The Impact of Climate Change on Viticulture and Winemaking and PIWI Varieties as a Future Alternative
Nana Jojishvili | IWI Sommelier
Addressing the challenges posed by climate change has become a pressing issue on the global agenda. Rising temperatures are affecting every continent, impacting agricultural sectors worldwide, including viticulture and winemaking. To discuss solutions and explore alternatives in this field, industry specialists gathered in Berlin in early November for the first PIWI World Summit 2025, which I also attended.
PIWI International is a global organisation that supports grape varieties resistant to fungal diseases. The initiative to establish the group came from Swiss viticulturist Pierre Basler in 1999. The PIWI logo was created in 2004, and in 2015 PIWI International was registered as a trademark. The organisation’s main goal is to share both scientific and practical knowledge about PIWI varieties.
‘PIWI International brings together more than a thousand wineries from 31 countries around the world. Each member country with its own PIWI association is a part of our international group, while in countries where such associations have not yet been established, individual wineries can join PIWI International directly. This year, the summit aimed, on one hand, to connect viticulturists, winemakers, scientists, grape nurseries, and vine breeders from different countries to share their knowledge and information. On the other hand, through tastings held at the summit, it sought to showcase the quality of wines produced from PIWI varieties to the Berlin audience,’ says Christian Waltl, the General Manager of PIWI International. At the 2025 summit, wines from 32 producers across six countries – Italy, Austria, Germany, Spain, Slovakia, and the Czech Republic – were presented.
PIWI (Pilzwiderstandsfähig) refers to grape varieties that are resistant to fungal diseases and naturally robust in challenging climatic conditions. Their development began in the nineteenth century, when fungal diseases brought from America to France caused severe damage to European viticulture and prompted efforts to breed more resilient varieties.
It was at this point that breeders began crossing European vinifera vines with non-vinifera American hybrids, using pollination and selective breeding to develop PIWI varieties capable of resisting fungal diseases. The grape varieties used in traditional winemaking belong to the Vitis vinifera group. They are generally more susceptible to fungal diseases than American hybrid vine species. Breeding new grape varieties from these two groups aimed to bring together their best qualities into a single vine that would be resistant to disease, frost, and high temperatures, while still capable of producing quality wine.
David Chichua | LEPL Scientific-Research Center of Agriculture, Professor |: Hybrid grape varieties are created by crossing cultivated Vitis vinifera sativa with American species such as Vitis labrusca, or with the Asian species, Vitis amurensis. However, it is important to distinguish between the so-called direct-producing hybrid vines used 150 to 100 years ago for their resistance to downy mildew, powdery mildew, and phylloxera, and the new generation of PIWI varieties developed through selective breeding over the past 30 years. In addition to their disease resistance, first-generation hybrids are characterised by higher pectin content in the pulp, which leads to significant sediment formation in wine and an increased production of toxic methanol during fermentation. In addition, the wine’s aroma is dominated by furaneol and methyl anthranilate, giving wines from these varieties a distinctive ‘hybrid’ character, which, while it’s young, can evoke a scent reminiscent of wild strawberries.
In most cases, the pulp of older hybrids is deeply pigmented, and their wines appear much darker than Saperavi when they’re still young. However, as they age, the colour almost completely settles, leaving the wine with a yellowish-copper hue. As for the new generation of so-called PIWI varieties, the influence of American species on their genetics, morphology, and oenological characteristics is minimal, showing up almost exclusively in their resistance to diseases. European regulations permit their use in winemaking.
Mr.Chichua, what is Malvidin-3-glucoside and what effect does it have in wine?
Malvidin-3-glucoside is the primary colouring compound in European grape varieties, whereas in American hybrids, over 60% of the red pigment consists of malvidin diglucosides. The latter are not found in European grape varieties, which is why this compound serves as a ‘marker’ for American hybrids. A malvidin diglucoside content of more than 15 mg/L in wine indicates that the winemaker has deliberately intensified or darkened the wine with American hybrids, which is against the law. Interestingly, malvidin diglucoside does not form stable pigment complexes with tannins during ageing, which explains why wines made from hybrids lose their colour over time.
Wines from PIWI Varieties as a Model of Eco-Sustainable Production
Wines from PIWI grape varieties were first made in France around 150 years ago. Their use was long prohibited in European wineries. Due to problems arising from global climate change that directly affected various agricultural sectors, including viticulture and winemaking, work on PIWI varieties resumed in Europe from the 1970s. Since then, the topic of PIWI varieties has become even more relevant.
Among fungal diseases, powdery mildew (Latin: Oidium) is particularly widespread. It appears as a white coating on the upper surfaces of leaves and on the grape berries. The disease can cause berries to split and increases the risk of a lower-quality harvest. During this period, vineyards are treated with a sulphur-based solution.
