Technologies and strategies for the production of lower alcohol wine
There is growing public and consumer interest in wines with lower alcohol concentration that maintain robust aroma and flavour profiles. Producers may also face financial penalties for higher alcohol wines in markets where taxes are levied on the basis of alcohol concentration.
The microbial biodiversity of spontaneous fermentations contains great potential for shaping wine style, including the production of wine with reduced alcohol concentration. Harnessing this diversity in controlled, inoculated ferments may provide winemakers with simple, cost-effective and low risk strategies for tailoring wines to market demands. In the context of this project, non-conventional yeast (yeast other than S. cerevisiae) can be used to remove some fermentable sugar from must prior to inoculation with S. cerevisiae.
Harnessing the potential of non-conventional yeasts for lower-alcohol wine production
A Metschnikowia pulcherrima strain and a Saccharomyces uvarum strain have been identified as able to produce wine with reduced ethanol concentration when sequentially inoculated with a wine strain of S. cerevisiae. When used in combination both strains enabled an additional reduction of wine ethanol concentration compared to the same must fermented with either strain alone. While wines fermented with M. pulcherrima alone showed certain volatile compounds likely to affect wine aroma negatively, wines fermented with S. uvarum or a combination of both strains did not show these potentially detrimental compounds.
Given the great diversity of non-conventional yeasts it is not surprising that some have the potential to oxidise grape sugars, through biosynthetic pathways S. cerevisiae is not able to utilise, and therefore decrease ethanol concentration in wine. Through screening of nearly 50 different non-Saccharomyces yeasts, one Torulaspora delbrueckii strain and one Zygosaccharomyces bailii strain were identified as suitable for the production of wine with reduced ethanol content when provided with minimal aeration. A proof-of-concept sequential inoculation study of these strains in a synthetic grape juice observed ethanol reductions of 1.5% v/v and 2.0% v/v respectively in the final wine compared to a S. cerevisiae fermented control.