Broadening your winemaking yeast portfolio: Identification of an SO2 tolerant non-Saccharomyces

Abstract

Non-Saccharomyces yeast are gaining winemaker interest worldwide because of their potential to improve wine quality (aroma, length, and texture). There are currently only a handful of commercial non-Saccharomyces strains available for winemakers to choose from and this project seeks to broaden their portfolio. Any new yeast isolate should be tolerant to the most common wine stressors e.g., pH, ethanol, and sulfur dioxide (SO2), a common antimicrobial and antioxidant. Additionally, their fermentation performance and desirable secondary metabolites are critical selection criteria. In this study, 480 indigenous yeasts were isolated from the Chalmers Merbein vineyard (Victoria, Australia) and identified by ITS sequencing. Nineteen of those isolates were chosen, based on species identification, for further assessment. These were screened for their ethanol and SO2 tolerance, using YPD agar spiked with increasing concentrations of both stressors. Only 13 isolates showed some degree of tolerance, and their ethanol production was evaluated in Chemically Defined Grape Juice Medium (CDGJM). Lastly, their SO2 tolerance was evaluated using CDGJM spiked with 20, 35, 50 and 65 ppm employing an automated fermentation platform. The most promising candidate, a Hanseniaspora opuntiae isolate, withstood 65 ppm SO2, similar to the Saccharomyces cerevisiae control. This isolate also consumed approximately 110 g/L of sugar and produced 6% v/v of ethanol. This isolate will be tested further for its assimilable nitrogen requirements and volatile production, with a view towards broadening the portfolio of winemaking starter cultures.