A team of Australian researchers has taken a giant step towards controlling a growing problem in the wine community.   They have identified special yeast that produce a lower level of alcohol, helping to preserve the flavor. Their research is published ahead of print in the journal Applied and Environmental Microbiology.
 
The alcoholic content of wine has crept gradually northward in the last 10-15 years, from 12-12.5 percent to beyond 15 percent. 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. That, plus issues of public health, as well as taxes (in some countries, on alcoholic content), have created a need for approaches to lowering alcohol content.
 
The investigation began with a systematic screening of non-Saccharomyces yeast as a means of achieving such a reduction, says corresponding author Cristian Varela of the Australian Wine Research Institute, Adelaide, South Australia. The investigators evaluated 50 different isolates from 40 species and 24 genera for their capacity to produced 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 percent 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 percent to 13.4 percent (and somewhat less in Chardonnay). Controls not inoculated with non-Saccharomyces strains did not produce reduced alcohol content, according to the report.
 
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 he reported, says Varela.
 
A copy of the manuscript can be found online at http://bit.ly/asmtip0114f. The final version of the article is scheduled for the March 2014 issue of Applied and Environmental Microbiology.