It's not your imagination. Wine really has gotten boozier.

In the past two decades the maximum alcohol content of wine has crept up from about 13 percent to, in some cases, northward of 17 percent, a side effect of the growing popularity of wines with richer fruit flavor. The intoxication inflation has gotten so bad that wine scientists have begun to bioprospect for wild yeasts that turn a smaller quantity of the sugar in grape juice into alcohol during fermentation than does the yeast Saccharomyces cerevisiae—humanity’s partner in inebriation for thousands of years—but which can still produce a fine, finished wine.

A team of scientists from Australia and Spain now has apparently accomplished this enological first, having identified a new, wild yeast that reduced alcohol concentrations in Shiraz wine by 1.6 percent. The yeast may even improve or at least diversify the quality of the wines it helps make. Although many people enjoy stiffer wines, others are concerned by the effect of so much alcohol on these wines’ quality, not to mention imbibers’ health, and would welcome an option that provides the flavors associated with high-alcohol wines without the accompanying effects on blood–alcohol content.

The recent surge in wine's punch is largely a result, scientists say, of a fashion for deeply colored wines with fewer “green” qualities and more bright, ripe, fruity flavors. As New World wines in this style have drawn more fans, even European winemakers accustomed to making lower-alcohol wines in less ripe styles are beginning to follow suit. But producing wines with those flavors means letting grapes hang longer on the vine, and with longer hang times comes bigger sugar. The more sugar the wine yeast S. cerevisiae has to work with, the more alcohol it will make.

According to Matt Stamp, master sommelier and education director at the Guild of Sommeliers, the trend has its origins in wine expert Robert Parker's lauding of the 1982 Bordeaux vintage, but other critics and high-profile wine magazines have followed suit in giving high praise to full-bodied, concentrated, high-alcohol wines. “Those are the wines that are making 100-point scores,” he says.

More alcohol can also counterproductively dampen wine's characteristic bouquet. Most of the volatile components of wine—the chemicals responsible for the many fruity, herbaceous or earthy aromas—become more reluctant to diffuse from liquid to air in higher-alcohol wine. Stiffer wines may also incur higher taxes. And then, of course, there are alcohol's well-documented effects on waistlines, health and well-being. “You want to be able to have a glass of wine with lunch or dinner and be able to still function afterwards,” says James Kennedy, chair of the Department of Viticulture and Enology at California State University, Fresno, and president of the American Society for Enology and Viticulture, “and I think with these creeping alcohol concentrations people are concerned generally about ‘Are we drinking too much alcohol as a society?’ and ‘Should we perhaps try to tone it down a little bit?’”

Stamp agrees, and sees other problems. “Wines that are 15 percent alcohol and more are not exactly wines you can make it through two or three bottles of over the course of a meal with friends,” he says. “They're wines you might want to drink a glass of, but they're not wines that respond well to a lot of the more delicate styles of food we see in modern restaurants.” Sommeliers, he says, have begun pushing consumers to consider more moderate-alcohol wines with higher acidity and more delicate character that pair better with many foods, he says, and some have embraced the suggestions. But for those who prefer big, bold wines and would still like to be able to drive home, science may have a solution.

Finding ways to produce weaker dry wines from riper grapes has proved a challenge. Although there are more than 100 varieties of winemaking yeast—all S. cerevisiae—each of them produces virtually the same amount of alcohol given the same amount of sugar. Winemakers could stop fermentation early to reduce alcohol, but the unprocessed sugar would remain and make producing dry wine impossible.

Winemakers and scientists have already tried a variety of approaches to promote or preserve ripe flavors while reducing alcohol: clipping the leaves covering grape clusters, for instance, or changing irrigation practices or artificially removing alcohol from finished wine, all of which can affect flavor. The success of these strategies has been limited.

