Climate change is impacting rainfall patterns, shifting vegetation boundaries, and leading to heat spikes and sunburn. Much of this can be managed with infrastructure improvements and additional work in the vineyard. However, what will be unavoidable is a sustained increase in temperatures—an effect that will affect traditional grape varieties. A glance at the alcohol levels of some famous wines today already reveals the significant, often undesirable, changes underway.
Varieties with star potential
Yet there are positive examples. After decades of being vinified as a white wine and valued for its acidity in Cava, the Trepat grape is now maturing as a full-bodied red with moderate alcohol and pleasant freshness in the DO Conca de Barberà. Similarly, in white wines, the French Picpoul de Pinet has evolved significantly. “When I was conducting research in Montpellier in the early ’90s, it was a simple, light wine. Today’s best examples are of an entirely different caliber,” explains Hans R. Schultz, who moved from southern France to Geisenheim University in 1995, where he is now president.
However, Picpoul also illustrates a research dilemma. Regional specialties receive little attention. “International relevance plays a role in selecting research subjects. On top of that, studying grape constituents and their drought and heat resistance are two entirely separate fields,” says Schultz. While some researchers look for vines that can withstand changing rainfall patterns, others focus on how aroma develops under various conditions, often using entirely different grape varieties.” In this field, there are significantly more projects with red varieties, as the effects are easier to measure in color compounds and tannins. With white varieties, the relevant compound groups often need to be identified first, which is much more challenging,” explains Schultz. Only by combining both areas of study can we identify the ideal vines for the second half of the 21st century, though collaborative initiatives are currently lacking.
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As head of the OIV’s climate group Schultz has a comprehensive view of global efforts in viticulture research. Montpellier's well-respected research institute also oversees the Domaine de Vassal, home to around 10,000 grape varieties and Vitis species. “The Domaine was nearly shut down due to high maintenance costs,” Schultz recalls, “but now its importance is widely recognized. Unfortunately, this awareness doesn’t come with a budget for systematic climate change research on these grape varieties.”
From Greece to France
Comprehensive research exists on about one hundred widely cultivated grape varieties. In 2008, Professor Cornelis van Leeuwen from the University of Bordeaux published a study on the heat requirements for bud break in key grape varieties. In the following years, Dr. Amber Parker expanded this knowledge with global data on ripening stages and sugar levels in grapes. “Global warming leads approximately to an acceleration of the various ripening stages, i.e. budbreak, flowering, colour change, softening or grape ripeness,” explains Parker, now director of the Centre for Viticulture and Oenology at Lincoln University in Christchurch, New Zealand. “There is a paradox with budding. Here, warming can also lead to a later start if the vine does not have a sufficient rest phase with low temperatures,' explains Parker. In general, however, all phases are brought forward. This often means that the development of flavours can be brought forward to a time that is still characterised by high temperatures. ‘This can have a negative effect on the flavour and the general quality of the wine,” says Parker.
In general, though, all stages are shifting earlier in the season, often meaning that aroma development occurs during intense heat. “This can negatively affect the flavor profile and overall wine quality,” Parker warns. Van Leeuwen gives specific examples: “All early-ripening varieties face challenges in their current regions, especially Chardonnay, Sauvignon Blanc, Pinot Noir, and Merlot.”
Publicly accessible research findings have already enabled practical applications, such as the successful introduction of Greece’s Assyrtiko grape in southern France. Its stable acidity and ripening period make it well-suited to the region. Mourvèdre also shows promise as a versatile candidate for wider cultivation.
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From obsolete to optimal
Another approach in the search for climate-resilient grapevines looks to the past, with projects in Portugal, Germany, and Spain rediscovering historical varieties. The logic is simple: what was once problematic might today be advantageous. Varieties like Catalonia’s Garró were previously dismissed due to excessive acidity or unreliable ripening in their native regions. Changing conditions, however, invite new assessments.
"Since we began over 40 years ago, we’ve rediscovered around 60 varieties, 14 of which have been approved, and we consider six of them particularly promising for viticulture, partly due to their heat resilience," explains Mireia Torres Maczassek, a fifth-generation member of the Torres family, who leads the company’s innovation efforts. “Since around 2000, we’ve been collaborating with the French agricultural research institute INRA and the Catalan INCAVI.” The process from discovery to market-readiness takes decades. Many ancient vines are infected with viruses and must be treated and propagated in vitro before planting material can be produced.
The outcomes are uncertain, but one rediscovered variety, the white grape Forcada, is currently showing great promise, offering high yields and exceptional quality even under challenging conditions. "We’ve already provided planting material to nurseries to encourage distribution. We rediscovered it, but it doesn’t belong to us," Torres remarks.
Mireia Torres wants to make data on old grape varieties available free of charge. (Photo: Familia Torres)
However, historical varieties have limited potential. Only a fraction have traits that are advantageous today; many were abandoned due to poor quality or low suitability for cultivation. And none will address the most pressing issue: “There isn’t a single classic Vitis vinifera variety that has even a hint of mildew resistance like PIWI varieties,” says Professor Dr. Kai Peter Voss-Fels, who has held the chair of plant breeding at Geisenheim for three years. Previously researching other crops, Voss-Fels enters the viticultural world free from entrenched debates around PIWIs. "Quality is the primary goal, but we also need sustainable production systems," he stresses.
The task extends beyond responding to climate change; it also involves addressing its root causes, including agriculture’s role. Reducing pesticides and their associated CO2 emissions requires resistant grape varieties. “Breeding works,” Voss-Fels insists, citing efforts to develop varieties with shorter growing cycles or Riesling clones that delay aroma formation to reduce the risk of petrol notes. Almost anything, he believes, is achievable.
"We must remember that there’s no Monsanto-equivalent in viticulture—no large agribusiness investing billions in grape variety development," Voss-Fels notes, emphasizing the need to set priorities. He is currently establishing a research network with colleagues in Germany and breeders from French institutes in Colmar, Montpellier, and Bordeaux. “Even the Champagne region is breeding PIWIs,” he explains. “These varieties show more positive and fewer negative characteristics, like the problematic foxiness, compared to previous generations. We’re gladly incorporating some of them into our own breeding efforts.”
Natural mutations
Between the initial cross-breeding and final approval, it often takes 25 years for a new grape variety to reach the market. Today, for example, Gelber Orleans is being cross-bred with PIWIs due to its very late ripening, yet strategies are needed to prepare for the next 30 years.
Besides breeding, clonal selection offers further possibilities. Plants naturally adapt to changing environmental conditions, and they also mutate randomly. “Everything is constantly mutating,” Voss-Fels explains, providing some numbers: “In a densely planted one-hectare vineyard, around one million random mutations occur annually.” Most of these have no significant effect and are undetectable. Yet Geisenheim has sequenced 250 Riesling clones, all genetically 100 % Riesling with a total of 1.1m mutations.
“Lower and higher must weights, bud break timing, and the balance of tartaric and malic acid are the key topics right now,” the plant breeding researcher elaborates. Geisenheim’s experimental facilities currently house 1,200 unreleased Riesling clones, and Voss-Fels aims to introduce the first of these to the market within the next decade. Parallel research on the genetic factors influencing ripening will provide further insights. He is optimistic: “We’ll develop breeds that enable Riesling cultivation well into the second half of the 21st century.”
There are positive signals from the breeding world, but the grape variety landscape will look different in 50 years. While identifying climate-adapted ‘winners’ remains largely anecdotal, initiatives to revive historical varieties are networking and sharing their findings freely. However, the potential of existing varieties has its limits, and new breeds with optimal growth and ripening characteristics will need consumer acceptance—a challenge the wine industry has historically struggled with.
