Vineyard fires burn bright in freezing cold of Burgundy night

By Monica Bielanko, AccuWeather senior producer

In the evening, when the sun is slipping below the horizon, there's often nothing better than dropping a needle on a record, sitting on the porch and enjoying a glass of wine. For some, it's all about a bold and spicy Cabernet Sauvignon, while others are passionate about chilled Chardonnay with zings of citrus.

Whether red or white or rosé, it all comes from grapes. Growing grapes, like most everything else planted in the ground, is a delicate dance with Mother Nature and when she takes the lead, it's hard work keeping up. Spring frost is a threat that has the potential to destroy an entire crop of grapes before it even begins. During winter, vines are dormant. They are frost hardy and can easily survive temperatures from 14 degrees Fahrenheit to as low as 5 F, according to Wine Enthusiast. However, the situation changes dramatically once buds sprout their first green shoots. Frost damage happens when temperatures drop below 32 F. Buds and shoots have water inside so when they freeze, the tender cell walls burst.

As Vitisphere.com reports, following a frost alert on April 14, winemakers of Chassagne-Montrachet lit fires and heaters to fight the frost. As temperatures only dropped moderately below 32 F and the humidity was relatively low, damage was limited.

Winemakers trying to limit frost damage on their vines employ a variety of heating techniques to keep their crops warm. Some, like Chassagne-Montrachet, light big oil drums throughout their vineyards, others use 'bougies' -- large paraffin candles that give off heat. 

Vintners at Chassagne-Montrachet in Burgundy, France, set fires in their fields on April 14, 2019, to counteract the effects of frost on their vines as a cold snap swept the area. (Ju Berno via Storyful)

"Our vineyard team stays up overnight, constantly checking the weather stations for sign of a frost and when the temperature does drop, they must quickly head out to the vineyard to light the bougies," Hannah Simpson-Banks tells Decanter.com. The candles generate enough heat to keep frost at bay and have the added bonus of creating protective smoke.

"The smoke doesn’t allow the warmth from the ground to rise," Dr. Herwig Jamek, a winemaker in Austria says. "Nor can the freezing air sink down and damage the vines. The fires create just enough smoke to cover that critical period."

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Although it sounds counterintuitive, some commercial vineyards run sprinklers through the night. This causes water to freeze over the tender buds. Wait, what? To protect grapes from frost, growers coat them with ice? They do! The science behind it is somewhat difficult to understand, but winegrower, David Ruzzo, breaks it down like this for Winemaker: "First think about what happens when ice melts. In order for water to make the transition from solid to liquid -- in other words, in order to melt ice -- energy must be added to the ice. This energy comes in the form of heat. Once the ice is melted, the resulting water contains that energy. Now, in order to reverse the phase transition -- in other words, to freeze water -- the water must give up that energy. The amount of heat generated is small, but enough to get trapped between the green tissue and the ice and keep the vines protected as long as it doesn’t get too cold (below 28 F/minus 2.2 C on average) or stay cold for too long (more than a few hours)." Accurate weather forecasts are crucial when it comes to fighting frost.

Ruzzo says the technique has worked for him every time he's done it over more than eight years of growing.

There's a lot more that can be done to minimize frost damage, including growing grape varietals that match your climate and specific pruning techniques. Using fans and wind machines to keep the air moving also helps to prevent frost. Some enterprising growers, like Andrew Donaldson, a grower in New Zealand, utilize helicopters that fly low overhead, keeping the air moving. “The chopper pilot finds the inversion layer and hovers around just under it, forcing warm air to circulate back down to the ground, keeping the frost at bay," he tells Wine Enthusiast. "We have temperature sensors in each vineyard block that change color. The pilot watches these sensors and moves across the vineyard. It’s very effective for us.”

Growers in Burgundy, where the most recent frost occurred, are taking no chances after what's been called the region's 'worst frost in more than 30 years' hit some areas three years ago, drastically impacting the 2016 and 2017 harvests. As Decanter.com reports, on the night of April 26, 2016, a severe frost swept across Burgundy vineyards. "Such a frost is unseen since 1981," Caroline Parent-Gros, of Domaine AF Gros in Pommard, said at the time. But she, like all growers, takes the weather in stride. "Mother Nature decides; we have to live with that and this is the risk of our job."

So the next time you're kicking back, enjoying a glass of delicious wine, offer up a toast to all of those whose hard work created the perfect grape for your enjoyment.