Tscheik, G. | bioRxiv Science

bioRxiv2024

Pure yeasts selected from fermenting pear juice from the Lower Austrian Mostviertel region and their suitability for pear wine production

If spontaneous fermentation is not carried out, commercially available pure yeasts, which are actually intended for the production of wines from grapes, are often used for the production of pear wines. Pear juice is clearly different from grape juice, e.g. due to the significantly greater difference in the ratio of fructose to glucose or the absence of tartaric acid. For this reason, the commercially available pure yeasts may be suboptimal for pear wine production. They were therefore compared with yeasts isolated from pear juice that had been purely cultivated with regard to their suitability for pear wine production. Overall, the yeasts isolated from fermenting pear juice proved to be more suitable for pear wine production. This is not only the result of the tasting of the wines fermented in 25-litre glass flasks, but also follows very clearly from the multivariate comparison both for the basic chemistry and for the spectrum of aroma components. Density and malic acid concentration were higher in wines produced with yeasts selected from fermenting pear juice. More substances from the "fruity" and especially "fruity-sweet" flavour groups were found in these wines in comparatively higher concentrations. For pear wine production, it is therefore advisable to isolate suitable yeasts from pear juice for pure cultivation.

microbiology↗

bioRxiv2018

Fermentation characteristics of mead and wine generated by yeasts isolated from beehives of two Austrian regions

Mead is a traditional alcoholic beverage that is produced by fermentation of diluted honey. The mead quality is primarily influenced by the honey variety, although the yeast microflora as the main catalyst of alcoholic fermentation also plays a significant role in the organoleptic and chemical quality of the final product. The impact of the indigenous honey associated-yeasts on the mead properties has scarcely been investigated. To fill this gap the main objective of this work was to assess the metabolic properties of the yeasts isolated from honey and pollen from beehives of northeast Austria.\n\nThe biodiversity was low and only two yeast species were identified, Zygosaccharomyces rouxii and Candida apicola. The fermentation potentials of these yeasts were estimated in two media, grape juice (since yeasts isolated from honey may be useful for sweet wine production) and diluted honey of similar sugar concentration, and compared with those of the reference strains Saccharomyces cerevisiae; S. uvarum and S. eubayanus. Depending on the fermentation substrate, yeasts differed with respect to their metabolic power, fermentation rate, sugar utilization and production of glycerol and organic acids. During mead fermentation Saccharomyces species showed the highest metabolic turnover, while the fermentation rate did not differ significantly. Addition of assimilable nitrogen to the diluted honey enhanced fermentation rate of S. cerevisiae, but not of the other species. Fermentation of grape juice occurred much faster than that of diluted honey and differences between yeasts were more pronounced. The S. cerevisiae commercial wine strain, adapted to high alcohol concentrations, and S. eubayanus outperformed the others, S. uvarum was comparable with Z. rouxii, while C. apicola had the lowest fermentation rate. Fructophily of Z. rouxii and to a lesser degree of C. apicola was observed in both media. An increased production of glycerol was achieved by S. eubayanus in both media and by C. apicola during the fermentation of honey must. A commercial S. cerevisiae strain, S. eubayanus and Z. rouxii were able to metabolize malic acid in wine. In mead, the S. eubayanus and S. uvarum yeasts showed the tendency of increasing the level of malic acid. Aroma profile depended profoundly on yeast species. This study demonstrates that the composition and complexity of the fermentation substrate determines the activity and the final metabolic outcomes of the studied yeasts.

microbiology↗