Downy mildew (Latin: Peronospora) is another widespread fungal disease, affecting the underside of grapevine leaves. It appears as yellowish, bluish, or greyish patches. At this stage, photosynthesis in the plant is disrupted, and the flow of sugars to the berries is impaired. As a result, the wine produced is thin, pale, and of lower quality. The plants are treated with copper-based preparations.
In addition to the solutions mentioned above, many vine growers often spray vineyards with stronger chemical preparations, which, while effective against fungal diseases, also harm the ecosystem. In contrast, in organic, biodynamic, and natural vineyards, the use of such treatments is strictly controlled and permitted only in limited quantities.
Winemakers’ interest in PIWI varieties has been driven by growing demand for biologically clean, natural products, including popular examples such as natural amber wines and pét-nats. PIWI varieties are particularly resilient to fungal diseases. Vineyards planted with these varieties require far fewer treatments than those with Vitis vinifera varieties, reducing the need for chemical preparations by around 75%.
Wines produced from PIWI varieties are considered eco-sustainably made and are often referred to as eco-friendly wines. Today, sustainable production is one of the most relevant terms, adopted not only by wineries but by producers of all sizes across various industries.
The Impact of Climate Change on Grape Varieties
In 2024, the highest average temperature was recorded globally. Since 1850, the global average temperature has risen by approximately 2.47°C. This change has affected plant physiology, vineyard agronomy, and the oenological characteristics of the fruit. Rising air temperatures, changes in precipitation patterns, and increased atmospheric carbon dioxide have disrupted the centuries-old rhythm of vine growth.
The timing of grape ripening has shifted, the sugar levels in the berries have changed, and the balance between acidity and sugar, which determines the wine’s organoleptic characteristics, has been disrupted.
As a result of climate change, vines experience water stress, but PIWI varieties are highly resistant in this regard.
Germany is generally considered a cooler region compared to neighbouring wine regions, such as France and Italy. This year’s summer, however, was particularly hot in the Rheingau. In mid-June, we visited Riesling vineyards on the famous terraces in Rüdesheim, managed by Geisenheim University. At this time, the vines were under stress from the high temperatures. For many winemakers, a drip‑irrigation system is considered a luxury, and in Germany it also involves substantial bureaucratic procedures.
Riesling is Germany’s leading white grape variety, known for its vibrant acidity. With temperatures on the rise, questions are increasingly being asked: how will climate change impact this variety, will it alter its core organoleptic characteristics, and what solutions or alternatives are available?
According to Geisenheim University professor Manfred Stoll, ‘It is hard to imagine a region with a centuries-old tradition of producing wine from Riesling having to say goodbye to this variety. Replacing it entirely with another grape would also be difficult. In the Rheingau, there are several wineries with long-standing Riesling traditions, such as Schloss Johannisberg and Schloss Vollrads.
Fortunately, today PIWI varieties can be found in a small number of German wineries, including Germany’s first red PIWI grape, Regent, which currently covers just 2,500 hectares. In Germany, in terms of vineyard area, these varieties only occupy a very small portion. Interestingly, demand for German PIWI varieties is high in neighbouring countries, and a significant portion is exported to Italy and France.
The cultivation of these varieties is officially permitted in Germany. Under German wine law, each Bundesland (federal state) determines which PIWI grape varieties are allowed in its region, which in turn helps to strengthen these varieties and raise their profile.’
Today, the most widely planted PIWI variety in Europe is Cabernet Blanc, followed by Souvignier Gris, Solaris, Muscaris, and Johanniter. Among red varieties, the most common are Regent, Pinotin, Cabernet Cortis, Prior, and Satin Noir.
Climate change has posed challenges for winemakers in old wine countries. At the same time, new wine countries have emerged on the global map, particularly in northern Europe, where, just half a century ago, the climate was considered unsuitable for wine production. Examples include Denmark, Norway, and England. One of the best wines I have tasted made from a PIWI variety comes from a Danish winery: Solaris, priced at €34.
The Resilience of Georgian Grape Varieties to Climate Change
Under Georgia’s Law on Vine and Wine, the use of PIWI varieties is prohibited. Producers are only permitted to use cultivated Vitis vinifera varieties. In the 1990s, hybrid grape varieties spread across Georgian vineyards: Adesa/Isabela in Guria, Vakirula in Kakheti, and Dirbula in Kartli. This expansion was largely a result of disruptions in the country’s viticulture and winemaking sector at the time. Over the past 15 years, these areas have been gradually replanted with Georgian cultivated varieties.
Today, PIWI grape varieties cannot be found in Georgia. This issue is effectively closed, partly due to the intensive spread of the three hybrid varieties mentioned above, which threatened the popularisation of Georgia’s endemic grape varieties.
The diverse gene pool of Georgian grape varieties is distributed across the country according to regions and terroirs, which more or less allows for disease management in the vineyards. However, ongoing climate change worldwide is also creating challenges for Georgian vine growers.
