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In California’s Napa Valley, cabernet sauvignon is king.

The bold red wine has made the region world famous, with some bottles retailing at hundreds of dollars. But increasingly severe heat waves are taking a toll on the grape variety, especially in late summer during ripening. As temperatures keep rising, the wine industry is slowly confronting a future where Napa may not be the prime cabernet region it once was.

In the face of climate change, wineries around the world are innovating. New technology is being installed to keep the grapes cool during heat spells. A handful of wineries are going a step further. They’re experimenting with new grapes, ripping out high-value cabernet vines to plant varieties from hotter climates.

The goal is to find heat-tolerant grapes that blend well with cabernet, potentially making up for the flavors that cabernet could lack when temperatures get even hotter. While many bottles labeled cabernet are already blended with other grapes in small amounts, winemakers may need more flexibility in the future.

“We know we have to adapt,” says Avery Heelan, a winemaker at Larkmead Vineyards in Calistoga, Calif. “We can’t just pretend that it’s going to go away, because all we see is each year it’s getting more and more extreme.”

Still, blending with other grapes comes with risks. For a U.S. wine to be labeled cabernet, a bottle must contain 75% cabernet grapes or more. Any less, and it’s considered a red blend. Blends typically don’t command the same prices on store shelves as cabernet, especially since consumers are accustomed to picking U.S. wines by the name of the grape. Moving away from cabernet would be a major financial gamble for Napa’s multibillion-dollar wine industry.

“It is a big shift,” says Elisabeth Forrestel, an assistant professor of viticulture and enology at the University of California, Davis. “Without the market changing or demands changing, you can’t convince someone to grow something that doesn’t sell or doesn’t garner the same price.”

University of California, Davis research assistant Jacob Vito crushes cabernet sauvignon grapes from Napa Valley to analyze their chemical compounds. The lab is studying how heat is affecting the grapes.

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Charbono, anyone?

Some grapes growing at Larkmead Vineyards aren’t ones that many American wine drinkers would recognize. Long rows of vines are labeled: touriga nacional, aglianico, charbono and tempranillo.

“There’s not a huge market for a lot of these varieties,” says Heelan, walking among the vines on a hot summer afternoon. “We’re really choosing them not from popularity, but for their qualities.”

Established more than a century ago, the winery is known for its bottles of cabernet sauvignon. These lesser-known grapes were planted only a few years ago, part of a research vineyard that took the place of cabernet vines.

“Which most people would probably think is a little crazy, considering it’s 3 acres of perfect cabernet land,” Heelan says. “But certainly with the climate and how dramatically it’s changed over even the last 10 years, we really have to start adjusting.”

Winemaker Avery Heelan is growing several rare grape varieties at Larkmead Vineyards in Napa Valley, in the hope that they’ll blend well with cabernet grapes as temperatures get hotter.

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The vineyard is already at the hotter northern end of Napa Valley, but the extreme heat in recent years has been a wake-up call. A late-summer heat wave in 2022 hit temperatures just under 120 degrees at the vineyard, she says.

“When it gets that hot, the vines, they’re done,” she says. “They’re going to go dormant, and when that happens, they’re not ripening anymore.”

In extreme heat, cabernet grapes can lose their rich color. They also dehydrate, wrinkling like raisins, which produces wines that are sweeter and more alcoholic. Heelan says the grapes that the vineyard is testing could provide an added boost of color or acidity to cabernet, helping balance out the wine when temperatures take their toll.

The experiment has its cost. In addition to the lost revenue from removing cabernet, grapevines take up to five years to produce their first crop, plus several more years for the wines to ferment. Heelan says only then will they start to see how the new grapes are performing. But the goal is to prepare the winery for the future, knowing that heat will likely get worse.

“Honestly, the more we experiment and learn about how to adapt, I think the wines are just getting better and better,” she says.

In hotter temperatures, cabernet grapes lose their rich red color and produce sweeter, more alcoholic wines.

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Where cabernet is king

Farther south, Shafer Vineyards sits in the heart of Stags Leap, a Napa wine region that’s known for high-end cabernets. Winemaker Elias Fernandez says the grapes benefit from a cool evening breeze that blows in from San Francisco Bay.

This summer, heat has already been a problem. July was the hottest July on record in California. Fernandez points to a grape cluster where small green grapes are nestled among larger purple ones.

“This is effects of the heat,” he says. “It’s not maturing, so this is where you lose some fruit.”

