Workers spread out before dawn to clip grape clusters destined for Italy's prized Franciacorta sparkling wine a full 10 days earlier than anticipated, as scorching temperatures accelerated maturation beyond any precedent.

Climate change is narrowing the harvest window for wine grapes, forcing winemakers into rapid decision-making where a matter of days can determine whether a vintage is good or poor. Italy, consistently ranked among the world's top two wine producers by volume alongside France, faces particularly high stakes as shifting weather patterns disrupt centuries-old viticultural rhythms across its diverse wine regions.

"These are delicate, frantic moments, and everything has to work perfectly," said Berlucchi CEO Arturo Ziliani. His father, Franco, alongside estate owner Guido Berlucchi, pioneered sparkling wine production in the northern Italian region of Franciacorta — a DOCG-designated area in Lombardy and one of Italy's most prestigious appellations — using the "classic" method famously associated with France's Champagne makers.

"We did not expect such an early harvest or such an acceleration in ripening," Ziliani added.

Weeks of temperatures peaking between 37 and 38 degrees Celsius (99 to 100 degrees Fahrenheit), paired with below-average rainfall, have driven some Franciacorta winemakers to their earliest harvest start on record — 10 days earlier than last year and roughly a month earlier than three decades ago. The shift reflects a broader trend documented across European wine regions, where harvest dates have moved progressively earlier over the past two decades as average temperatures have risen.

Berlucchi, the oldest producer of Franciacorta — which relies on the traditional method of secondary fermentation in the bottle — began harvesting on Aug. 2 as part of an industrywide push to safeguard grape quality amid increasingly extreme weather.

Experts attribute the unusually early harvest to a combination of factors. A relatively mild winter caused vines to bud earlier, while hailstorms damaged a portion of the yield, lightening the fruit and hastening maturation.

Even in late July, Berlucchi had been targeting an Aug. 10 start date. It soon became clear, however, that Pinot Nero used for sparkling blends and rosé was already ready for picking, signaled by rapidly rising sugar levels. Within two days, workers were assembled and presses prepared.

The midday heat has grown so intense that regional labor rules mandate a stoppage between 12:30 p.m. and 4 p.m., but winemakers report it has been too hot for the afternoon shift regardless. To maximize picking time and get grapes to the presses before they overheat, Berlucchi last week shifted its harvest start to 4 a.m., with workers picking under floodlights.

"The grapes are perfectly healthy," said Ferdinando Dell'aquila, an oenologist and Berlucchi's technical director. "We just have to work as quickly as possible, harvest them and preserve their acidity."

Franciacorta is not alone in its early start. Sicily began harvesting still wines in late July. Small areas of Tuscany also commenced picking, along with most sparkling wine regions.

The challenge is greatest for producers of Champagne-style sparkling wines, which demand a delicate balance of higher fixed acidity, lower pH, and lower sugars than still reds and whites require.

"Early-ripening varieties such as Chardonnay require great care, because a delay of just a couple of days can leave you with grapes unsuitable for sparkling wine. Sugar rises too quickly and acidity falls too quickly," said Attilio Scienza, a professor emeritus at the University of Milan.

High outdoor temperatures mean grapes must be cooled before being gently pressed in stainless steel machines to extract the highest-quality free-run juice — a critical step in sparkling wine production that cannot be rushed. Berlucchi runs up to 24 presses a day, frequently operating late into the night to handle the unusually early harvest.

Berlucchi remains Franciacorta's largest producer, turning out approximately 4 million bottles annually, representing about 20% of the Franciacorta consortium's total output of roughly 20 million bottles. About 90% of its production is sold in Italy, with the remainder exported to markets including Germany, Switzerland, the United States, and Japan.

"Climate change and the African weather systems settling over Europe are bringing extraordinary temperatures and forcing early picking, not only in Italy, but also in France and Germany," said Paolo Castelletti, secretary general of the Italian Wine Union trade organization.

As earlier harvests become a trend, winemakers say they will need to begin monitoring vineyards even sooner to avoid missing the optimal picking moment. Researchers studying European viticulture have warned that traditional grape varieties in some southern growing zones may eventually become unsustainable if temperature trends continue, raising longer-term questions about which cultivars can adapt and which regions may need to transition.

"A good oenologist can manage situations like this. I can say with confidence that wine quality is not compromised. It simply requires a different organization of work than in past years," Castelletti said.

This story was originally featured on Fortune.com.