This article is more than 2 years old

This article is more than 2 years old

Climate change is putting one of the world’s oldest beer varieties at risk, environmental scientists and one of Belgium’s leading artisan brewers have said.

A study into temperatures in Brussels and the Pajottenland region south-west of the Belgian capital has raised doubts over the future of the sour lambic beer produced exclusively in the region.

Lambic is fermented in the open air through exposure to wild yeasts and airborne native bacteria. It relies on night-time temperatures of between -8C and 8C (18F-46F) for cooling and inoculation.

The traditional brewing season runs from October to April, with bezomerd – Brussels dialect for a beer that has had “too much summer” – a possibility if it is produced any later.

After cooling, the lambic is placed in wooden barrels where it is exposed to microbes living on the wood. The perfect temperature for ageing lambic is below 25C, above which the risk of unwelcome bacteria spoiling the beer rises.

A joint project between the climate scientists Mark and Asa Stone, Adam Harbaugh from the beer research site Lambic.info and the Brussels brewery Cantillon found this limited brewing window has shortened from 165 days in the early 1900s to about 140, as temperatures have pushed it later into the autumn and brought the season prematurely to an end in early spring.

It is feared the number of brewing days will shrink further, bringing the risk of a similar disaster to 2015, when beer had to be thrown away due to excessive temperatures.

Dr Mark Stone, a director at the University of New Mexico’s Resilience Institute, said: “The impacts of climate change are often gradual until a tipping point is crossed. Our results show that Cantillon is experiencing shifting brewing conditions, and that adaptation to avoid crossing a threshold will require changes in brewing operations that are outside of their traditional methods.

“The threat of climate change on traditional lambic production at Cantillon is indicative of the broader issue. That is, the impacts are not fully recognised until a threshold has been crossed, and adaptation strategies often exacerbate the problem while delaying the inevitable.”

Cantillon, which produces 400,000 bottles of the sour beer a year, has warned its ability to produce the beer could be under threat in the long term.

Jean Van Roy, Cantillon’s owner, told the Brussels Beer City blog that he believed if he artificially cooled the wort – a liquid extracted during the mashing process – it would change the taste of the beer.

“If tomorrow I would have this problem every season, financially it could be a bit difficult, so we would have to change something,” he said.

“[But] I would hate to do that … Or we move the brewery to go up north to begin to brew in Denmark, in Sweden, I don’t know.”