KELOWNA, B.C. — Wildfire smoke is absorbed quickly by wine grapes, can remain long after the smoke has cleared and even when grapes taste normal, researchers at the University of British Columbia’s Okanagan campus say.
They also have devised a tool to help growers determine levels of smoke taint in grapes and whether a crop is worth harvesting or not.
A recent UBC and Supra Research and Development study determined that volatile phenols — chemicals in smoke that can give wine an off-putting smoky flavor and aroma — are absorbed quickly in grape skin and remain.
Wesley Zandberg, assistant professor of chemistry at UBC-Okanagan, says the biology of how wine grapes respond to smoke has been poorly understood.
“Winemakers know that grapes grown in smoky conditions can lead to smoky-flavored wine although the grapes themselves taste normal. How or why this happens has largely remained a mystery,” he said.
Zandberg and his team collected samples of Cabernet Franc grapes after exposing them to simulated forest fire smoke. They tested for volatile phenols at several intervals after exposure to smoke from local fuels including Ponderosa pine and in wine made from the same grapes.
“We found that once the grapes were exposed to smoke, the volatile phenols were rapidly metabolized by the grape and stored, in part, in a sugary form that we can’t taste or smell,” said Matthew Noestheden, UBC doctoral student.
Concentrations remained unchanged in grapes and could only be detected when grapes were fermented into wine, he said.
The team found that washing grapes, to simulate overhead sprinklers to mitigate smoke, did not alter concentrations of volatile phenols.
The researchers also developed a new analytical test to precisely measure the amount of volatile phenols in grapes prior to wine production.
“Until now, detecting these smoky compounds required fermenting small samples over at least 10 days and relying on subjective measures like taste and odor,” Zandberg said.
Results can be realized in hours and help growers make informed decisions about whether to harvest grapes or not, he said.
Zandberg also said many wines are aged in smoked oak barrels that contain volatile phenols to give desired flavor. He said the testing can be done after fermenting to determine if wines have enough smoky compounds.