Forest fires have sometimes reached the vineyards directly, although fortunately this is not a common situation. What's more, vine crops act in many cases as firebreaks, limiting the spread of flames in bordering wooded areas.
But the detrimental effects of forest fires on grape growing and wine production go far beyond burning vines. Although the problem is not well known in Spain at a popular level (experts are on the case, of course), the smoke from forest fires can reach the vines and leave ashes and chemical residues that harm the quality of the wines produced with these fruits.
Smoke taint (smell of smoke) is the term used by winemakers, oenologists and biochemists to refer to the smell and taste effects caused in wine -and it can also be in cellars and the like- by the various compounds from the smoke that has affected the vines. These collateral damage from forest fires have been studied in great detail for years in countries and regions especially affected by this problem, such as California and Oregon, in the United States; Chile and Australia.
The most outstanding advance in this specialty has been published this week by experts from Oregon State University, in Covallis (United States) and Washington State University, in an article in the Food Chemistry Advances magazine with this descriptive title: " A combination of thiophenols and volatile phenols cause the ashy taste of smoke odor in wine."
In this work led by Professor Elizabeth Tomasino, a new class of compounds that contribute to ashy or smoky flavors in wine made from grapes exposed to smoke from forest fires has been discovered. This development is significant for winemakers who have struggled to combat the impact of smoke on grapes at a time when climate change is causing an increase in the number and severity of wildfires, the researchers said. Oregon State University.
Elizabeth Tomasino, associate professor of oenology at this public university, highlights that "these findings provide new avenues for research to understand and prevent smoke odor in grapes." On the other hand, says Tomasino, this research "will also help provide tools for the grape and wine industries to quickly make decisions about whether to harvest grapes or make wine after a smoke event."
Forest fires are a significant threat to wineries because persistent smoke exposure compromises the quality and value of wine grapes and negatively affects wines. That threat is particularly pronounced on the West Coast of the United States, where California, Oregon and Washington are three of the top four wine-producing states in the country.
Using smoke-contaminated grapes to make wine can affect the aroma and flavor of the wine. Traditionally, changes in flavor and aroma have been attributed to a class of compounds known as volatile phenols. However, volatile phenols were not considered to be good predictors of smoke odor problems, Professor Tomasino has now noted. For example, wines with high levels of these compounds often did not taste smokey, and wines with low levels could taste smokey, recalls the oenology researcher.
Elisabeth Tomasino and Jenna Fryer, a PhD student in the former's lab, published a paper in 2021 outlining a new standard for identifying the smoky/ashy component of smoke odor in wine.
As part of that work, they discovered a new class of sulfur-containing compounds, thiophenols, which are not normally found in wines and spirits. Some thiophenols may be present in grilled or barbeque-cooked meat and fish, and previous sensory research has used the terms meaty and burnt to describe them.
To better understand what impact thiophenols could have on wine, Cole Cerrato, a researcher at this same Oregon university who works closely with Tomasino, conducted an experiment in the center's experimental vineyard. The researchers also built a greenhouse-like structure, placed it over a row of grapes, and exposed the grapes to smoke. They later harvested those grapes and made wine from them.
The wines the researchers made were sent to Tom Collins, an assistant professor at the Washington State Wine Science Center. The team confirmed that thiophenols were found in wines that had been exposed to smoke at the Oregon State University vineyard, and no thiophenols were found in control samples that had no smoke exposure.
During sensory analysis in Tomasino's lab, wines exposed to smoke at the Oregon State vineyard, which contains both thiophenols and volatile phenols, were described as ashy and smoky.
"To date, volatile phenol concentrations and frequent tasting of potentially affected wines are the only predictors that winemakers can use to determine how smokey their wines might be," recalls Elisabeth Tomasino. "The discovery of thiophenols provides a new chemical marker for smoke odor that could provide a reliable way to identify smoke odor and ways to potentially eliminate it during the winemaking process."
