On a sunny, warm day in November 2021, Kaan Kurtural, a viticulture researcher at UC Davis, leads us to a plot of vines at the Oakville Experimental Vineyard in Napa Valley, nestled between nearby forest-covered hills other commercial vineyards. Since 2016, Kurtural and his colleagues have been monitoring 16 unique combinations of Cabernet Sauvignon rootstocks and clones to learn which combinations are most resilient under stressful conditions like heat waves and drought while producing Cabernet Sauvignon grapes of high quality.
Some of the experimental grafts – including one with a French rootstock called 420A – look clearly withered and, after just five years, some of them are dead. But others – including those grafted on Austrian Kober 5 BB rootstock, French 3309 Couderc and 110 Richter – seem more vigorous and leafy.
Andy Beckstoffer, a prominent Napa winemaker who is working with Kurtural on a similar trial at one of his own vineyards, tells us he thinks the results will be a boon for Cabernet Sauvignon in years to come. “I hope we find new combinations that tackle climate change and also improve wine quality,” he says.
Growers around the world are already modifying traditional practices to mitigate the effects of global warming. Grapes are often harvested earlier in the year to avoid over-ripening and, in fire-prone regions, to miss the worst of wildfire season and avoid the smell of smoke. Bordeaux workers now rush to pick the berries early in the morning when the acidity is highest, and they prune the bushy plants to curb sugar production.
At the Oakville Research Station, Kurtural shows us experiment after experiment studying the effects of different viticultural practices, including a carbon-sucking grass that can grow between rows and vines tied to wires in many trellis styles. . Fortunately for places like drought-stricken California, the solution isn’t just more water; his research suggests that the most balanced and aromatic wines come from vines subjected to constant and mild water stress. Tackling solar radiation might be a better way forward.
“Certain regions of the spectrum can be damaging, like near-infrared light,” he explained earlier — they heat up the plant and the berries. At the vineyard, he leads us to a plot of Cabernet Sauvignon vines that have spent the last two seasons under umbrella-shaped shade films. The films slow the ripening process and do not seem to affect the number of berries produced by the vines.
We taste the difference during the same trip, at a viticultural research conference at UC Davis. There, Lauren Marigliano, one of Kurtural’s graduate students, presents a chemical analysis of grapes fully exposed to the sun or protected by different types of shade. Thereafter, she provides wine samples of three treatments for the audience of researchers, winemakers, and winemakers to try.
Around us, professionals shake their glasses, sniff, take sips and then spit into small plastic buckets. We watch their technique and follow suit carefully. The first wine is quite bitter, and the second has a less complex taste – a close expert unfortunately declares it “square”. We like the third one, which has a bolder berry aroma and a sweeter taste. Attendees murmur approvingly at its “roundness.”
It turns out that this “round” came from grapes grown under a shade film that blocked about 30% of near-infrared light, the wavelengths most responsible for heat transmission. By cooling the grapes, the film allowed them to accumulate higher concentrations of heat-sensitive anthocyanins than the grapes for the first and second samples. One was grown with a less effective shading film that blocked a different set of wavelengths, the other without any film. The winning film still lets in enough light for sun-dependent compounds to build up, creating a fuller-bodied, full-bodied red wine, Marigliano tells the audience.
But it is not always economical for farmers to erect long films along their vine rows, especially over large areas. This is where the trellis comes in. During our tour of the experimental vineyard, Kurtural stops at one point to gesture toward a row of vines winding along a single hanging wire. This style of trellising works similarly to good shade film by allowing the vine leaves to shade the fruit, he explains.
Practices such as shade films and grape protection mesh were mostly restricted to Australia, South America, Israel and Spain. “Now, with climate change, there’s 30 years of good research on warm climate viticulture that is suddenly relevant to places like Burgundy, Beaujolais, Germany, Napa and Sonoma,” says Steve Matthiasson , a Napa Valley wine producer who embraced shade cloth. He also planted his vines in a northeast-southwest orientation so that the sun shines directly on the vines, leaving the fruit protected by the leaves.
