Alterations in yeast species composition of uninoculated wine ferments by the addition of sulphur dioxide

Uninoculated wine fermentations are conducted by a consortium of wine yeast and bacteria that establish themselves either from the grape surface or from the winery environment. Of the additives that are commonly used by winemakers, sulphur dioxide (SO₂) represents the main antimicrobial preservative and its use can have drastic effects on the microbial composition of the fermentation. In order to explore the effect of SO₂ addition on the yeast microbiota during uninoculated Chardonnay wine, meta-barcoding (phylotyping) analysis was used to assess the population dynamics of wine produced across two successive vintages using a range of pre-ferment SO₂ levels.

Project layout

Chardonnay grape juice from 2018 and 2019 was treated with a variety of SO₂ concentrations ranging up to 100 mg/L and was then allowed to undergo fermentation, with the yeast community structure being assessed via high-throughput meta-barcoding (phylotyping).

Results

• While the addition of SO₂ was shown to select against the presence of many species of non-Saccharomyces yeasts, there was a clear and increasing selection for the species Hanseniaspora osmophila as concentrations of SO₂ rose above 40 mg/L in fermentations from both vintages.
• Chemical analysis of the wines resulting from these treatments showed significant increases in acetate esters, and specifically the desirable aroma compound 2-phenylethyl acetate, that accompanied the increase in abundance of H. osmophila.

Significance of the study

The ability to modulate the yeast community structure of an uninoculated ferment and the resulting chemical composition of the final wine, as demonstrated in this study, represents an important tool for winemakers to begin to be able to influence the organoleptic profile of uninoculated wines.

Reference

Cuijvers, K.; Van Den Heuvel, S.; Varela, C.; Rullo, M.; Solomon, M.; Schmidt, S.; Borneman, A. Alterations in Yeast Species Composition of Uninoculated Wine Ferments by the Addition of Sulphur Dioxide. Fermentation 2020, 6, 62. https://doi.org/10.3390/fermentation6020062

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