Winemaker Elias Fernandez is installing new technology at Shafer Vineyards in Napa Valley to combat heat waves.

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The damage isn’t too widespread this year, unlike in 2022. But with summers getting more intense, Fernandez says the winery is looking at technology to help the cabernet vines. They’re currently installing misters, which spray water into the air to cool the temperature.

“It’s a constant mist,” he says. “How many of you have been to a party where they have misters? Doesn’t that feel good? Well, that’s what the vines are feeling.”

Still, using extra water is a challenge in drought-prone California, he says. Plus, the water droplets can concentrate the light on the grapes and burn them, so misters must be run until the sun sets to keep the droplets from collecting. But Fernandez says he’s hoping the misting will keep the cabernet vines producing at the highest level.

“I think the first thing we’ll be doing is mitigation, hoping to keep it as the true varietal of Napa Valley,” he says. “That’s what we’re trying to do — is buy time and see what happens with this whole thing.”

For now, he’s not considering planting other grape varieties. With wines that are priced at $100 and up, cabernet is central to their business.

“For me, it’s hard to think that people are just going to throw cabernet out the door and plant something else,” he says. “I really do. It’s the king of the wines of the world.”

To keep producing high-quality cabernets, Napa Valley winemakers may need to blend them with other grapes to balance out the effects of heat. But wines labeled as blends, instead of cabernet, often sell at lower prices.

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Wine regions are shifting

Professor Elisabeth Forrestel is studying how Napa’s wine regions are shifting with climate change.

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Elisabeth Forrestel is one person trying to understand the big swings in the temperature. In her lab at UC Davis, her research team is smashing Napa Valley grapes inside plastic bags. They’ll be analyzed at the molecular level to see how they change during the summer.

Forrestel’s lab is gathering wine grapes from Napa Valley throughout the growing season, along with detailed temperature data, to see how the most crucial compounds for wine are affected by heat. Studies show the average temperature during the last 45 days of the growing season in Napa — when grapes ripen— has already warmed almost 3 degrees Fahrenheit from 1958 to 2016. But it’s the intense heat waves that do the most damage to molecules that produce a wine’s color and aroma.

“When you have these extreme heat events, you can have a lot of impact on the development of that flavor profile,” she says. “If it was just an average change, it would be a lot easier to manage.”

Forrestel is working on updating a central guide for winemaking, known as the Winkler Index. Developed in the 1940s, it shows the ideal locations to grow different varieties of wine grapes, based on how much heat they receive. Napa Valley was originally indexed for cabernet sauvignon, but this could shift as the climate gets hotter.

With cabernet being the world’s most widely grown wine grape, cabernet vines are resilient to different temperatures, Forrestel says. It’s a question of whether Napa winemakers may need new strategies to keep it producing at such a high-quality level. Since grapevines last 50 years or more, winemakers are faced with making planting decisions today that will need to withstand a hotter future.

“Some of the paradigms in what you would plant need to shift,” she says. “People need to have different approaches so there can be more resilience and you can have more options.”

UC Davis research associate Martina Galeano prepares grape samples. Wine grapes need heat for ripening, but too much heat can break down some of the crucial compounds for wine flavor and color.

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Would you pay the same for a blend?

Blending cabernet with other red grapes could be one strategy. But since U.S. regulations require any bottle labeled cabernet to contain 75% cabernet, at some point wineries may be looking at changing their labels to say “red blend.”

“We have a perception that a blend is not as high quality as getting that high-quality cabernet, and they’re not on the same price point, so it is a big shift,” Forrestel says.

The challenge is particular to U.S. winemakers, since many other countries label their wines by region, instead of grape. The famed red wines from Bordeaux in France are already a mix of six grapes, including cabernet, so winemakers have more flexibility. Winemakers there have also struggled with heat, so French authorities recently approved four more red-grape varieties for blending. Since the wines are labeled with Bordeaux, wine drinkers may not even notice the shift.

Wines in the U.S. are generally labeled by the grape variety, a system that was promoted when the domestic wine industry was growing in prominence decades ago. In an effort to compete with wines from Europe, some thought focusing on the grape variety would demystify wines for consumers and show the quality of American wines.

Now, that system may work against them. Cabernet sauvignon is the most popular red wine in the U.S., according to NielsenIQ. So Forrestel says consumers are also part of the solution by creating demand for wines that are better suited for a hotter climate.

“Be open,” she says. “Because I think it’s really easy to walk in and buy what you’re used to. And also, trust what you like and not what you’re told to like.”