Temperatures soared across the Pacific Northwest in June this year, and the heat wave lingered in Idaho for a good chunk of the summer. National Weather Service data showed the Treasure Valley in southwest Idaho—home to two of the state’s American Viticultural Areas (AVAs)—had the hottest summer on record. And the heat affected the Lewis-Clark Valley AVA in the northern part of the state as well.
“During bloom time, it was about 100 degrees, so bloom went really fast,” said Vince Hewett, assistant winemaker at Rivaura Vineyard near Julietta, Idaho. He said they saw consistent 100-degree weather for close to a month in June and July.
When temperatures rise above 95 degrees, vines slow down and go into heat stress mode to conserve their water. This slows down photosynthesis and slows the development of sugars in the fruit. The answer is more water, and Idaho grape growers pulled out all the stops.
“Early on in the growing season, when (the vines) were just getting started, we gave them all the water they needed and could want,” Hewett said.
The hot weather meant budbreak happened earlier this year for some vineyards, and harvest started and ended sooner. For Skyline Vineyards outside Caldwell, Idaho, Viticulturist and Vineyard Manager Jake Cragin reported harvest began in late August this year, nine days earlier than in 2020, and was wrapped up in October—unhampered by any early frosts.
Smaller Berries, Smaller Yields
Idaho vineyards reported yields were down slightly due to the heat.
Skyline’s yields were down 12 percent overall, according to Cragin. Mike Williamson of Williamson Orchards and Vineyards reported yields were down on young blocks of vines. “They seemed to struggle with the heat more than the older vines,” he said.
Martin Fujishin of Fujishin Family Cellars agreed the impact was inconsistent. “Some of our red varieties have a very, very light crop load. And some of the white varieties or some of the earlier reds have a much heavier crop load. So we have a lot of variability in the size of crop coming in for each variety, which is kind of the name of the game on a hot year.”
Intense Color and Flavor
There is a marvelous silver lining for Idaho winemakers.
“We had the same number of clusters we would for a normal year, but the size of the berries on those clusters was much smaller. And that means more skin contact for the wines, which means more color intensity, and in many cases, more flavor intensity,” Fujishin said.
Vince Hewett from Rivaura said winemakers like to call it a “higher skin to juice ratio” which means the surface area of the grape is higher in proportion to the contents inside. “That’s where all the yummy flavors and aromas are at in the grape,” he added.
Hewett said because of the smaller berries, Rivaura was seeing some of the best fruit quality they’ve ever had. “Tasting at the press, the wines are tracking to be an awesome vintage,” he said.
Fujishin summed it up. “A lot of the work is already done for us,” he said. “We’re going to have bright, intense flavors, and our job is not to mess it up.”
Moya Dolsby, Executive Director of the Idaho Wine Commission, praised how growers across the state responded to this summer’s heat. “Idaho’s grape growers are resilient,” she said, adding the issue of warmer temperatures is not going away.
“This season gave us a wealth of knowledge about growing grapes in these conditions,” she said.
Hewett of Rivaura agreed. “It’s something we’re going to have to face in the future.”
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