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Smoke flavour hides in wine grapes


VANCOUVER—Smoky overtones can ruin a nice bottle of wine, but researchers in British Columbia are finding that preventing grapes from capturing the flavour of wildfires can be difficult.

Wine grapes absorb smoke compounds, surrounding them with sugar, explained Wesley Zandberg, an assistant chemistry professor at the University of British Columbia in Okanagan.

The chemicals—known as volatile phenols—can't be detected when you eat or smell the fruit. But during the fermentation process, yeast cuts the sugars off, releasing flavours and smells that aren't necessarily pleasing to the palate, he explained.

“It wouldn't be a problem if smoky-flavoured compounds got stored in grapes, and they just kind of hung out there and I could never taste them,” Zandberg said.

“I can eat the grapes, I can test the grapes before fermentation, they taste great, they smell great,” he noted.

“And then as soon as I put the yeast on them, I find that I've got terrible-tasting wine.”

Zandberg and his team did field testing in B.C.'s wine region, an area in the Okanagan that's also susceptible to wildfires.

The researchers built a structure over some grapes and pumped in smoke, simulating the burning of foliage that grows in the region.

Then they compared the composition of the smoky grapes to fruit that grew on a nearby vine, free of smoke.

Zandberg said his team found the grapes absorb the smoke quickly, within about an hour, and can't be stopped by washing the grapes with water.

That makes it hard to protect the fruit from wildfire smoke, he said.

The findings were published this month in The Journal of Agriculture and Food Chemistry, but Zandberg said the researchers still are looking at how the data can be used.

Now the team wants to look at how their work can alert wine-makers to a smoke-tainted crop.

“We're interested in connecting the chemistry with the sensory analysis,” Zandberg explained, noting the earlier a grape producer knows their fruit has been compromised, the earlier they can take action.

“They don't have to pick these things at risk, pay everybody to pick them, then find that they have a ruined crop,” he noted.

“They can have an answer well before that.”

In 2003, fires in the Okanagan left some vineyards scorched and others steeped in acrid smoke that ruined grapes.

Thankfully, the effects only last a single season, Zandberg said.

“Once you pick the grapes and then they grow again the next year, there's none of that smoke left anymore in those grapes,” he remarked.

Last summer saw record-setting wildfires burn across a large swath of B.C. Smoke left many communities in the Interior socked in for days—and even weeks—at a time.

But Zandberg said there's no indication the vineyards have been compromised. The smoke wafted in from large distances, which appears to make the compounds that effect the grapes less potent, he noted.

“We really don't detect much of anything in the grapes [from 2017],” he said.

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