Suitability of indigenous <i>Saccharomyces cerevisiae</i> strains isolated from spontaneous fermentations as wine fermentation starter cultures in the Okanagan Valley wine region in Canada

Winemaking from grape juice is typically carried out using the Saccharomyces cerevisiae (S. cerevisiae) yeast species as a starter culture for ethanolic fermentation. The specific S. cerevisiae strain performing the fermentation plays a key role in shaping the aroma profile of the wine. Commercially available strains of S. cerevisiae improve the reproducibility and predictability of wine by establishing well-controlled fermentations. However, indigenous S. cerevisiae strains may be better acclimated to the conditions of a particular wine producing region and may enhance the sensory properties and characteristic profiles of the wine. This work assesses the oenological performance of S. cerevisiae strains isolated from the Okanagan Valley wine region in Canada in laboratory and pilot-scale fermentations. Six indigenous S. cerevisiae strains isolated from spontaneous fermentations at Okanagan Crush Pad (OCP) winery were selected for this research. Pinot gris and Pinot noir grape juice was used to perform 250 mL lab-scale fermentations carried out at 20 °C and 25 °C, respectively. Primary metabolites were quantified by high pressure liquid chromatography coupled to a refractive index detector (HPLC-RID) and volatile compounds were quantified by solid phase microextraction coupled to gas chromatography and mass spectrometry (SPME-GC/MS). Lab-scale Pinot gris wines produced with OCP indigenous strains had higher concentrations of the ester ethyl butanoate (apple, pineapple aroma) than lab-scale wines fermented with a commercial strain. OCP-088 and OCP-125 strains were selected for OCP winery pilot-scale fermentations in 250 L stainless steel barrels with Pinot gris and Pinot noir juice during the 2022 harvest. Both OCP strains persisted throughout the fermentations. Residual sugars were identified in both wines, primarily consisting of fructose at a range of 16-22 g/L and the alcohol by volume of the finished wine ranged from 10.82-11.58 %. Pilot-scale wines produced with OCP-088 and OCP-125 strains had a similar aroma composition, producing an off-dry wine with a desirable fruity aroma bouquet that had a higher concentration of the ester ethyl decanoate (sweet, fruity aroma) than commercial wines fermented in the same vintage. This study indicates that Okanagan indigenous strains ferment wines with desirable aromatic profiles and may be suitable as starter-cultures for producing wine reflective of the region.