Overwintering of Vineyard Yeasts: Survival of Interacting Yeast Communities in Grapes Mummified on Vines

Abstract

The conversion of grape must into wine involves the development and succession of yeast populations differing in species composition. The initial population is formed by vineyard strains which are washed into the must from the crushed grapes and then completed with yeasts coming from the cellar environment. As the origin and natural habitat of the vineyard yeasts are not fully understood, this study addresses the possibility, that grape yeasts can be preserved in berries left behind on vines at harvest until the spring of the next year. These berries become mummified during the winter on the vines. To investigate whether yeasts can survive in these overwintering grapes, mummified berries were collected in 16 localities in the Tokaj wine region (Hungary-Slovakia) in early March. The collected berries were rehydrated to recover viable yeasts by plating samples onto agar plates. For the detection of minority species which would not be detected by direct plating, an enrichment step repressing the propagation of alcohol-sensitive yeasts was also included in the process. The morphological, physiological, and molecular analysis identified 13 basidiomycetous and 23 ascomycetous species including fermentative yeasts of wine-making relevance among the 3879 isolates. The presence of viable strains of these species demonstrates that the grapes mummified on the vine can serve as a safe reservoir of yeasts, and may contribute to the maintenance of grape-colonizing yeast populations in the vineyard over years, parallel with other vectors and habitats. All basidiomycetous species were known phylloplane yeasts. Three Hanseniaspora species and pigmented Metschnikowia strains were the most frequent ascomycetes. Other fermentative yeasts of wine-making relevance were detected only in the enrichment cultures. Saccharomyces (S. paradoxus, S. cerevisiae, and S. uvarum) were recovered from 13% of the samples. No Candida zemplinina was found. The isolates with Aureobasidium morphology turned out to belong to Aureobasidium subglaciale, Kabatiella microsticta, or Columnosphaeria fagi. The ascomyceteous isolates grew at high concentrations of sugars with Wickerhamomyces anomalus being the most tolerant species. Complex interactions including antagonism (growth inhibition, contact inhibition, competition for nutrients) and synergism (crossfeeding) among the isolates and with Botrytis cinerea shape the composition of the overwintering communities.

A Microtiter Plate Assay as a Reliable Method to Assure the Identification and Classification of the Veil-Forming Yeasts during Sherry Wines Ageing

“…In the case of the sequenced non-Saccharomyces yeast strains, Z. bailii did not grow on maltose, which is usually assimilated by Z. rouxii and R. mucilaginosa isolates grew on maltose, sucrose, lactose, which are not assimilated by R. minuta. These results are in accordance with those published in [14,21]. Thus, by applying the biochemical tests, we have ensured that these yeast strains have been satisfactorily identified (Table 4).…”

Bioprospecting for brewers: Exploiting natural diversity for naturally diverse beers

“…The authors observed ethanol to be an efficient inhibitor against fungal species as well, and most of their isolates were ascomycetes. Others have reported similar findings: While exploring the diversity of yeasts in wintering grapes, Sipiczki () noticed that high ethanol concentrations (>8% alcohol by volume (ABV); 4‐week incubation) with raffinose as carbon source effectively decreased the number of yeasts belonging to the Basidiomycota (from 69% of samples to 4%). From 270 mummified berries, he managed to isolate 23 different ascomycete and 13 different basidiomycete yeast species.…”

The ecology of insect–yeast relationships and its relevance to human industry

“…Indeed, hibernating wasps are one of the only known locations to reliably find these yeasts in the winter when sugar sources are nonexistent, and environments are hostile to cell growth. Yeasts can overwinter in some flowers and mummified fruits [82], but particularly in temperate regions this is likely to be the rare exception. Several species of nectar yeasts have been found to be abundant on bees [31] and in bee nests [37,83], and we speculate that beehives, like wasp foundresses, are important sites for the overwintering of yeasts.…”