Novel Methods to Manipulate Autolysis in Sparkling Wine: Effects on Yeast.

Gail B Gnoinski,Gail B Gnoinski,Terry L Pinfold,Dugald C Close,Simon A Schmidt,Karsten Goemann,Fiona L Kerslake,Fiona L Kerslake

doi:10.3390/molecules26020387

Abstract

Sparkling wine made by the traditional method (Méthode Traditionelle) develops a distinct and desirable flavour and aroma profile attributed to proteolytic processes during prolonged ageing on lees. Microwave, ultrasound and addition of β-glucanase enzymes were applied to accelerate the disruption of Saccharomyces cerevisiae, and added to the tirage solution for secondary fermentation in traditional sparkling winemaking. Scanning electron microscopy and flow cytometry analyses were used to observe and describe yeast whole-cell anatomy, and cell integrity and structure via propidium iodide (PI) permeability after 6-, 12- and 18-months post-tirage. Treatments applied produced features on lees that were distinct from that of the untreated control yeast. Whilst control yeast displayed budding cells (growth features) with smooth, cavitated and flat external cell appearances; microwave treated yeast cells exhibited modifications like ‘doughnut’ shapes immediately after treatment (time 0). Similar ‘doughnut’-shaped and ‘pitted/porous’ cell features were observed on progressively older lees from the control. Flow cytometry was used to discriminate yeast populations; features consistent with cell disruption were observed in the microwave, ultrasound and enzyme treatments, as evidenced by up to 4-fold increase in PI signal in the microwave treatment. Forward and side scatter signals reflected changes in size and structure of yeast cells, in all treatments applied. When flow cytometry was interpreted alongside the scanning electron microscopy images, bimodal populations of yeast cells with low and high PI intensities were revealed and distinctive ‘doughnut’-shaped cell features observed in association with the microwave treatment only at tirage, that were not observed until 12 months wine ageing in older lees from the control. This work offers both a rapid approach to visualise alterations to yeast cell surfaces and a better understanding of the mechanisms of yeast lysis. Microwave, ultrasound or β-glucanase enzymes are tools that could potentially initiate the release of yeast cell compounds into wine. Further investigation into the impact of such treatments on the flavour and aroma profiles of the wines through sensory evaluation is warranted.

Highlights

This article is an open access articleSparkling wine made by the traditional method (Méthode Traditionelle) develops a distinct and desirable flavour and aroma profile, frequently described as ‘autolytic character’, that is attributed to proteolytic processes that occur during prolonged ageing in contact with yeast cells [1,2,3]
Our findings indicate a slower process, relative to microwave and ultrasound, but consistent with the findings of Palomero et al [26] and others [22,23] we found high levels of cavitated β-glucanase enzyme treated cells, relative to the control treatment, that may be indicative of release of polysaccharides arising from cell wall disruption
The addition of yeast treatments, that have the potential for earlier release of cellular components, to the tirage solution could reduce the time required on lees to achieve the characteristics of mature sparkling wine

Summary

Introduction

Sparkling wine made by the traditional method (Méthode Traditionelle) develops a distinct and desirable flavour and aroma profile, frequently described as ‘autolytic character’, that is attributed to proteolytic processes that occur during prolonged ageing in contact with yeast cells (lees) [1,2,3]. The traditional method of sparkling wine production encompasses two fermentation processes. A primary fermentation to produce a base wine. This base wine receives a subsequent addition of yeast and sugar (liqueur de tirage), often combined with an adjuvant mixture comprised of bentonite, alginate and nutrients, which initiates secondary fermentation. Secondary fermentation is generally complete in two to three months after which lengthy maturation in contact with yeast is considered necessary to develop sensorial complexity [1,4,5,6,7]

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