“Napa,” he marvels, “was a cool-climate growing region a generation ago.”
Repairing climate impacts in wine
Even the toughest grapes can’t always withstand extreme heat and smoke. So researchers and wine producers are also developing ways to work with crops affected by climate while producing well-balanced wines.
Oberholster believes that many of the vines left unharvested after the massive California fires in 2020 could still have produced good wine, so she encourages producers to do it on a small scale”bucket fermentations“a few weeks before harvest to test the smell of smoke – since fermentation releases these ashtray-tasting phenols. Producers can then send a sample of wine to a lab for analysis and taste the micro-lots themselves – they could detect changes that a commercial lab would make miss, since labs only select a limited menu of compounds and could declare a wine good when it’s not.
It can also help, adds Oberholster, to sweeten smoky wine with a little grape concentrate — that way the extra sugar stops the enzymes in your mouth from releasing phenols. Even better would be to completely eliminate phenols, but current treatments, which include activated carbon and reverse osmosis, target a broad class of smoke compounds. So – inevitably – they also take away some desirable aromas. To that end, Oberholster is looking at enzymes used in the food and beverage industries to find those that might help break down unwanted compounds in wine and make them easier to filter.
Wine blending techniques can also help. Beckstoffer, for example, says his 2020 smoked grapes have been fermented and, when mixed with uncontaminated wines, “can’t fit in a $200 (£165) bottle of wine, but a lot of them could go in a $40 (£33) bottle of wine.”
And Matthiasson carefully mixes the varieties to balance the flavors: he picks the Cabernet Sauvignon early in the season to preserve acidity, but it also means the grapes have less tongue-choking or mid-palate richness. It therefore mixes Petit Verdot grapes to swell the mid-palate and Cabernet Franc to fill in the lack of herbaceous aromas.
He also planted an emergency reserve of the Sagrantino variety — “for 20 years on the road” — which is rich in tannins that Cabernet Sauvignon grapes lose during warmer nights.
Warmer temperatures are threatening Matthiasson’s preferred style: wines with less alcohol and more acidity than most full-bodied wines popular today. But he doesn’t think raisin wine everywhere is inevitable. In fact, some studies suggest that much of the increase in stronger, sweeter wines is a choice driven by winemakers and consumer demand, not just because of global warming. “I’m very frustrated with winemakers who use climate change as an excuse for overripe, rich, jammy wine when it isn’t,” he says.
Viticulture is also moving to high technology to adapt to climate change. In France, microbiologist Fabienne Remize from the University of Montpellier has developed new strains of yeast that produce less alcohol during fermentation, to circumvent the problem of excess sugar. Scientists have also developed an electrodialysis process that can increase the acidity of wine by removing ions such as potassium; the method has been adopted by winegrowers in France, Morocco and Spain.
The future of wine
The bigger question for climate wine and the adaptations proposed by researchers and wine producers is, of course: will people continue to buy it and enjoy it?
One of the most surprising lessons from consumer research is this adoption of bolder, more jammy wines, as noted by Kurtural and Gambetta. In a study of Napa and Bordeaux red wines, they found that wine ratings have actually increased over the past 60 years, even as these regions have warmed. The results, they wrote, appear to negate an earlier prediction that quality would peak at an average growing season temperature of 17.3 C (63.1 F) – which both regions have long since passed.
Yet Kurtural and Gambetta also note that we could reach a tipping point where warmer temperatures wear down secondary compounds beyond growers’ ability to adapt. “Frankly, we don’t know what the optimum is,” says Gambetta. “We need better tools and better analysis to know how far is too far.”
Matthiasson, for his part, believes that great wines will resist global warming. With his shade cloths, blending techniques and emergency Sagrantino stash, he’s ready for what’s next. “I think we will be able to adapt,” he said. “In the short term, our rate of learning is faster than the rate of climate change.”
* This article originally appeared in Knowable Magazine, and is republished under a Creative Commons license.
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