How do winemakers combat heatwaves? - Ask Decanter

Carcassonne, France Credit: Unsplash / Boudewijn “Bo” Boer

Heatwaves in vineyards – What are the risks?

Winemakers need to know how to tackle unexpected heat, as shown by the recent heatwaves in France, but what are the risks to consider?

Loss of acidity

Most wines sit between around 3 and 4 on the pH scale.

‘Malic acid is quite sensitive to high temperature, and drops dramatically when temperature rises above 30° C,’ said Arturo Ziliani, CEO and winemaker at Berlucchi.

‘This acid is the main reason for Franciacorta freshness – otherwise we lose elegance and longevity, resulting in heavy, “jammy” wines.’

‘In order to fight heatwave, hand picking must be as quick as possible, to avoid acidity decreasing which may cause a loss in wine fresh character.’

Irene Mestre, winemaker at Colet Winery, in Penedès, Spain, says they try to keep the grapes shaded to keep them cool, but that ‘other winemakers might prefer to add tartric acid to the wine later, to help the acidity.’

Burning the grapes

Sokol Blosser Winery vines in the 40 degree heat. Credit: Sokol Blosser Winery Twitter

As well as the acidity levels, excessive sun and heat can burn the grapes, said Alex Sokol Blosser, winemaker at Sokol Blosser, in Oregon.

‘We could drop sunburned fruit, or spray on a sun block,’ said Sokol Blosser.

‘We make sure leaf plucking is restrained on western sides of vines especially to prevent sunburn,’ said Harry Peterson-Nedry, speaking to Decanter.com when he was winemaker at Chehalem Winery in the Willamette Valley.

In hot regions like Barossa Valley, vines are bush-trained to deliberately create shade for the grapes.

Protecting the style of wine

Elevation, such as here in Spring Mountain, provides cooler temperatures in hotter climates.

‘Loss of aromatic fragrance and loss of freshness is a risk in the heat,’ said Mestre.

‘It also depends on your style of winemaking – we focus more on what you can do in the vineyard, so we leave more leaves in the plant so that the grapes have more shade. We try to avoid adding much to the wines in the cellar.’

‘The finesse, elegance, higher acids and lower alcohols of our wines from the sensitive varieties like Pinot Noir we are known for, require continued attention to both climate and how we do viticulture and winemaking,’ said Peterson-Nedry.

‘Adaptations are required short-to-medium term to vineyards (siting of new vineyards to upper elevations, north-sides of hillsets, leaf plucking, irrigation, and croploads) to provide similar fruit to the winery; and adaptations to the winery processes (harvest timing, maceration steps, punchdown regimens, fermentation temperatures, additions).’

Working conditions

Red grape harvest at Kanaan Winery, Ningxia, China, Regional Trophy winner of 2015 DAWA. Credit: Kanaan Winery

It also slows up the vineyard work.

‘There’s also having to stop work in the vineyard after lunch because it is too hot,’ said Sokol.

With the current health warning in France, vineyard workers are starting shifts four hours earlier, to avoid working in the worst of the heat.

In particularly hot countries, some wineries choose to have the grapes picked at night.

A 2017 study published in the Temperature journal highlighted concerns around hot conditions for vineyard workers in Mediterranean countries. Researchers used time-motion analysis and found that extreme heat led to a significant loss of labour hours.

Originally published in 2017, and updated in 2019.

Translated by Leo / 孔祥鑫