Identification of flocculant wine yeast strains with improved filtration-related phenotypes through application of high-throughput sedimentation rate assays

Cristian Varela,Damian Espinase Nandorfy,Chris Curtin,Caroline Bartel,Anthony Borneman,Simon Schmidt

doi:10.1038/s41598-020-59579-y

Cristian Varela, Damian Espinase Nandorfy + Show 4 more

Open Access

https://doi.org/10.1038/s41598-020-59579-y

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Abstract

In most yeast-driven biotechnological applications, biomass is separated from the aqueous phase after fermentation or production has finished. During winemaking, yeasts are removed after fermentation by racking, filtration, or centrifugation, which add costs to the overall process and may reduce product yield. Theoretically, clarification and filtration can be aided through use of yeast strains that form flocs due to cell-cell binding, a process known as flocculation. However, because early flocculation can cause stuck/sluggish fermentations, this phenotype is not common amongst commercially available wine yeasts. In this study we sought to identify wine strains that exhibit late-fermentation flocculant behaviour using two complementary approaches; a high-throughput sedimentation rate assay of individual strains and a competitive sedimentation assay using a barcoded yeast collection. Amongst 103 wine strains, several exhibited strong sedimentation at the end of the wine fermentation process under various environmental conditions. Two of these strains, AWRI1688 and AWRI1759, were further characterised during red winemaking trials. Shiraz wines produced with both strains displayed improved filtration-related properties. AWRI1759 produced wines with greater filterability, whereas AWRI1688 enabled the recovery of larger wine volumes after racking. Thus, this study demonstrates the effective use of sedimentation screening assays to identify wine yeasts with practical winemaking applications.

Highlights

In most yeast-driven biotechnological applications, biomass is separated from the aqueous phase after fermentation or production has finished
Flocculins are the products of the FLO gene family in S. cerevisiae, which can be subdivided into two groups[11]
An additional member of the family, FLO8 encodes a transcriptional activator of FLO1, FLO9, FLO11 and STA1, which encodes an extracellular glucoamylase[2,12]

Summary

Introduction

In most yeast-driven biotechnological applications, biomass is separated from the aqueous phase after fermentation or production has finished. Cell-to-cell binding resulting in the formation of large clusters of cells that settle to the bottom of the fermentation vessel is known as flocculation This behaviour involves a nonsexual, homotypic and reversible aggregation of yeast cells to form multicellular masses containing thousands of yeast cells[1,2,3]. Successful yeast flocculation facilitates clarification and downstream www.nature.com/scientificreports processing, simplifying enormously yeast removal from the final fermented product This reduces the need for time-consuming and expensive cell removal methods such as centrifugation and filtration[1,6]. Two additional minor flocculation phenotypes include a mannose insensitive (MI) phenotype[23], and, a phenotype in which flocculation is induced by ethanol[24]

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Conclusion