Winemakers use flames to fight frost during temperature drop

Winemakers in France fought frost with fire when a drop in temperatures threatened grape crops this week. It's a stark contrast to temperatures over the winter with some areas in Europe, including much of France, experiencing their warmest winter on record.

"Temperatures in much of France from Dec. 1 through April 17 have averaged 5 F above historical levels," AccuWeather Senior Meteorologist Alex Sosnowski said. "The warmth that followed a brief chilly episode from early April has pushed temperatures to 5-10 F above average this month and has further advanced bud break, sprouting and blossoming."

Winegrowers warm themselves around a fire as anti-frost candles burn in a vineyard to protect blooming buds and flowers from the frost, in Chablis, Burgundy region, Monday, April 4, 2022. Plunging April temperatures around France are threatening vineyards and other important crops. Vintners are scrambling to find ways to protect the vines from the frost, which comes after an unusually mild winter and is hitting countries around Europe. (AP Photo/Thibault Camus)

While clouds and breezes may limit the extent of frosts and freezes this week, there is the potential for a couple of nights when skies become clear, winds drop off and temperatures plummet in parts of the vineyard and orchard areas, including in France, Germany and Spain.

To protect his grapes, Jean de Saint Venant, who owns a vineyard in the Loire Valley, lights bales of hay and straw on fire to create a smokescreen that, he said, is like "sunglasses for the vines." The layer of smoke protects the vines from sudden changes in temperature as the sun rises following a cold night and prevents a thaw from happening too quickly.

Dr. Herwig Jamek, of Weingut Jamek in the Wachau Valley of Austria told Wine Enthusiast, "During a radiation frost, that smoke acts like artificial cloud cover." The smoke doesn't allow the warmth from the ground to rise or the freezing air to sink and damage the vines, he said. The fires create just enough smoke to cover the critical frost period.

Spring frost is a threat that has the potential to destroy an entire crop of grapes before the fruit even emerges. 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.

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.

Young inflorescence of grapes on the vine close-up. Grape vine with young leaves and buds blooming on a grape vine in the vineyard. Spring buds sprouting

Protecting grape vines from low-temperature injury has been occurring for thousands of years. According to a report from the U.S. Department of Agriculture, "It began at least 2,000 years ago when Roman growers scattered burning piles of prunings, dead vines and other waste to heat their vineyards during spring frost events." The USDA estimates that as much as 15% of the total world crop production is affected by cold weather injury every year.

Leftover white grape on a tendril with lots of ice crystals

Winemakers employ all kinds of techniques, from helicopters to massive fans and heaters, to salvage crops because frost can devastate vineyards in a single night. A historic freeze just a few years ago is at the forefront of the memories of many vineyard owners.

In 2017, vineyards from Champagne, Bordeaux and Burgundy were dramatically affected when temperatures dropped below 19 F in all three of those areas. Shoots that had already begun to develop were destroyed. Julien Hubail, the expert at the Bugey Wine Union, told The Guardian that the historic frost in 2017 was the worst any of the winemakers can remember witnessing.

Winemakers are in for a break toward the end of the week with wintry weather and showers expected to taper off in the United Kingdom and into France, according to AccuWeather Meteorologist Adam Douty.

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