Chemical Analysis Reveals of Wildfires' Effects on Grapes and Wine

Chemical Analysis Reveals of Wildfires' Effects on Grapes and Wine ...

As the wildfire season in the West rises in length and severity, it is putting an end to the wine industry''s quality. Volatile compounds in wildfire smoke can be absorbed by grapes and produce an unpleasant taste known as smoke taint in wine grown from affected grapes.

A new study led by UC Santa Cruz provides valuable information and guidelines for identifying grapes and wines affected by the smoketaint. Published on March 3 in the Journal of Natural Products, the study is based on an analysis of more than 200 grape samples from 21 grape-growing areas in California and Oregon.

Phil Crews, a leading research professor of chemistry at UC Santa Cruz, has owned and operated a small winery (Pelican Ranch Winery), whose extent he discovered the smoke taint danger in the aftermath of the 2018 Mendocino Complex Fire, where large wineries began to reject grapes from the affected area and Crews was retained as a consultant by legal firms representing wine professionals.

According to me, adequate analytical data was inadequate to determine if grapes or wines were affected by the smoke.

Crews found that the best research on the problem had been done at the Australian Wine Research Institute (AWRI), where researchers had identified a spectrum of compounds that could be detected in affected grapes and wines and used as biomarkers of smoke taint. He found that most European laboratories in the country were inadequately measuring their results. He also found that grapes and wines from California and Oregon were excluded from the study.

Eleni Papadakis, a winemaking consultant based in Portland, Oregon, said this research is extremely valuable, with the potential to save thousands of dollars, and is increasingly relevant in our dealings with drought and climate change. I believe I speak for the entire winemaking community when I express my gratitude for Professor Crews'' hard data and evidence-based guidance.

Crews'' approach focuses on the direct measurement of smoke-derived compounds in the form in which they are stored in the grapes. Previous studies have found that smoke taint is associated with volatile phenols present in smoke from burning vegetation. These compounds are absorbed through the skin of ripening grapes and accumulate in the grapes, where they become bound to sugars to form nonvolatile compounds called phenolic diglycosides.

The phenolic compounds are not intended to be smelled or tasted, but the foul-tasting free phenols may be released by enzymes, either during the wine fermentation or in the mouth by enzymes or bacteria present in saliva.

During bottle aging, the phenolic diglycosides are stable in cabernet sauvignon, but then the monomers that smell bad are released in the mouth, according to Crews.

According to Crews, it is important to direct measure the bound phenolic diglycosides. These large compounds are not readily detected with the standard methods used to analyze aroma and flavor compounds in wine (gas chromatography/mass spectrometry, or GC/MS), but they can be measured using more sophisticated methods (ultra-high-performance liquid chromatography, or UHPLC, and quantitative mass spectrometry).

The study examines some of the first quantitative measurements of phenolic diglycosides in premium California and Oregon grapes and wines from 2017 to 2021. These results include baseline data for normal grapes, as well as grapes exposed to six different levels of natural wildfire smoke.

Six biomarkers endorsed by AWRI as the representative of compounds associated with the smoke tact, according to the latest findings. Two of the biomarkers tested were non-util, according to Crews.

Further research is needed in order to improve our understanding of these compounds. Those areas could be used today to examine a bottle of wine or a batch of grapes and see if it will be caused by a smoke taint.

Crews, a commercial testing facility in Santa Cruz, has the experience and equipment needed to perform the analyses on a large scale.

Crews also reached out to Ryan Keiffer and Glenn McCourty of UC Cooperative Extension in Mendocino County, who provided samples of grapes and wines for testing, and are both coauthors of the paper. Paul Dorenbach and Itzel Lizama-Chamu of UC Santa Cruz, and Erin McCauley of California State University, Dominguez Hills.

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