MARCH 2018• COUNTRY LIFE IN BC UBC perfects test of smoke taint in wine grapes Hot, dry summers in the
Okanagan are perfect for growing grapes but with that weather can come the threat of destructive wildfires. Even if vineyards escape the actual fire, the fruit is still at risk of smoke that can do extensive economic damage. The
Research by MARGARET EVANS
problem is made all the more complicated by the fact that a vineyard owner may not know the extent of crop damage until after the time and expense of harvesting and fermenting. Until now. Researchers at UBC
Okanagan have developed an analytical test to accurately measure the amount of volatile phenols from smoke in the fruit before wine production. Volatile phenols are aromatic chemical compounds and they are one of the key molecules responsible for defects in smoke-exposed grapes. But these defects don’t surface until the fermentation process. “When the grape is
ripening, there are a lot of different sugars and what the enzymes in the grapes do is take these sugars and attach them to the volatile phenols,” says Dr. Wesley Zandberg, assistant professor of chemistry. “The effect is that the volatile compound we could perceive [as smoke] is now not volatile at all and we can’t smell it and we can’t taste it and we can’t detect it.” In other words, we don’t
know it’s there. He says that, at harvest
time, grapes may taste fine and a vineyard owner might hire, say, 60 people to work 24 hours a day for two weeks to pick tons of grapes. They are then crushed and fermented, but two weeks later all that is produced is a foul-smelling wine. The trigger is the yeast.
During fermentation,
the yeast possesses the enzymes that can cleave the sugar from the phenols and they
regenerate the smoky flavour that was previously masked. “Until now, detecting these
smoky compounds in grapes required fermenting a small sample over at least ten days and relying on subjective measures like taste and odour,” says Zandberg. The challenge of doing a small testing batch is that harvest is held up for the two weeks that the test grapes are fermented. Meanwhile, grapes ready for harvest may rot on the vine. If they are picked and held, they will start to ferment on their own. “We’ve developed a test that detects the exact amount of volatile phenols present in the grape,” Zandberg explains. ”There’s no need to ferment them first and we get results within a matter of hours.” In the 2017 study, the
research team exposed grapes growing in a plastic enclosure to smoke from burning Ponderosa pine, the main fuel source in the Okanagan. Next to them were unexposed grapes that were the controls. The team tracked the growth and ripening process as smoke from a commercial fish/meat smoker was funneled via tubing into the plastic
enclosure. A laptop computer was connected to sensors inside the enclosure to monitor smoke density, humidity and temperature. The big problem about
grapes exposed to smoke is that, while ash can be washed off, smoke cannot. It’s not well understood yet exactly how the grapes absorb smoke but it’s believed that most is taken up through the berry and the leaf where it ‘sits’ in the sugar- bound form until fermentation. “What really motivated us
is that we can create a test that can discover these sugar- bound forms in grapes before fermentation and make an accurate risk assessment of what the wine will taste like based on those values” he says. “These volatile phenols are immediately trapped in grapes and we’ve
demonstrated that, within less than 24 hours, they are linked to sugars so they are not perceptible by smell anymore. They are hiding. But the fact that they don’t change [once in the grape] means we can at any point after smoke exposure reliably quantify how much is there.” Each year can bring the potential for smoke damage from wildfires. The worst year was 2003. In 2015, some vineyards near Oliver were affected by smoke from Washington State fires. In 2017, while wildfires were devastating in the Chilcotin region, Zandberg says the smoke reaching Okanagan wine country was all high
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A commercial fish/meat smoker was used to funnel smoke into plastic enclosures covering grape vines. UBCO PHOTO
smoke and old smoke and did not pose a problem. Smoke effects only last one season and the vines will grow healthy fruit the following year.
The research team is now planning the 2018 studies. With a better understanding of the biochemistry of the grape, they are looking at a
variety of approaches to help wineries mitigate smoke exposure problems.
The study was published in
the Journal of Agricultural and Food Chemistry and was supported by funding from Mitacs, the Natural Science and Engineering Research Council and the BC Wine Grape Council.
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