CORTE FRANCA, Italy (AP) — Workers fan out before dawn to clip clusters of grapes destined to be transformed into Italy’s prized Franciacorta sparkling wine a full 10 days earlier than anticipated, as scorching temperatures brought the fruit to maturation earlier than ever.

Climate change is narrowing the window for harvesting wine grapes, forcing winemakers to make quick decisions when even a few days can mean the difference between a good vintage and a bad one.

“These are delicate, frantic moments, and everything has to work perfectly,” said Berlucchi CEO Arturo Ziliani, whose father, Franco, in 1961 became the first winemaker in the hilly Franciacorta wine-producing region to begin making sparkling wines with the “classic” method famously employed by France’s Champagne makers.

“We did not expect such an early harvest or such an acceleration in ripening,” Ziliani said.

Heat forces predawn picking under floodlights

Weeks of temperatures reaching highs between 37 and 38 degrees Celsius (99 to 100 degrees Fahrenheit), combined with below-average rainfall, have pushed some winemakers in Franciacorta to record the earliest start on record — about 10 days earlier than last year and about a month earlier than three decades ago.

Berlucchi, the oldest producer of Franciacorta, which is made using the traditional method of secondary fermentation in the bottle, began harvesting Aug. 2 as part of an industrywide effort to preserve grape quality in the face of increasingly extreme weather.

Experts say several factors combined to push Franciacorta’s harvest so early this year. A relatively mild winter meant the vines produced buds earlier, while hailstorms damaged some of the yield, lightening the fruit and bringing it to earlier maturation.

Even in late July, Berlucchi was targeting an Aug. 10 harvest date, but it quickly became clear that Pinot Nero used for sparkling blends and rosé was ready to be picked, signaled by rapidly rising sugar levels. Within two days, workers were mustered and the presses were readied.

The midday heat has been so extreme that workers are forced by regional labor rules to stop between 12:30 p.m. and 4 p.m., but winemakers say it has been too hot for the afternoon shift. To gain time and bring grapes to the presses before they are overheated, Berlucchi last week started the harvest at 4 a.m., with workers picking under the blaze of floodlights.

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

Sparkling wine requires complex calculations

It is not just Franciacorta that is starting early. Sicily began the wine harvest for still wines in late July. Small parts of Tuscany also started picking, as well as most sparkling wine regions.

The calculation is most complex for the makers of Champagne-style sparkling wines, which require a delicate balance of much higher fixed acidity, much lower pH and lower sugars than for still reds and whites.

“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 require the grapes to be cooled before being gently pressed in stainless steel machines to extract the highest quality free-run juice, a crucial step in sparkling wine production that cannot be rushed. Berlucchi operates up to 24 presses a day, often late into the night, to process the unusually early harvest.

Berlucchi remains Franciacorta’s largest producer, making about 4 million bottles annually, about 20% of the Franciacorta consortium’s total production of about 20 million bottles. About 90% are sold in Italy, with the remainder exported to markets including Germany, Switzerland, the United States and Japan.

Winemakers adapt to a new harvest calendar

“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.

With earlier harvests becoming a trend, winemakers say they will have to begin monitoring the fields even earlier to make sure they don’t miss the best harvesting moment.

“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.

Colleen Barry, The Associated Press