Development of bioprospecting tools for oenological applications

Abstract

Wine is the result of a complex biochemical process. From a microbiological point of view, the grape berry is characterised by a heterogeneous microbiota composed of different microorganisms (yeasts, bacteria and filamentous fungi) which will play a predominant role in the quality of the final product. At this level, yeasts play a predominant role in the chemistry of wine, as they actively participate in alcoholic fermentation, a biochemical process where the sugars in the grapes are transformed into ethanol and carbon dioxide, producing at the same time a large number of additional by-products.

Currently, the demand for indigenous yeast starters, potentially adapted to a defined grape must and reflecting the biodiversity of a particular region, is increasing, supporting the idea that indigenous yeast strains can be associated with a ‘terroir’. Several authors have thus highlighted the action of some non-Saccharomyces species in the chemical composition of wine. Nevertheless, it is still recognised that non-Saccharomyces strains have a low fermentation ability, as they are not able to fully metabolise the sugars in the grape juice and therefore produce low amounts of ethanol, although they have several oenological properties that are fundamental for the organoleptic properties of wine. Thus, the use of a mixed non-Saccharomyces/Saccharomyces ferment, capable of mimicking natural biodiversity, could be a valid alternative to spontaneous fermentation, given the capacity of this ferment to increase the organoleptic properties of the wine and to minimise microbial alterations.

The objectives of this work were to prospect and identify precisely genetically yeasts of interest for the production of fermented beverages according to an innovative protocol in several swiss vineyards, to establish a methodology to phenotypically characterise the isolated yeasts and finally to try to develop a procedure to accompany the winegrowers in their approach of mixed saccharomyces and non-saccharomyces yeasts use.