This past summer was the smokiest on record in B.C. Environment Canada estimates that parts of the Interior, including the Okanagan wine country, experienced the worst visibility on record — as many as 400 hours of low visibility some areas, or close to 18 per cent of summer hours.
Degree of visibility indicates how much particulate matter is in the air. Low visibility occurs when it becomes difficult to see 10 kilometres into the distance.
But even months after rain and snow have washed smoke from the air, the smoke will linger. Eau de char will perfume the ground and trees in burnt areas when the snow melts. It might even show up this year’s vintage from the Okanagan’s vineyards.
When a vineyard is exposed to smoke, the grapes’ skins, leaves and vines absorb volatile phenols, a class of chemical compounds found in woodsmoke.
The grapes taste fine when eaten, but wine made from the grapes might taste awful. Wildfire-affected wine can taste of ashtray, smoke, leather, burnt, barbecue, smoked meat, bacon or salami.
Until recently, “smoke taint” wasn’t easily detected until after fermentation — too late for winemakers to adjust their processes to reduce the unpalatable outcome.
But B.C. researchers have devised a technique that allows growers and vintners to assess smoke damage to their grapes.
The test “detects the exact amount of volatile phenols present in the grape,” says Wesley Zandberg, one of the researchers and a professor at the University of British Columbia. “There’s no need to ferment them first, and we get results within a matter of hours.”
Wine producers currently use a subjective measure in which they take small batches of grapes, ferment them, then taste the resulting wine to determine whether it has the telltale burnt, smoky flavour. The sample ferment takes up to 10 days and is labour- and cost-intensive.
In addition, during the delay, grapes left on the vine to ripen while the tests run their course could be exposed to yet more smoke. In 2003 — a bad wildfire year in Kelowna — that delay meant one area vineyard had to pour out its entire vintage because of smoke taint.
The new tool offers a faster and more precise way to help vineyards and wineries manage the risk from smoke exposure.
By knowing precisely whether and by how much each crop has been impacted by smoke exposure, Zandberg says growers and winemakers alike can make informed decisions about whether the grapes should be used or abandoned.
Red wines are more at risk of being smoke-tainted. Red wine is made from juice left in longer contact with the grape skins than juice used to make white wines. That longer contact period means more of the smoke molecules seep into the juice.
Hints of smoke are often desirable in wine — they add complexity and depth to great vintages. Many wines are aged in smoked oak barrels to achieve those smoky, leathery, barnyard-y hints.
However, “smoke taint” itself isn’t subtle. Reports suggest that not even diluting or blending can hide its overpowering taste.
Zandberg says the new test can also be applied after the grapes have been fermented and aged to add precision and accuracy to the winemaking process.
“This could be hugely beneficial in helping winemakers determine whether wines have enough smoky compounds to match their desired flavour profile after aging in smoked barrels,” he says.
Every kilogram of wood burned releases up to 27 grams of volatile organic compounds in smoke. The volatile compounds include benzenes, formaldehyde, formic acid, methyl chlorides, naphthalene, chlorinated dioxins, polycyclic aromatic hydrocarbons and many other chemicals. Some are highly aromatic phenols, providing the campfire, fried-bacon, cured-leather smell that we know so well from sitting around the campfire and roasting marshmallows.
Those aromatic smoke molecules are the ones that concern B.C. grape growers.
Amount of smoke, the time and duration of exposure of the vines to the smoke, the stage the grapes are during exposure, the ripening process, variety of grape, and how often the grapes are exposed in one season affect the amount of volatile phenols absorbed by the grapes.
