned. Members of the public are invited to attend the Camp Fire Water Resources Monitoring and Research Symposium, which will be held at the California State University, Chico Farm located at 311 Nicholas C Shouten Lane, Chico, CA 95928.
“The recent urban fires across California have raised questions about the fire impacts on watershed health, food safety and groundwater,” said Tracy Schohr, UC Cooperative Extension livestock and natural resources advisor for Butte, Plumas and Sierra counties, who is organizing the symposium.
“The Camp Fire Water Resources Monitoring and Research Symposium on June 4 creates a forum for researchers across a broad spectrum of disciplines to share findings from research conducted in Butte County and across the North State.”
“Chico State is partnering with University of California Cooperative Extension to host this educational symposium to help our community understand the impacts of the Camp Fire,” said Kasey DeAtley, Chico State professor in the College of Agriculture. “In a region rich in natural resources and agriculture production, there has been significant interest in the topic of urban fire implications and researchers have been working hard to find answers that will be shared at the symposium.”
The program will start at 9 a.m. and will feature three sessions. The day will kick off with a session titled “First Year Findings,” looking at initial rapid response for water quality, surface water monitoring, groundwater monitoring and more.
The second session is on “Urban Fires Impacts on Food and Agriculture” and will feature research presentations from UC Cooperative Extension on livestock drinking water quality and forage, eggs laid by backyard poultry, fruits and vegetables grown in gardens, and post-fire forest management.
The symposium will conclude with a session on future investigations, with Chico State professors sharing an overview of a comprehensive study underway to understand the impacts of the Camp Fire on water quality and soil health.
For more information and to register, visit https://ucanr.edu/sites/Rangelands. The event is $50 to attend and includes program materials, morning refreshments and lunch. Parking is free at the Chico State Farm.
Fire Impact and Risk Evaluation (FIRE) survey.
“We will aim to quantify the impact of wildfires in different livestock production systems,” said Beatriz Martínez López, director of the Center for Animal Disease Modeling and Surveillance in the UC Davis School of Veterinary Medicine. “The idea is also to create a risk map showing areas more likely to experience wildfires with high economic impact in California.
“This economic and risk assessment, to the best of our knowledge, has not been done and we hope to identify potential actions that ranchers can take to reduce or mitigate their losses if their property is hit by wildfire.”
Martínez López, who is also an associate professor in the Department of Medicine & Epidemiology at UC Davis, is teaming up with UC Cooperative Extension livestock and natural resources advisors and wildfire specialists around the state to conduct the study.
“Right now, we have no good estimate of the real cost of wildfire to livestock producers in California,” said Rebecca Ozeran, UC Cooperative Extension livestock and natural resources advisor for Fresno and Madera counties. “Existing UCCE forage loss worksheets cannot account for the many other ways that wildfire affects livestock farms and ranches. As such, we need producers' input to help us calculate the range of immediate and long-term costs of wildfire.”
Stephanie Larson, UC Cooperative Extension livestock and range management advisor for Sonoma and Marin counties, agreed, saying, “The more producers who participate, the more accurate and useful our results will be.”
“We hope the survey results will be used by producers across the state to prepare for wildfire,” said Matthew Shapero, UC Cooperative Extension livestock and natural resources advisor for Ventura and Santa Barbara counties, “And by federal and private agencies to better allocate funds for postfire programs available to livestock producers.”
The survey is online at http://bit.ly/FIREsurvey. It takes 15 to 30 minutes, depending on the number of properties the participant has that have been affected by wildfire.
“Survey answers are completely confidential and the results will be released only as summaries in which no individual's answers can be identified,” said Martínez López. “This survey will provide critical information to create the foundation for future fire economic assessments and management decisions.”
- Author: Jeannette E. Warnert
University of California Agriculture and Natural Resources (UC ANR) is a division of the University with scientists based on three UC campuses and in UC Cooperative Extension offices serving all California counties. UC ANR conducts research and shares research-based information with the public about wildfire, agricultural production, environmental stewardship, water policy, youth development and nutrition.
