Inoculation of grape musts with single strains of Saccharomyces cerevisiae yeast reduces the diversity of chemical profiles of wines.

Christian Philipp,Bahareh Bagheri,Phillip Eder,Mathabatha Evodia Setati,Micha Horacek,Florian Franz Bauer,Luca Cocolin

doi:10.1371/journal.pone.0254919

Abstract

Anecdotal evidence suggests that spontaneous alcoholic fermentation of grape juice is becoming a more popular option in global wine production. Wines produced from the same grape juice by inoculation or spontaneous fermentation usually present distinct chemical and sensorial profiles. Inoculation has been associated with more similar end-products, a loss of typicity, and lower aroma complexity, and it has been suggested that this may be linked to suppression of the local or regional wine microbial ecosystems responsible for spontaneous fermentations. However, whether inoculated fermentations of different juices from different regions really end up with a narrower, less diverse chemical profile than those of spontaneously fermented juices has never been properly investigated. To address this question, we used grape juice from three different varieties, Grüner Veltliner (white), Zweigelt (red), and Pinot noir (red), originating from different regions in Austria to compare spontaneous and single active dry yeast strains inoculated fermentations of the same grape samples. The chemical analysis covered primary metabolites such as glycerol, ethanol and organic acids, and volatile secondary metabolites, including more than 40 major and minor esters, as well as higher alcohols and volatile fatty acids, allowing an in depth statistical evaluation of differences between fermentation strategies. The fungal (mainly yeast) communities throughout fermentations were monitored using automated ribosomal intergenic spacer analysis. The data provide evidence that inoculation with single active dry yeast strains limits the diversity of the chemical fingerprints. The fungal community profiles clearly show that inoculation had an effect on fermentation dynamics and resulted in chemically less diverse wines.

Highlights

The spontaneous fermentation process is often characterized by successional development of yeast genera, species and strains, with the final stages of fermentation usually dominated by strains of Saccharomyces cerevisiae
The fermentation dynamics can be seen in S1 Fig. Overall, all inoculated juices fermented dry and the inoculated Gruner Veltliner B and Zweigelt fermented significantly faster than the spontaneously fermented equivalents while the fermentation curves of the spontaneous fermentations for all variants show a delayed alcoholic fermentation at the beginning and in the middle section
The Gruner Veltliner B that had low yeast assimilable nitrogen (YAN) levels in the must become stuck and fermentations were terminated with 60 and 29 g/L residual sugar, respectively, and contained significantly lower ethanol levels compared to their inoculated variants

Summary

Introduction

Alcoholic fermentation traditionally occurs spontaneously and it is initiated by a diverse community of indigenous yeasts of the genera Hanseniaspora, Pichia, Metschnikowia, Candida, Torulaspora, Rhodotorula, Cryptococcus, Lachancea, Zygosaccharomyces and most importantly, Saccharomyces [9]. The spontaneous fermentation process is often characterized by successional development of yeast genera, species and strains, with the final stages of fermentation usually dominated by strains of Saccharomyces cerevisiae. Since the 1960s, alcoholic fermentation on an industrial scale is typically conducted through inoculation with commercial Active Dry Yeast (ADY) strains [11,12,13,14] that have high fermentation capacity and proven capability to produce wines with consistent quality and predictable aroma compositions. To the best of our knowledge, no studies have provided direct evidence for such reduction in wine flavour diversity

Methods

Results

Discussion

Conclusion