Selection of Non-Saccharomyces Yeasts from Extreme Oenological Environments for Potential Use in Winemaking

This study evaluated the oenological potential of two non-<i>Saccharomyces</i> yeast strains, <i>Hanseniaspora opuntiae</i> TR-5 and <i>Zygosaccharomyces bailii</i> L-25, isolated from extreme winemaking environments in southern Spain. Out of 156 yeast isolates screened from high-sugar musts and flor yeast biofilms, strains were selected based on their <i>β</i>-glucosidase activity, killer phenotype, and ethanol production, traits associated with aroma release and microbial competition. Fermentation trials on sugar-rich synthetic medium showed that both <i>H. opuntiae</i> and <i>Z. bailii</i> achieved ethanol yields of 10% <i>v</i>/<i>v</i> and residual sugars at 4 g/L. Co-culture and sequential inoculation, with <i>H. opuntiae</i> introduced first and <i>Z. bailii</i> added on day four, resulted in complete alcoholic fermentation and a reduction in undesirable acetoin levels compared to single-strain fermentations. These findings highlight the practical potential of using selected non-<i>Saccharomyces</i> strains in sequential fermentations to improve aroma complexity, fermentation reliability, and sensory quality in wines, even in the absence of <i>Saccharomyces cerevisiae</i>. The application of these strains offers a novel approach for precision oenology and varietal expression in challenging musts.