Browsing by Author "Nutt, John"

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    Multispecies interactions in a simplified wine yeast consortium
    (Stellenbosch : Stellenbosch University, 2018-03) Nutt, John; Bauer, Florian; Setati, Mathabatha Evodia; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.
    ENGLISH ABSTRACT: Over the last two decades various studies have evaluated the impact of non-Saccharomyces (NS) yeasts on alcoholic fermentation of wine, the chemical imprint they leave in the wine and how this affects wine quality. These NS yeasts are either present naturally in the grape must or inoculated together with Saccharomyces cerevisiae, but little is known about how these NS interact with each other and with S. cerevisiae and how these interactions might influence the presences of other yeast during fermentation and ultimately affect the contribution of each yeast to the wine. In recent years, several strains of the species, Torulaspora delbrueckii, Pichia kluyveri, Metschnikowia pulcherrima and Lachancea thermotolerans have been commercialized. The availability of such commercial preparations allows winemakers to perform mixed-culture fermentations through different inoculation strategies. Research has evaluated co-inoculations and sequential inoculations between NS and S. cerevisiae, but grape must is a complex ecosystem with a large variety of indigenous yeasts that partake during fermentation. Understanding how various yeasts interact within such a larger matrix is challenging, but will make an essential contribution to sound decision making in wineries. This study was designed to better understand how NS yeasts perform individually and how their behaviour might differ in the presence of one or more other yeasts and what effect this might have on the final wine. Three commercial NS yeasts strains and one S. cerevisiae yeast strain were used to determine how these yeasts interact and how these interactions might alter the chemical composition of wine. Fifteen inoculations scenarios, including mono-culture, co-culture and combinations of three and ultimately a consortium containing all four yeasts were performed. Fermentations were carried out in synthetic grape juice at both 15°C and 25°C. The data showed significant variations in the cell densities of all species through-out fermentation depending on the nature of the co-inoculated species and the environmental conditions. These changes in population dynamics also had a clear impact on the concentration of and types of aromatic compounds produced. Chenin blanc wines made with the consortium of all four yeasts, S. cerevisiae and spontaneous fermentations, showed distinct chemical profiles. However, no correlation was found, regarding population dynamics or aroma profiles of the wines, between the synthetic wine and the Chenin blanc wines both derived from the consortium inoculation. This study provides the foundation for future work on understanding how multiple species (more than two yeasts) interact within fermentations and how this will affect wine quality. It also provides a better understanding of how one yeast can suppress the presence of other yeasts and how different temperatures might affect the presence of each yeasts and how this might influence the interactions between the yeasts.