Contributions of species to Pinot Noir microbial terroir in Oregon's Willamette Valley wine region.

UNLABELLED

The apiculate yeast genus has appeared frequently in enological research for more than 100 years, mostly focused upon the species due to its notable capacity to cause spoilage. Recently, there has been increased research into the potential benefits of other species, such as in producing more complex wines. Furthermore, large-scale DNA sequencing-based (metabarcoding) vineyard ecology studies have suggested that species may not be evenly distributed. To address potential differences across geographical areas in Oregon, we sampled extensively from 12 vineyards within the Willamette Valley American Viticultural Area (AVA), across 2 sub-AVAs (Eola-Amity Hills and Yamhill-Carlton). Metabarcoding was then used to assess the contribution of to the grape berry fungal community and the impact of wine processing on diversity. While 6 of the 23 recognized species were present on Pinot Noir grapes in the Willamette Valley AVA, differences between vineyards were driven by the abundance of . Significant positive correlations between the amount of present in must and at cold soak, and then cold soak to early ferment were observed. While intuitive, it is worth noting that no prior studies have observed this across such a large number of grape samples from different vineyards. Our results provide clear evidence that the abundance of on grapes may be an important predictor of potential impacts on wine quality, particularly if performing cold soak, which acts as an enrichment step.

IMPORTANCE

yeasts are frequently found in uninoculated wine fermentations, and depending upon the species present, their contributions to the wine may be positive or negative. We found that in Oregon's Willamette Valley, the most common species of in Pinot Noir vineyards was the known spoilage organism, . This species was one of the strongest contributors to differences in fungal communities between different vineyards and was enriched during typical Pinot Noir processing. These results support as an integral and functional component of vineyard "microbial terroir" within Oregon.