Combined use of Wallerstein and Zygosaccharomyces bailii modified differential media to isolate yeasts for the controlled reduction of volatile acidity of grape musts and wines
The level of acetic acid, the main component of volatile acidity, is critical for wine quality. Winemakers have
been using a refermentation process to lower the concentration of acetic acid of wines with high volatile acidity,
whichconsistsinmixingtheacidicwinewithfreshlycrushedgrapesormarcsinaproportionofnomorethan
20-30% (v/v). Though this process implies low costs it harbors the risk of unexpected and detrimental effects on
refermented wines. Thus, one challenge to find new solutions for the reduction of excessive volatile acidity is
the selection of yeast from refermentation processes of acidic wines to use as starters in a controlled biological
process.To this end we setup an isolation protocolwithWallerstein Laboratory Nutrient Agar(WL)to select
yeast strains from refermentation processes of acidic wines carried atthe winery scale. Among the isolates
obtained, 135 were then randomly selected, based on the different colony color pattern and size, and tested for
their ability to consume acetic acid in the presence of glucose. For this purpose we used a modified version of a
Zygosaccharomycesbailiidifferentialmediumcontainingaceticacidandglucose.Characterizationoftheisolates
obtained in this medium by fingerprinting with primer T3B confirmed three Saccharomyces strains and one nonSaccharomyces
strain as predicted by WL and L-Lysine media. Our previous studies revealed that the yeast
strains selected by this approach are adequate forthe correction of acidic musts and wines with excessive levels
of volatile acidity.This work received financial support from the IBB/CGB – UTAD and was supported by FEDER
throughPOFC – COMPETEand byPortuguese funds from FCTthrough the projectPEst-OE/BIA/UI4050/2014.info:eu-repo/semantics/publishedVersio
