Abstract
Wine biological aging is characterized by the development of yeast strains that form a biofilm on the wine surface after alcoholic fermentation. These yeasts, known as flor yeasts, form a velum that protects the wine from oxidation during aging. Thirty-nine velums aged from 1 to 6 years were sampled from “Vin jaune” from two different cellars. We show for the first time that these velums possess various aspects in term of color and surface aspects. Surprisingly, the heterogeneous velums are mostly composed of one species, S. cerevisiae. Scanning electron microscope observations of these velums revealed unprecedented biofilm structures and various yeast morphologies formed by the sole S. cerevisiae species. Our results highlight that different strains of Saccharomyces are present in these velums. Unexpectedly, in the same velum, flor yeast strain succession occurred during aging, supporting the assumption that environmental changes are responsible for these shifts. Despite numerous sample wine analyses, very few flor yeasts could be isolated from wine following alcoholic fermentation, suggesting that flor yeast development results from the colonization of yeast present in the aging cellar. We analyzed the FLO11 and ICR1 sequence of different S. cerevisiae strains in order to understand how the same strain of S. cerevisiae could form various types of biofilm. Among the strains analyzed, some were heterozygote at the FLO11 locus, while others presented two different alleles of ICR1 (wild type and a 111 bp deletion). We could not find a strong link between strain genotypes and velum characteristics. The same strain in different wines could form a velum having very different characteristics, highlighting a matrix effect.
Highlights
Wine is produced through the action of a complex microbial consortium (Petruzzi et al, 2017) composed among others of numerous non-Saccharomyces yeast species and a high diversity of S. cerevisiae (Capece et al, 2016)
Little information exists on the dynamics of yeast from alcoholic fermentation until the end of the biological aging process
Our results show that Savagnin wine velums present very different characteristics never reported before in terms of color and morphology
Summary
Wine is produced through the action of a complex microbial consortium (Petruzzi et al, 2017) composed among others of numerous non-Saccharomyces yeast species and a high diversity of S. cerevisiae (Capece et al, 2016). Flor yeast or flor velum yeasts can grow at the surface of different wines. These flor yeasts can be found in very specific wine processes known as biological aging practiced in Spain (Andalusia), Italy (Sardinia), Hungary and France (Jura) to produce Xeres, Vernaccia di Oristano, Szamorodni, and Vin Jaune wines, respectively. In the classical wine process, yeast dies in the absence of sugar and oxygen at the end of the alcoholic fermentation. In the case of biological aging, the common characteristic of these wines is that after alcoholic fermentation, they are transferred into barrels, leaving
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