Researchers Indentify Yeast to Preserve Wine Flavor

The discovery of special yeast that produce a lower level of alcohol will likely help preserve the flavor of wine, according to new research published in the journal Applied and Environmental Microbiology.

WASHINGTONThe discovery of special yeast that produce a lower level of alcohol will likely help preserve the flavor of wine, according to new research published in the journal Applied and Environmental Microbiology.

The alcoholic content of wine has crept up gradually during the last 10 to 15 years, from around 12% to beyond 15%. What might sound trivial to aficionados of hard liquor is seen by some oenophiles as a disturbing trend, threatening the flavor and character of some wines. In addition, issues of public health, as well as taxes (in some countries, on alcoholic content), have created a need for approaches to lowering alcohol content.

Corresponding author Cristian Varela of the Australian Wine Research Institute, Adelaide, South Australia, and a team of Australian researchers began their investigation with a systematic screening of non-Saccharomyces yeast as a means of achieving such a reduction. The investigators evaluated 50 different isolates from 40 species and 24 genera for their capacity to produce wine with reduced ethanol concentration. They chose the most successful of these yeasts, Metschnikowia pulcherrima AWRI1149, for experiments in which it was set to work separately on Chardonnay and Shiraz musts.

Once the slower-growing Metschnikowia yeasts had consumed 50% of the sugar, S. cerevisiae were added to the mix to complete the process. This sequential inoculation" reduced the alcohol content in Shiraz from 15% to 13.4% (and somewhat less in Chardonnay). Controls not inoculated with non-Saccharomyces strains did not produce reduced alcohol content, according to the report.

"This reduction in alcohol will be of great benefit to the industry," said Louisa Rose, director of the Australian Wine Research Institute. It is using techniquessequential fermentationthat can easily be used in the winery on a commercial scale."

Previous studies investigating the effects of non-Saccharomyces yeasts on alcoholic fermentation have focused on few species and been concerned principally with the formation of the flavor compounds that might impact negatively on wine quality. None of these led to reductions in alcohol content as substantial as those reported.

The rise in alcohol content in wine has resulted from later harvesting of red grapes. This allows the tanninsresponsible for astringency and bitternessto soften. In some varieties, it helps minimize the presence of off-flavors, such as methoxypyrazines (green pepper/asparagus sensory notes). But on the downside, the boost in alcohol content reduces aroma and flavor intensity, as well as otherwise impairing the oenological experience. Reducing the alcohol would enable the best of both worlds. It would also reduce consumer costs in countries where alcohol consumption is taxed, and accede to national and international public health recommendations to lower the alcohol content of alcoholic beverages, such as wine.

Wine lovers have another reason to celebrate: recent research shows consuming high levels of flavonoids and other compounds found in wine may help ward off the onset of type 2 diabetes.

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