Role #1: Starmerella bacillaris is a non-Saccharomyces yeast recently proposed for grape fermentation in association with Saccharomyces cerevisiae. Due to its high glycerol and moderate volatile acidity production this yeast can contribute to improving wine quality. Previous research has also demonstrated that S. bacillaris has a lower sugar to alcohol conversion compared to S. cerevisiae, and in addition, it is also fructophillic.
Role #2: Some strains have been demonstrated to exhibit antifungal activity against grey mould on grape, which is caused by Botrytis cinerea.
The simultaneous presence of these traits in S. bacillaris is of great interest. Indeed, this yeast can be potentially used as a biocontrol agent in vineyards. Research on the ability of S. bacillaris to survive or, even to grow on the surface of grapes is a starting point in the evaluation of its potential use in vineyards.
EXPERIMENTAL LAYOUT
Each grape bunch was dipped in a Starmerella bacillaris yeast solution for 2 min and the volume of solution that adhered to the surface was calculated by weighing each bunch before and after dipping. Finally, bunches were divided into groups of five and hung from a thread without touching each other in a closed plastic box at 25 °C for 0 (T0), 24 (T1) and 144 (T6) hours after dipping. At each time point, five bunches were separately crushed in sterilised flasks and kept at 20 °C. Forty-eight hours after grape crushing, S. cerevisiae EC1118 (approximately 106 cells/mL) was inoculated. Five bunches were used as a control; they were immediately crushed after washing and inoculated with S. cerevisiae EC1118. All the flasks were kept at 20 °C until the end of fermentation. The fermentations were considered completed when the sugar residue was lower than 1 g/L.
RESULTS
The preliminary results of this study showed that when applied to the grape surface under laboratory conditions, inoculum sized S. bacillaris with antifungal activity developed and lasted for at least six days in high concentrations. In addition, it positively influenced the fermentation process by producing high concentrations of glycerol. Interestingly, a positive effect on wine quality was also observed when the inoculum size was 10 times higher or lower than the reference concentration.
SIGNIFICANCE OF THE STUDY
When sprayed on the vines in the vineyard and present on the grape skin surface after harvest, S. bacillaris cells can start alcoholic fermentation.
MAIN REFERENCE
Nadai, C., Giacomini, A., & Corich, V. (2021). The addition of wine yeast Starmerella bacillaris to grape skin surface influences must fermentation and glycerol production. OENO One, 55(2), 47–55. https://doi.org/10.20870/oeno-one.2021.55.2.4556
ADDITIONAL REFERENCE
Coetzee, C. (2019). Sequential inoculation of Starmerella bacillaris and Saccharomyces cerevisiae – main effects. WineLand Media, https://www.wineland.co.za/sequential-inoculation-of-starmerella-bacillaris-and-saccharomyces-cerevisiae-main-effects/
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