Consumers are increasingly interested in trying unique wine experiences, seeking wines that reflect a sense of place. One tool with which to achieve such wines is uninoculated fermentations, performed by the diverse native yeast communities to boost wine sensory attributes. Many of these native yeasts can ferment grape juice even without the addition of commercial yeast. This is how wines are produced with special sensory attributes (aroma, texture, and length) that are part of what some winemakers call the ‘terroir’.
The diversity of yeast in fermentations starts in the vineyard and can be modified by various factors including climate (rain and temperature) and viticultural practices (fungicide applications). Applications of fungicides are necessary to control the multiple grapevine diseases caused by fungi and oomycetes every season which cause multi-million-dollar losses to the wine industry. However, whilst this keeps the developing bunches healthy, native yeast populations become off-target organisms whose populations are affected by the sprays.
Our hypothesis is that organic vineyard practices might drive less diverse yeast populations as they rely on broad spectrum fungicides; whilst conventional vineyards might contain more diverse populations as the products used have specific sites of action. Therefore, in this study, we characterised the yeast communities identified from biodynamic and conventionally grown Riesling grape washes, juice, and fermentation. We aimed to elucidate the link between these treatments and the observed yeast diversity.
Both biodynamic and conventional grapes were manually harvested and split into separate treatments. Grape samples were collected and washed to harvest fungal species and both treatments were also processed by crushing in separate batches. The resulting juice was split into 6 replicates which were incubated at 23 °C and sampled over three weeks (uninoculated fermentations). ITS1 Illumina sequencing was used to identify the different yeast species in each sample and their relative abundance.
We found that the conventional grape washes and juice had the highest diversity. However, we observed a shift in the biodynamic treatment during fermentation, with Saccharomyces cerevisiae being the dominant species from mid-fermentation. This information could help tailor fungicide spraying schemes to optimise their effectiveness, whilst maintaining vineyard ecological balance.