A model study for contributing factors of the fermentation of qvevri wine

We focus on the properties of traditional clay vessel-qvevri fermentation with three models: stainless steel tank-conventional fermentation (SC), stainless steel tank-spontaneous fermentation (SS) and qvevri-spontaneous fermentation (QS) using the same Auxerrois grapes that were harvested under organic growth practices. Each wine sample was aliquoted periodically through a 261-day fermentation and ripening period. Microflora were evaluated by a culture-and DNA-based approach: automated ribosomal intergenic spacer analysis (ARISA). To monitor alcohol fermentation, glucose, ethanol and glycerol were measured by enzymatic methods, while the major aromatic compounds were measured by GC/MS. The malic and lactic acid contents, to evaluate malolactic fermentation (MLF), were measured by HPLC. Mineral profiles were also analyzed by ICP/MS. Dynamic ex-changes of microflora were observed for yeasts and lactic acid bacteria depending on the use of both the starter yeast and qvevri vessel from ARISA analysis. The starter, Saccharomyces cerevisiae, could accelerate alcoholic fermentation and MLF due to the early prevalence of Oenococcus oeni. After 30 days of fermentation, the starter yeast was replaced by wild yeasts of Kloeckera apiculata and other S. cerevisiae strains. Under spontaneous conditions, alcoholic fermentation and MLF were boosted when using a qvevri in comparison to stainless steel. The sharp, tipped bottom of the qvevri could increase the density of microbial cells and promote fermentation. The production of aromatic compounds corresponded mainly to alcoholic fermentation. In contrast, the mineral components reflected the differences among vessels. In qvevri wines, the concentrations of Mn and Fe were 2-fold higher than those in stainless steel wines. Mn, in the presence of Fe, could promote the polymerization and polishing of tannins, which would result in qvevri wines having tastes similar to those of aged wine.