Are there regional micro-organisms, and can they be harnessed to produce regionally distinct wine styles?
Wine is a complex beverage that is comprised of thousands of metabolites that are produced through the action of yeasts and bacteria in fermenting grape must. To ensure a robust and reliable fermentation, most commercial wines are now produced through the inoculation of freshly crushed grapes with large amounts of the major wine yeast Saccharomyces cerevisiae. However, there is a growing trend towards the use of classical, uninoculated or ‘wild’ fermentations in which only those yeasts and bacteria that are naturally associated with the vineyard or winery perform the fermentation. This generally results in a far more complex progression of non-Saccharomyces fungal species, with S. cerevisiae only becoming dominant much later in the fermentation process. The varied metabolic contributions of these non-Saccharomyces species have been shown to impart desirable taste and aroma attributes to wild ferments when compared to their inoculated counterparts.
Metagenomic analysis of wild ferments
In order to map the microflora of spontaneous fermentation, metagenomic techniques have been used to monitor the progression of fungal species during a collection of wild fermentations from around Australia. Both amplicon-based internal transcribed spacer phylotyping and shotgun metagenomics were used to assess community structures, with the isolation, sequencing and de novo assembly of individual strains of the dominant wine-associated species also being performed in order to aid the analysis. Results so far support the view that uninoculated ferments begin with a diverse ecosystem of fungal species, but converge on the wine yeast S. cerevisiae as the fermentations progress. Notable differences have been seen between regions, vineyards and wineries and these can be broadly defined by the resulting microbial composition of the wild ferments. Accordingly, this study confirms that differences in these resident microflora between vineyards and wineries form part of the unique ‘terroir’ where grapes are sourced from and a wine is made, and may play a key role in defining unique regional expression of wine characteristics.