© AFP

A combination of two yeasts provides an unprecedented reduction in alcohol levels.

There was a time not so long ago when 15 percent alcohol was reserved for fortified wines. A Bordeaux red that reached the 15-percent mark was inconceivable, yet in 2010, La Mission Haut-Brion hit 15.1, with its white wine trailing just behind at 15 percent. And the Graves estate is not alone in breaching previously unexplored territory.

A warming climate, improved viticultural techniques, efficient fermentation yeasts, and consumer demand for riper styles are all factors in the rise of higher alcohol levels. But the times are a-changin' as health-conscious consumers and lunchtime drinkers look for a lower-alcohol alternative to liver-bruising styles.

Researchers at the Australia Wine Research Institute (AWRI) point out that high-alcohol wines can not only leave your mouth burning; they can also compromise quality. While high alcohol might increase body and the perception of sweetness, “it can lead to a decrease in aroma and flavour intensity.” There’s also an economic concern: higher alcohol levels mean higher taxes.

As a result, wine producers have trying to make lower-alcohol wines by employing techniques in both the vineyard and winery. Picking early is one obvious way to reduce alcohol, but it is often at the expense of flavor ripeness. In the winery, technologies like spinning cone and reverse osmosis have been used as a method of alcohol removal, but many purists view this sort of intervention as the devil incarnate. Adding water to the tank in another option. While illegal in the European Union, it is not uncommon in warm New World countries – although getting anyone to admit to it is about as likely as Screaming Eagle throwing an open house.

Yeasts, the motor for fermentation, convert grape sugar into alcohol, and have been targeted as one of the most viable solutions to the thorny issue of high alcohol. However, research efforts to find a wine yeast to substantially reduce the final alcohol level in a wine have been nigh on fruitless thus far: the best attempts have managed to reduce ethanol by 0.2 to 0.7 percent.

Now, a study published by the American Society for Microbiology claims to have identified a yeast combination that can produce a significantly lower level of alcohol in wines and preserve the flavor.

While Sacchromyces cerevisiae is the main wine fermentation yeast, there are lots of other yeast species that can play a part at different stages of the process. Unfortunately, most non-Sacchromyces yeasts aren't able to consume all the sugar present in grape must, and often die at relatively low alcohol levels. But by starting a fermentation with a non-Sacchromyces yeast and then adding Sacchromyces partway through the ferment, this “sequential inoculation” technique appears to have worked.

© MicrobeWiki

Sacchromyces cerevisiae seen through a microscope

After many attempts, the scientists discovered that a non-Sacchromyces yeast with a name that sounds like a cross between Messerschmitt and Kalashnikov was just the ticket. Metschnikowia pulcherrima – also known as the easier-to-pronounce AWRI 1149 – was used to kick off the ferment before the S. cerevisiae was added halfway through. This combination reduced the alcohol content in shiraz from 15 percent to 13.4 percent, a decrease of 1.6 percent. The reduction in alcohol level in the chardonnay wine wasn't quite so impressive but still fell 0.9 percent.

"We don't know why chardonnay was less than shiraz," says the study's co-author Cristian Varela. "We haven't tried other varieties yet and that's something we'd like to do in the future."

On the downside, using AWRI 1149 caused an increase in acetate compounds in the chardonnay, which could add a nail varnish remover-like character to the wines. When it came to shiraz, Varela reports there were no negative effects on the smell or taste of the wine.

So what next for AWRI 1149? "We would like to work on a bigger scale with a couple of wineries to see if they can see the same results that we have seen – with the same drop in ethanol," says Varela. "Then, at the same time, trying to get yeast companies interested in the production and then commercialization of the strain."

While AWRI 1149 is being hailed as a breakthrough for wine producers grappling with high alcohols in a warm climate, these results have nothing on genetically modified yeast. The AWRI has already demonstrated that GM yeast can ensure much larger decreases in final alcohol levels. A GM yeast produced a reduction from 15.7 percent to 12.2 percent, though the use of genetically engineered agents is controversial. Varela explains that "most of the studies up to now were focused on Sacchromyces cerevisiae strains – mainly trying to do some genetic engineering, playing with genes to find a way to decrease alcohol. The main issue with those studies is that GMOs are not allowed in the industry."

Even so, a genetically modified wine yeast, ML01, which is able to carry out the malolactic fermentation at the same time as the alcoholic fermentation, has been approved in Canada. It produces fewer baddies that may cause headaches, but still attracts disapproval. A July 2013 Gallup poll found that 48 percent of respondents believed GM foods “pose a serious health hazard” – despite the fact that the scientific community and the World Health Organization have concluded there’s very little risk. Indeed, if you’ve eaten corn or soy of late, or used canola oil or sugar in your cooking, chances are you’ve consumed genetically modified food.

But with the industrialization of food and wine still creating a fear of the unknown, don’t expect GM yeast to come to the rescue of the high-alcohol issue any time soon. Until it does, we’ll have to go with the Metschnikowia pulcherrima.