There are winegrowers who still remember harvesting in the snow. In 2022 the magazine Der Feinschmecker told the story of the Keller family in Rheinhessen, who in the 1960s picked Riesling with snow on the bunches. Today, in many places, harvest begins while it is still late summer outside. For hardly any other variety is this change as double-edged as it is for Riesling, which owes its reputation precisely to slow ripening in a cool climate.
Everything comes earlier
The most striking figures come from the Rheingau, where the weather has been recorded in Geisenheim since 1884. According to data from the Weinbauamt Eltville (the regional viticulture office) and the German Weather Service, circulated by the dpa news agency in 2015, Riesling there now buds around ten days earlier than 60 years ago. Flowering takes place some 15 days earlier than in 1955. Sugar accumulation no longer begins at the end of August but in early to mid-August. And the Riesling harvest starts at the end of September, three weeks earlier than in the 1950s.
The vine researcher Erika Maul of the Julius Kühn-Institut in Siebeldingen in the Pfalz has observed something similar: in 2020, bud swell in White Riesling began 20 days earlier than in 1982. That sounds like time gained, but there is a catch. The earlier a vine buds, the longer it remains exposed to late frosts.
More sugar, less acidity
Riesling lives on the interplay between fruit and acidity, and it is precisely this balance that is shifting. The Hessian State Office for Nature Conservation, Environment and Geology lists the composition of Riesling wine as an official climate-impact indicator, with series of measurements from the Eltviller Sonnenberg going back to 1971. Its finding is tersely put: since the 1990s the grapes have shown „weniger Gesamtsäure bei höherem Mostgewicht“ (our translation: “lower total acidity with higher must weight”).
The mechanism is well known. The climate portal of the state of Rhineland-Palatinate explains that in great heat alcohol rises and acidity falls, and that warm nights in particular accelerate the breakdown of acid. Because ripening now falls in the still-hot late summer rather than in cool October, the two come together.
Practice has adapted accordingly. For a long time the rule was: the more Oechsle (the German measure of must weight), the better. In 2021 the Rheinhessen winegrower Janine Brüssel summed it up: „Inzwischen ist der pH-Wert wichtiger als der Oechsle-Grad.“ (our translation: “These days the pH is more important than the Oechsle reading.”) Many estates now pick earlier and in several passes, to preserve freshness and keep alcohol levels in check.
Sunburn and thirst
Two further problems are more visible. The first is sunburn. The specialist portal Vitipendium documents a trial with Riesling in 2016 in which, at an air temperature of 34.8°C, up to 45°C was measured on the surface of the berries. According to the Julius Kühn-Institut, classic varieties such as Riesling suffered sunburn in the hot years from 2018 to 2020. The worst affected were vineyards that had been leaf-stripped shortly before the weather turned. The remedies are unspectacular: remove leaves early and only on the side facing away from the sun, so that the berries can harden off, or spray kaolin as a pale protective film. Classic canopy management, once intended to give Riesling more sun, is thus partly being reversed.
The second problem is water. In the assessment of the Rhineland-Palatinate climate portal, vines come under drought stress relatively quickly, and supplementary irrigation is becoming more important. A dpa report from Geisenheim cited 2015 as an example of such a dry summer and drew a comparison with 2003: when water and cool nights are lacking, Riesling loses its acidity and fruit. How far irrigation can help remains an open question. Speaking to WineSTR in 2023, the Württemberg winegrower Aaron Schwegler cautioned that, where water is scarce, viticulture cannot automatically take priority over the farming that feeds the population.
Geisenheim tests the future
How Riesling might taste in a few decades is being investigated by Hochschule Geisenheim in the open field. In the FACE2FACE project, the air above Riesling and Cabernet Sauvignon vines has been enriched with carbon dioxide since 2014 – according to a dpa report, to around 20 per cent above the level at the time. According to the university, this simulates the conditions expected around 2050. The question is whether growth, yield and quality change and whether pests increase. The first results, which the university presented in 2017, were more nuanced than feared: photosynthesis, biomass and yield per vine rose, sugar accumulation barely changed, and no quality-reducing differences had been found in the musts so far. Speaking to Der Feinschmecker, the Geisenheim professor of climate impact research Claudia Kammann was nonetheless blunt: Riesling was bred for a cool climate that, in parts of Germany, no longer exists even today.
The cool will win
For some regions, the change has so far been more blessing than burden. In 2021 Edgar Müller of the Dienstleistungszentrum Ländlicher Raum (the state agricultural service centre) in Bad Kreuznach recalled that on the Mosel, Riesling failed to ripen properly in 13 of the 23 vintages before 1987. With the warming since the 1990s, Müller said, this is no longer an issue. For the Saar, one of Germany’s coolest wine-growing areas, the wine writer Wolfgang Staudt estimates on his blog that ripe grapes could once be harvested there at most two or three times a decade, whereas today they can be in almost every year. He gives no precise figures, but others confirm the trend: Klaus Peter Keller told Der Feinschmecker that since the 1990s there has been no vintage that failed to ripen, and in 2023 two winegrowers from northern regions told WineSTR that fully ripe grapes were a rarity 30 to 50 years ago and are normal today.
Sites once considered second-rate are therefore in demand: higher elevations, parcels at the edge of the forest and slopes with a cooler aspect, right down to north-facing ones. In 2022 Der Feinschmecker described how warm riverside sites in the Rheingau are losing their appeal, while cool forest edges and higher sites are gaining. Further south the tone is more sceptical: Aaron Schwegler of Württemberg, mentioned above, intends to grow Riesling only for as long as the vines stay healthy and it makes sense under the prevailing climate.
And the north? The University of East Anglia has calculated that the area of England and Wales suitable for viticulture is likely to expand considerably by 2040. The study explicitly names Riesling among the varieties for which new suitable areas could open up. That is a possibility, not yet a movement.
Not a swan song
Riesling is not defenceless against climate change. It ripens slowly, as the Deutsches Weininstitut (German Wine Institute) emphasises, and is at home in cool sites. Such sites still exist in abundance on the steep slopes of the Mosel, Saar, Nahe and Rheingau. The style of the wines will shift, and so will the map of the vineyards. Perhaps in 30 years people will speak of the “great north-facing slopes” as they speak of the famous south-facing sites today. The snow on the grapes, on the other hand, nobody will miss.