Giorgi Samanishvili | Master in Oenology |: I should point out that Georgia is indeed behind when it comes to resistant grape varieties, and the law plays a secondary role here. The law prohibits the commercial cultivation of non-European varieties or hybrids but allows them for experimental or personal use. This means that any interested researcher can plant these varieties on a smaller or larger scale for testing.
The issue is that, under the climatic conditions of our regions, research on foreign resistant varieties is virtually non-existent. More importantly, we are not working on crossing Georgia’s traditional, exceptionally high-quality varieties with other resistant forms to develop Georgian resistant, or so-called PIWI, varieties.
We all understand that, in the coming decades, global climate change and stricter restrictions on pesticides will make it increasingly difficult to preserve traditional varieties. If we do not begin work today on identifying and developing alternative varieties, we may have to say goodbye to our prized grapes and replace them with PIWI varieties from other regions, which is certainly not a viable solution.
I believe we need to start work on new varieties without delay. If interesting forms emerge during research, we can also test them on relatively larger areas. The law does not restrict this, and if any obstacles arise, changing the legislation is not difficult, especially when pursuing such important objectives.
I would like to stress once again that developing new forms from Georgian varieties is, in my view, the greatest challenge. I do not support the introduction and spread of foreign PIWI varieties in Georgian winemaking without first conducting research.
Regarding the drought resistance of Georgian grape varieties, a study conducted by Tekle Zakalashvili, Head of the Ministry of Agriculture’s Research Centre for Plant Micro-clonal Propagation and Virus-free Planting Material and doctor in viticulture and vine breeding at the Agricultural University of Georgia, found that the traditional Georgian grape variety Mgaloblishvili shows strong resilience to drought.
Her research was inspired by a study conducted by Italian scientist, Silvia Laura Toffolatti. For the same study, Toffolatti selected Mgaloblishvili alongside PIWI varieties. The research showed that in terms of drought resistance, Mgaloblishvili is on par with the aforementioned PIWI varieties.
‘As we know, the vine rootstock determines drought tolerance. As for sunburn and overall resistance to water stress, my research showed interesting results in varieties such as Mgaloblishvili, Rkatsiteli and Tsolikouri. Under Georgia’s Law on Vine and Wine, wine must be produced from Vitis vinifera, i.e. cultivated grape varieties. Since PIWI varieties contain American or other non-European genetic material, they are not currently used in commercial production in Georgia. On the other hand, studying the genetic diversity of Georgian grape varieties allows us to identify relatively resistant, disease-tolerant vines within the traditional Vitis vinifera cultivars. Research by Silvia Laura Toffolatti shows that Mgaloblishvili possesses unique resistance due to specific loci (regions of a chromosome where particular genes are located). Studies on this variety have also been carried out at the University of Davis in California and the University of Milan,’ says Tekle Zakalashvili.
Advantages and Challenges of PIWI Varieties
In both economic and ecological terms, PIWI varieties offer clear advantages: they require fewer treatments, helping to maintain biodiversity in the vineyard and allowing winemakers to offer a more natural product; reduced machinery use minimises soil disruption and lowers CO2 emissions; and disease resistance lowers the risks and costs associated with harvesting.
‘In the future, I plan to convert my vineyard, which covers 16 hectares, entirely to PIWI varieties, depending on interest and demand from both the HoReCa sector and retail. As for replacing traditional grape varieties with PIWI vines, this is a process driven by climate change. As in other fields, winemaking must remain open to innovation and change, especially when these changes benefit nature and the environment.
As you may know, by 2030 the use of plant protection products in vineyards will be reduced by 50%, making wine production with traditional grape varieties more challenging, particularly for organic wineries. By replacing traditional varieties with PIWI vines, I will make the path easier for my children in the future,’ says Austrian winemaker Harald Lieleg of Kollerhof winery.
Among the speakers at the PIWI World Summit 2025 were wine market experts who believe that wines made from PIWI varieties could easily capture 20 to 30% of the European market. Most white PIWI varieties are characterised by high acidity. To balance this, winemakers have used various techniques, including ageing on the lees or in barrels, and it is worth noting that these methods proved quite effective, also influencing the price: wines aged in stainless steel sold for an average of 8 euros, while those aged on the lees or in barrels for 12 months or more fetched around 13 euros.
During the summit, I tasted wines starting at 19 euros. It was particularly interesting to try sparkling wines made from PIWI varieties. Thanks to their naturally high acidity, these grapes are considered a good alternative for sparkling wine production.
Another interesting finding was that some of the smaller wineries at the summit have vineyards planted entirely with PIWI varieties, while in medium-sized estates (around 10 to 15 hectares), PIWI varieties account for roughly 20 to 25% of the vineyard area.
At the summit, the main message from wine market specialists to winemakers was the importance of proper communication with consumers and selecting the right marketing strategy. The two-day event in Berlin highlighted that, until the world reaches an agreement on addressing the 21st century’s major challenge – managing climate change – PIWI varieties remain an alternative for the future.
