Call it the modern winemaker's dilemma—better vineyard techniques and a warming climate in many regions have made it much easier to ripen grapes. The flip side is that picking fully mature fruit often means high sugar levels, which lead to wines with higher alcohol levels. If the wine tastes balanced, no problem, say many winemakers. But what if it doesn't?
A team of researchers at the Australian Wine Research Institute have a potential answer: They have isolated a strain of yeast that, in lab tests, has produced lower-alcohol wines. During trials, an Aussie Shiraz was made with alcohol levels 1.4 percent lower than a conventionally produced wine from the same must. In a test with Chardonnay, alcohol was 0.9 percent less.
Alcohol levels tend to ignite heated discussions among wine lovers—some claim high alcohol means unbalanced wine while others say it depends on the wine. But there are some practical considerations. For one, wine over a certain alcohol level is often taxed at a higher rate. More commonly, winemakers want to reduce alcohol levels in some wines because they feel it impacts the taste.
But there are few options once grapes are picked if vineyard methods weren't enough to keep sugars low. A winemaker can blend the fermented wine with a lower-alcohol wine. They can add water, but that is illegal in some countries and less than ideal because it dilutes everything in the wine. A winery can use modern techniques such as reverse osmosis or spinning cone distillation, but those techniques are expensive and some argue they dumb down flavors in the wine.
There are several genetically modified yeast strains that can produce lower alcohol wines, but genetically modified organisms remain controversial. So senior research scientist Cristian Varela and his team went looking for a strain found in nature.
The yeast in question, Metschnikowia pulcherrima, was singled out from a pool of about 40 different species chosen for their ability to ferment sugar and produce ethanol under anaerobic conditions during four days of culture. But Metschnikowia pulcherrima, or AWRI 1149, achieved the greatest balance of lower alcohol and negative side effects.
The results, though noteworthy, are not without some issues. The team observed that the Chardonnay samples showed higher levels of ethyl acetate, which can lead to nail polish aromas in finished wines. And while AWRI 1149 is adept at consuming sugars, it dies before the full fermentation process is complete, so a secondary yeast (the tried and true Saccharomyces cerevisiae), was employed to ferment the wine dry.
“The developments are interesting, but in a larger winery setting, sequential fermentation adds a step that some might not wish to employ when they already have several fermentations going on at the same time," said Melissa Burr, winemaker at Stoller Vineyards in Willamette Valley.
Dr. Linda Bisson, professor of yeast microbiology and functional genetics at U.C. Davis, warns that while the new yeast might prove to be an effective tool in the management of alcohol in wine, winemakers should be wary of the “translatability of laboratory-scale fermentation data to production conditions." She said one challenge is that in fermentations with several yeasts present, other species of metschnikowia could take charge.
Varela agreed the next challenge is to prove the yeast can work on a large scale. “Although our results suggest that M. pulcherrima will be able to cope with these conditions and M. Pulcherrima is found in wine fermentations, we need to confirm lab results at a pilot scale.”