Deciding picking dates for grapes in a changing climate

Unstable weather is making it increasingly hard to decide picking dates for grapes. We caught up with leading winemakers from Australia, France and the UK to find out how earlier harvests are impacting on grape quality.


Having always been at the mercy of Mother Nature, winemakers are acutely aware of the impact climate change is having on their livelihoods. Temperatures aren’t only rising, weather patterns are becoming increasingly erratic and extreme, and incidents of devastating wildfires, floods, droughts and late spring frosts are becoming more commonplace in the world’s leading wine-growing regions. In 2021, France was besieged by a cocktail of climate catastrophes, from destructive spring frosts and raging wildfires to violent hail storms. The April frosts across swathes of French vineyard land were particularly brutal, resulting in losses of up to EUR 2 billion.


Yields across France hit historic lows in 2021, down 30% on average, though losses were far worse in many areas. The Champagne region was heavily hit, bringing in its smallest harvest in 40 years –down by 60% –due to a combination of frost and mildew. Burgundy fared little better, with losses between 30-50%. 2022 brought new challenges, including a wild fire that swept through a pine forest in the Gironde, threatening historic vineyards in Bordeaux's Graves and Sauternes districts. Soaring summer temperatures and the resulting droughts have reduced yields across Europe, pushing harvest dates forward by a few weeks. In Jerez in southern Spain, the 2022 harvest began on 28 July; the earliest harvest in the region’s history.


Balancing act

Across the Atlantic, the UK recorded its hottest temperature on record on 19 July, when the mercury topped 40 degrees. Such statistics are alarming for winemakers, who rely on slow, even grape ripening to produce well balanced wines. A survival of the fittest scenario is starting to play out, and the winemakers that are the quickest to adapt to the changing climate, and have the means to invest in preventative measures, will be the most likely to weather the storm. Hotter temperatures are impacting on grape physiology, causing berries to ripen at a quicker rate and increasing their sugar content, leading to higher alcohol levels and cooked flavours. At the same time, acidity levels are decreasing, which is impacting on the freshness of the wines, while anthocyanins –which give red grapes their colour and protect vines from UV rays –break down under heat, which is negatively impacting on the tannic structure of the wines, especially if they’re harvested early to combat rising sugar levels.



Unstable weather is making it increasingly hard to decide picking dates for grapes.


If only sugar and acid were in play then growers could simply decide picking dates for grapes earlier to retain their freshness and keep alcohol levels in check, but if you pick too early then you risk under-developed tannins and anthocyanins, leaving vintners facing the dilemma of the optimum moment to pick in order to keep everything in balance. Many growers are picking earlier in order to retain the acidity within their grapes, though not at the expense of phenolic ripeness. It’s a delicate dance that’s becoming ever more challenging as temperatures continue their ascent. “Hotter maturation temperatures as the grapes go from veraison to sugar maturity impact on pH and the composition of acidity in the grapes. We’re seeing higher pH at picking and less malicacid,” says Tony Ingle, chief winemaker at Angove in South Australia, who reveals that picking dates at the estate have moved forward by around a month over the past half century.


Angove’s organic approach to winemaking is helping its vines to become more resilient to temperature changes, and the company has been planting in cooler areas of the country to future-proof itself. “If we’re going to stay in business for another 136 years then we have to give the market what it wants, and that means Chardonnay and Shiraz, so we’ve improved our vine irrigation systems and have changed our management of canopies, and also branched out into other regions like McLaren Vale and Tasmania,” says Ingle, who is also exploring the capabilities of hardier, more heat-tolerant varieties like Fiano and Carignan, which he’s planted at the estate. In the Barossa Valley, Yalumba’s chief winemaker, Louisa Rose, has found that spraying her less heat-tolerant grapes with a fine layer of white clay during summer heat spikes has been hugely beneficial in helping them to maintain their balance and freshness. “It’s quite revolutionary without being technical. The clay acts like sunscreen and stops tissue damage from excessive heat. It’s an effective way of maintaining the acidity in the grapes and slowing down the ripening process,” says Rose, who is currently trialling a number of different drought-tolerant rootstocks to help her vines perform better during prolonged periods of drought.


French revolution

In a bid to future-proof Bordeaux against the effects of climate change, last year the INAO allowed for the use of six new grape varieties in the region that are equipped to cope with high temperatures, including Marselan and Touriga Nacional. At Château Cheval Blanc, the use of year-round cover crops and the planting of over 3,000 trees is helping to protect the vines from scorching summer sun, while encouraging them to develop deeper root systems, helping them to retain water more efficiently in periods of drought. According to technical director Pierre-Olivier Clouet, Cheval Blanc’s shift to agroecology and earlier picking dates for grapes is helping to preserve the freshness, vibrancy and length of the estate’s grand vin, while maintaining the delicacy of its tannins. If the château hadn’t taken immediate action, Clouet believes the wines would be displaying higher alcohol levels, drier tannins and riper fruit –all of which he’s keen to avoid, as fine wines like Cheval Blanc hang their hat on tasting of their terroir.


