What Determines How Much Alcohol Is in Wine?

So much of what we smell and taste in each sip of wine has to do with decisions made by the winemaker, like when they harvest grapes, how they treat them once harvested, and how and when they age their juice. However, the one thing winemakers appear to be losing control of is just how high the alcohol levels get in your wine. And that’s thanks to climate change. 

Alcohol, put as simply as possible, is created when the sugars in harvested grapes undergo fermentation. This means that the only way for winemakers to determine alcohol levels is to control the sugar levels in each grape by restricting how ripe the fruit gets. But, thanks to an increase in global drought and heat waves, that’s becoming increasingly difficult for producers to do. 

“The hotter the climate, the quicker the grapes become ripe and have a higher sugar content, leading to higher alcohol levels after fermentation,” says Thibault Dubreil, sommelier at Eli’s Table in New York City. “All over, we now see earlier harvests in an attempt to minimize [the effects of] global warming.”  

Charlie Gaeta, wine director of Dedalus, a natural wine shop in Burlington, Vermont, further adds that because the typical winegrowing season has had a “huge wrench thrown into it the past decade,” alcohol levels are more challenging to control. “Alcohol levels in regions that have been historically cooler or moderate are skyrocketing because of how warm it can get during the growing season,” Gaeta says. “I’ve had wines at 14-14.5% from regions that are traditionally 13%, that sweet spot for moderation in alcohol.”

But this story isn’t all bad news. Scientists and winemakers are working hand-in-hand (and even the U.S. government is in on the action) to ensure you can still enjoy your favorite glass for years to come. And, as Dubreil notes, there are a number of ways winemakers already know about to control the alcohol level in wine, including humidification, using wild yeast, using reverse osmosis, which involves putting the wine through a membrane to strip it of ethanol, or stopping fermentation with colder temperatures.  

In the case of stopping fermentation,  Luke Boland, wine director for the Hospitality Department which includes Point Seven and Press Club Grill in New York City, explains that it’s actually a “historic way of making wine in regions such as Port, Madeira, Jerez, and Marsala in which brandy (or a blend of brandy with a grape syrup) is added to the fermenting grape must in order to bump the alcohol to a degree which kills the yeast and stops the fermentation. The final wine can be dry or sweet and has a notably more punchy character from the increased alcohol content.”

There is one more way to combat this, and that’s through better planting practices in the first place. In a 2019 report published in the journal Agronomy, researchers concluded that yes, “vines are facing increasingly warm and dry growing conditions.” So, they suggested more drastic adaptations, including planting more “late-ripening and drought-resistant plant material,” aka varieties, clones, and rootstocks that can withstand the heat. “The vast genetic diversity in vines for these traits constitutes a precious resource to continue to produce high-quality wines with sustainable yields in a changing climate,” the report concluded. 

Still, as Boland noted, unless you’re specifically looking for a low-ABV option, you shouldn’t overthink it. “I wouldn't really factor in the alcohol by volume when considering the general quality of a wine,” Boland said. Instead, pick the one you like. And maybe consider upping your reduce, reuse, and recycle game while you’re at it.