Osmotolerant yeasts isolated from Tokaj wines

Vinification without Saccharomyces: Interacting Osmotolerant and "Spoilage" Yeast Communities in Fermenting and Ageing Botrytised High-Sugar Wines (Tokaj Essence)

The conversion of grape juice to wine starts with complex yeast communities consisting of strains that have colonised the harvested grape and/or reside in the winery environment. As the conditions in the fermenting juice gradually become inhibitory for most species, they are rapidly overgrown by the more adaptable Saccharomyces strains, which then complete the fermentation. However, there are environmental factors that even Saccharomyces cannot cope with. We show that when the sugar content is extremely high, osmotolerant yeasts, usually considered as “spoilage yeasts“, ferment the must. The examination of the yeast biota of 22 botrytised Tokaj Essence wines of sugar concentrations ranging from 365 to 752 g∙L⁻¹ identified the osmotolerant Zygosaccharomyces rouxii, Candida (Starmerella) lactis-condensi and Candida zemplinina (Starmerella bacillaris) as the dominating species. Ten additional species, mostly known as osmotolerant spoilage yeasts or biofilm-producing yeasts, were detected as minor components of the populations. The high phenotypical and molecular (karyotype, mtDNA restriction fragment length polymorphism (RFLP) and microsatellite-primed PCR (MSP-PCR)) diversity of the conspecific strains indicated that diverse clones of the species coexisted in the wines. Genetic segregation of certain clones and interactions (antagonism and crossfeeding) of the species also appeared to shape the fermenting yeast biota.

Biological diversity of Saccharomyces yeasts of spontaneously fermenting wines in four wine regions: comparative genotypic and phenotypic analysis

Combination of molecular genetic analysis (karyotyping, PCR-RFLP of MET2, the ITS1-ITS2 region and the NTS region) and physiological examination (melibiose and mannitol utilization, sugar-, ethanol- and copper tolerance, killer activity, fermentation vigor and production of metabolites) of yeasts isolated from spontaneously fermenting wines in four wine regions revealed very high diversity in the Saccharomyces cerevisiae populations. Practically each S. cerevisiae isolate showed a unique pattern of properties. Although the strains originating from the same wine were quite similar in certain traits, they showed diversity in other properties. These results indicate that alcoholic fermentation in grape wines is performed by highly diverse yeast consortia rather than by one or two dominating strains. The less frequent Saccharomyces uvarum strains were less diverse, showed lower karyotype variability, were Mel(+), Man(+), more sensitive to 60% sugar, and ethanol or copper in the medium. They produced less acetic acid and fermented better at 14 degrees C than most of the S. cerevisiae isolates, but certain S. cerevisiae strains showed comparably high fermentation rates at this temperature, indicating that it is not a general rule that S. uvarum ferments better than S. cerevisiae at low temperatures. The segregation of certain traits (melibiose utilization, mannitol utilization and copper resistance) in both species indicates that the genomes can easily change during vegetative propagation. The higher diversity among the S. cerevisiae isolates suggests that the S. cerevisiae genome may be more flexible than the S. uvarum genome and may allow more efficient adaptation to the continuously changing environment in the fermenting wine.