While the effects of climate change have been devastating for many wine regions, for some of the world’s more marginal vine-growing areas, rising temperatures have been beneficial. “Forty years ago, we used to have to pick late into October and struggled to ripen our grapes, and now we can produce a vintage wine every year,” says Jean-Baptiste Lécaillon, cellar master at Louis Roederer. The picture isn’t entirely rosy, however, as Lécaillon admits that 2021 was the most challenging vintage of his 32-year career due to a hard-won battle against downy mildew. A champion of biodynamic viticulture, Lécaillon is exploring how Champagne’s lesser-known grape varieties, like Pinot Blanc and Petit Meslier, can be used in the fight against climate change via an experimental plot in the Marne Valley.


Expanding horizons

For Charlie Holland of leading English sparkling wine estate Gusbournein Kent, the recent run of warmer temperatures is opening up exciting opportunities in the still wine arena. “We’re keeping a close eye on the increasing potential for still wine production in the UK. We are now able to regularly ripen our grapes to a level that simply wasn’t possible 15 years ago, and high quality still wine production is something that Gusbourne has taken seriously for some time now. Future plantings are therefore likely to take this into consideration,” he says. Despite the scorching 40-degree temperatures in the south of England last summer, the 2022 harvest is shaping up nicely, with Holland predicting “an excellent vintage” similar in nature to the stellar 2018 crop.


“One of the main challenges we faced this year was a lack of rainfall, especially during the very hot periods. For more established vineyards with developed root systems this wasn’t so much of an issue, but young vines did start to show a bit of water stress,” reveals Holland, who has noticed picking dates creeping ever-earlier at the estate, though so far, this has proved advantageous. “We still have a relatively long growing season in the UK, so this isn’t yet having an adverse effect on grape maturity. In fact, picking in September brings many advantages –most notably that it’s generally much drier and warmer than October,” he says. When it comes to nailing the optimum picking date, Gusbourne’s FOSS analyser is coming in handy. “Having a FOSS analyser allows us to make well informed decisions quickly and accurately, which is important given that we have hundreds of different blocks that we want to pick, press and ferment separately. Given the complicated logistics of harvest, having greater visibility quickly and accurately is extremely advantageous,” he says.


Sizzling summer

Like Champagne and the UK, the cooler-climate region of Burgundy has yet to be severely impacted by climate change, but growers are aware of the need to tweak their vineyard practices in order to preserve the taste of their terroir. The start of the harvest at Drouhin, which owns vineyards in Chablis, the Côtes de Nuits and Côte de Beaune, has moved forward by a month in the last 40 years, but winemaker Véronique Drouhin has so far found this shift to be a good thing. “Up until now, global warming in Burgundy has been a benefit to the quality of the wines, and by extension to the pleasure of consumers. If you think back to the 60's and 70's there were more challenging vintages than good ones. Since 1985 we’ve been favoured with an extraordinary line-up of great years. Now we want the thermostat to stop going up, but sadly we know that won’t happen,” she says.


The last summer was a case in point – sizzling temperatures and drought conditions in Burgundy took their toll on vines that aren’t allowed to be irrigated under AOC rules. “We’re amazed at how resilient the vines have been after the heat and drought they went through. The older vines did a lot better than the younger ones. There were some dried berries, but the sorting tables are doing a good job removing them,” Drouhin says. Like Angove, taking an organic approach to viticulture is helping amid rising temperatures. “The vines are encouraged to fight against natural problems on their own and that includes the effects of climate change. We are, of course, concerned about rising alcohol levels, and canopy management is one way to tackle this issue, along with trellising and pruning,” reveals Drohuin, who hasn’t found that early picking has negatively impacted on the phenolic and physiological maturity of her grapes. “To get the picking dates right nothing beats the combination of walking through the vines tasting the berries and looking at the pips and behaviour of the plants, combined with berry samples to get an idea of the sugar and acids content,” she says.


While there is little winemakers can do about rising temperatures and increasingly erratic weather patterns, there are steps that can be taken in the vineyard to protect vulnerable vines against global warming, from picking earlier and clever canopy management to planting heat-resistant varieties and drought-tolerant rootstocks. A willingness to adapt is paramount if vintners want to preserve the taste of their terroir and retain the inherent character of their wines as the mercury continues to rise. It’s a fine balance that winemakers seem to be getting right at the moment, but only time will tell whether it’s a battle they will continue to win.