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Even fermentation is now being hampered by climate change

15 May 2024 By Kathleen Willcox

With climate change a daily concern in the vineyard, how are winegrowers reacting to its impact on the fermentation process as well? Kathleen Willcox investigates.

Gauging the real-life impacts of climate change is a tricky business—and sometimes, it doesn’t feel as extreme or even as negative as one might feel the hysteria laced headlines imply it should. Warmer winters in normally frigid Midwestern and Northeastern states, for example, might seem like the opposite of the end of the world.

But for anyone working in the wine industry, blissing out over 60-degree days in February is no longer an option. With climate change threatening to wipe out 90% of the world’s traditional winegrowing regions in decades, and billions of dollars in damage to harvests from wildfires, droughts and freak hailstorms in recent years, grappling with climate change in the vineyard and cellar is a daily, pressing, existential concern.

While much of the focus has been on adjusting farming methods to combat the effects of climate change, or offsetting energy expenditures in the cellar and via methods of transportation, increasingly, vintners are finding that even the seemingly simple, automatic process of fermentation is being hampered by climate change.

The process of fermentation

For millennia, winemakers have relied on yeast to transform grape juice into wine, and create the symphony of flavors, aromas and textures that makes it a $353.4 billion industry.

During fermentation, yeast converts the sugar in the grapes to alcohol. For millennia, the process of fermentation happened naturally. French chemist and microbiologist Louis Pasteur was the first person to study and document the process, and ever since, vintners and scientists have been working to perfect it. In the 1950s, commercial yeast products were developed and popularized.

While there are a number of commercially available yeast products on the market, many winemakers prefer to rely on the wild, indigenous yeasts that adhere to grapes in the vineyard, seeing spontaneous or wild fermentations as a more authentic way to reflect terroir.

“It is purely a philosophical choice as a winemaker,” says Bree Stock, winemaker at Artist Block Wine in Oregon’s Willamette Valley, and a Master of Wine. “Wild yeast fermentations provide me with the truest sense of capturing time and place in a wine. Commercial yeast inoculation tends to be chosen by larger more industrial commercial wineries that require consistency in their products, wines that are replicable year in and year out.”

Scientific studies back the long-held theory that microbial populations do vary considerably from place to place and year to year.

But climate change is threatening the health and viability of many of these populations, according to studies and winemakers who are witnessing the changes firsthand. Anecdotally, vintners are finding that wild yeast fermentations are changing, either more sluggish or increasingly speedy.

Changes in spontaneous fermentation

So-called spontaneous fermentation, for many, has felt anything but recently.

“It has been increasingly difficult to start spontaneous fermentations,” says António Sousa, winemaker and owner of 3 Rostos in Vinhos Verdes. “The proliferation and growth of indigenous yeasts in the grapes has been reduced and can often take more than a week to start.”

The slow start allows problem microorganisms like lactic and acetic bacteria to take control, Sousa says, which can “distort” the aromas and flavors of the wine.

Winemakers in other regions, like Texas Hill Country, are seeing the opposite.

“Our wild starts have actually become more frequent in the past several years,” says John Rivenburg, owner and winemaker at Kerrville Hills Winery in Kerrville, Texas. “We have obviously been a hot climate for a very long time, but we are seeing shorter seasons and big adjustment in harvest times.”

A fix: increasing time on-skin

Winemakers are finetuning fermentation techniques, often utilizing class red-wine making techniques on their whites, in a bid to streamline and stabilize spontaneous fermentations.

“The climate is making minimal intervention winemaking more challenging,” notes Stock, of Artist Block. “But by working with organic and biodynamic farmers, we find that yeast are still abundant. And we also find that on-skin fermentation helps ensure a more reliable fermentation process.”

In Stock’s exploration and experiments, she has discovered a number of benefits to extra skin time, in addition to speed.

“Many white grape varieties, Gruner Veltliner and Albarino, for instance, carry much of their flavor in their skins,” Stock says. “So by just taking their juice we are not working with the true expression of the grape, and not showcasing it’s authentic self. I also really like a little skin contact in white grapes that tend to be lower in acidity as the time on skins brings a light phenolic grip, which can have the perception of bringing acid and mineral structure to the wine.”

Rivenburg also finds that allowing whites with a little time on skin makes for smoother fermentation process, with multiple sensorial bonuses.

“Varieties like Picpoul Blanc and Sauvignon Blanc get better color absorption, and skin-tie also help build structure,” Rivenburg says.

But added skin time is not a panacea—nor is it suitable for all grape varieties.

“In varieties such as Alvarinho, Loureiro and Avesso, the short-time skin contact promotes the aromatic richness and volume in the mouth of the wine,” Sousa notes. “The only adverse factor is that the acidity of the must drops substantially, and the wine can lose its freshness. In our case, the Atlantic climate and richness of acids in our native grape varieties minimize this.”

Other grapes, like Azal and Arinto, do not perform well with skin contact, creating vegetal, bitter wines, Sousa says.

Making terroir-driven, balanced wine—especially today—is not for someone who thrives on predictability. Literally capturing time and place in a bottle requires vigilance, and constant attention.

“I don’t have a recipe for anything,” says Stock. “It’s simply a matter of being present each day, tasting and observing the arc of the fermentation as to when I decide to press of the skins.”

As the environment changes and extreme weather increases, it’s impossible to know where the impacts will be felt next. But it is clear that creativity fueled by data and analytics, and the ability to nimbly make adjustments on the fly will increasingly make all the difference between making wine and great wine.

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