UC ANR Cooperative Extension weed specialist at UC Riverside
Management of invasive plants that introduce or alter fire regimes
UC ANR Cooperative Extension specialist at UC Berkeley
Land change science including fire and land use planning
UC ANR Cooperative Extension natural resources advisor for Los Angeles and Ventura counties
Plant arrangement, building design and maintenance to reduce fire risk, invasive weeds and pests contributing to fire risk
UC ANR Cooperative Extension natural resource monitoring specialist
Geographic information science, mapping forests
UC ANR Cooperative Extension natural resources advisor in the Central Sierra
Fire adapted communities, fire hazard mitigation in forests, post fire restoration
“Living with Fire in the Tahoe Basin” website, http://www.livingwithfire.info/tahoe/
UC ANR Cooperative Extension natural resources advisor
Desert species, invasive plants and fire
Professor of earth sciences, UC ANR Agricultural Experiment Station, UC Riverside
Fire ecology of Southern California, Baja California, and temperate Mexico; exotic plant invasions, climate change.
UC ANR Cooperative Extension wildfire specialist in the Department of Environmental Science, Policy and Management at UC Berkeley. He is located in Santa Barbara County.
Wildland fire, fire modeling, fire effects, shrubland ecosystems and spatial patterns of fire disturbance, climate change adaptation
Associate professor of Forest Ecology, UC ANR ecologist
UC Cooperative Extension Area fire advisor - Northern California
Fire ecology and management
Plant pathology professor, UC ANR pathologist
Fire and infectious disease
UC ANR Cooperative Extension natural resources advisor
Public participation in resource management
UC Cooperative Extension area forestry and natural resources advisor in Shasta, Trinity and Siskiyou counties
Forest management and wood use
Environmental science professor at UC Davis and UC ANR ecologist
Forest plot mapping
UC ANR Cooperative Extension area natural resources wildlife specialist for Southern California
Conservation of wildlife, wildlife management at the urban-wildland interface, and response of plants and animal species to fire
Professor of fire science and co-director Center for Fire Research and Outreach at UC Berkeley, UC ANR fire scientist
Fire ecology, fire behavior, wildfire, fuels treatments, forest mortality, fire policy
UC ANR Cooperative Extension forestry specialist in the Department of Environmental Science, Policy and Management at UC Berkeley and co-director Center for Fire Research and Outreach
Economics of fire prevention and fire suppression programs
UC ANR Cooperative Extension forest advisor in Humboldt and Del Norte counties and member of the Northern California Fire Science Consortium hub
Home and landscape design considerations for wildfire, prescribed fire, forest health and prescribed fire, wildfire and fuels in redwood, Douglas-fir and tanoak forests, fire education
UC Cooperative Extension forestry/fire science and natural resources advisor
Sutter, Yuba, Butte and Nevada counties
Fire ecology and management, fuels treatments and fire policy
- Author: Jeannette E. Warnert
One focus of UC Agriculture and Natural Resources (UC ANR) is forestry, and a host of its researchers study the impacts of fire and fire suppression in California wildlands. This expertise is valued by the public and the news media in times when wildfires strike.
The 2017 fire season has been the most severe on record, due to a combustible combination of drought, rains, and especially, wind. “What really makes big years in terms of acres burned is essentially how many really windy days we have,” UCCE forestry specialist Bill Stewart told KPCC. Last year's wet winter, which led to increased vegetation, and this year's record-breaking heat waves aren't as indicative of fire danger as Santa Ana winds, known in Northern California as Diablo winds, Stewart said. “It's always dry. There's always fuel,” he said.
UC Cooperative Extension specialist Max Moritz said the state needs to incorporate wind corridors into its fire hazard severity zone maps, according to an article on ScienceMag.org. Stricter building codes apply in places designated as high-risk.
UC ANR scientists also generate local fire recovery and mitigation resources for the public in wildfire-prone counties.
Links to all the sites have been aggregated on a UC ANR story map - https://arcg.is/0SWyW8. This story map may be freely shared on websites and social media. (Find the share URL and the embed code by clicking the share icon on the upper right hand corner of the story map.)
Local UC Cooperative Extension fire resources websites listed on the story map are:
The following general information on wildfire recovery is available for those who were directly impacted by the wildfire.
Don't get burned twice (pdf)
The site also provides information for those whose homes were spared in 2017, but now wish to take precautions to reduce the risk of wildfire damage in the future.