Alan Bakalinsky, associate professor of food science and technology at Oregon State University, who's long studied wine yeast, says that winemakers have tried to tinker with S. cerevisiae for years to get it to reduce it's alcohol production efficiency. But doing so can alter the yeast's winemaking abilities or cripple it, and certain methods of doing it may involve genetic modification that consumers may not like. Finding a wild yeast that already has the desired suite of traits would be a simple and elegant shortcut, he says.

So the Australian and Spanish team of scientists tried just this approach. “That was the motivation,” says Cristian Varela, senior research scientist at The Australian Wine Research Institute (AWRI) and a lead author on the study that sought new yeasts: “trying to find something simple that the winemakers could use easily in the winery.”*

This idea has been tried before, but no one had found a wild yeast that could lower alcohol without hurting quality. In the new attempt researchers began by creating a panel of 50 strains of wild yeasts from 40 species collected from grapes, samples from fermenting wines, fermented food or soil. They then subjected the panel to a battery of tests to see whether the wild yeasts could lower alcohol contents in finished wine. They inoculated standardized wine yeast chow with their experimental organisms and waited several days. They then added S. cerevisiae to finish the job, because wild yeasts can't consume all the sugar alone. Of the 50, only four strains produced less alcohol than S. cerevisiae alone did, and of those, one strain of Metschnikowia pulcherrima isolated from wine grapes produced the least, as the team reported online December 27 ahead of print in Applied and Environmental Microbiology. When they tested this yeast with real wine grapes and juice, it managed an alcohol drop of 0.9 percent in chardonnay and 1.6 percent in Shiraz, and the wine had chemical profiles consistent with good wine, they reported. “If you ask anyone in the industry a drop of this magnitude is very, very interesting for them,” Varela says. He has already been contacted by about 10 interested Australian winemakers and one from the U.S., although a yeast manufacturer would have to take charge of commercial production, a possibility he is exploring.

As a bonus, wine made this way might add interesting flavor complexity to wine. The dual-yeast wines had more “higher alcohols”—alcohol molecules that are larger and more structurally complex than ethanol (not the same as overall alcohol content)—than the control, but they were present in quantities that would be expected to enhance the olfactory complexity of the wine. The wine also had fewer “volatile acids,” which generally produce undesirable odors. The chardonnay had more esters, primarily two chemicals generally described as producing “pear” and “banana” flavors. But the chardonnay also had 6.5 times higher levels of ethyl acetate, a chemical said to convey “nail polish remover” at such concentrations. This level is unacceptable, but in the Shiraz the ethyl acetate concentration was low enough to add “desirable complexity.” “If you think of the thousands of winemakers in the United States, a lot of them want complexity in wine, it's an important part of it,” Kennedy, who was not involved in the research, says. “This in my mind appeals to that approach to winemaking: different yeast are going to create different compounds, and it adds to the complexity of wine potentially. And then if you have along with that the lower alcohol, that's a win–win.”

Work to develop the new yeast remains unfinished—particularly in understanding what conditions favor ethyl acetate production. Winemakers would be less skeptical of the new yeast, Bakalinsky says, if they could feel confident they knew how to avoid the production of such undesirable flavors. The scientists would also be well advised, Kennedy says, to figure out exactly where all the sugar not being converted into ethanol is going.

But so far, informal taste tests have been promising. In a small tasting at AWRI six of eight people who sampled the wine made with M. pulcherrima deemed it better than the control whereas two of the eight said the result was more or less the same. Varela's own impression of the Shiraz was that it was fruitier and more complex than the control wine.

It's also possible there's another strain of yeast of this or another species awaiting discovery that's even better at reducing alcohol without harming quality, because variation even within a given species of yeast seems to be considerable. Of the six strains of M. pulcherrima Varela and his colleagues tested only one was able to significantly reduce alcohol in both chardonnay and Shiraz wines. If this variability holds for other species, M. pulcherrima may be just the first of many new yeast tools available to winemakers interested in preventing their products from straying uncomfortably close to the realm of plastic jugs and flaming desserts.



*Correction (3/4/14): This paragraph was edited after posting to correct the spelling of Cristian Varela's name and his affiliation.



