Killer Yeasts - Cause of Stuck Fermentations in a Wine Cellar

Abstract

Sluggish fermentations in five fermenters in a wine cellar were investigated. Methylene blue-stains of yeast suspen-sions revealed that approximately 90% of the total yeast population in each of the fermenters were dead. The viable cells in each fermenter were killer yeasts. Polyacrylamide gel electrophoresis of total soluble cell proteins showed that the same killer yeast occurred in each of the five fermenters. The effect of killer yeast on viability and fermentation activity of the wine yeast was studied in an enriched grape juice medium at 20°C and 30°C. Death rate of the wine yeast was considerably higher in the presence of the killer yeast and fermentations were retarded at both temperatures. The killer yeast induced flocculation of the non-flocculent wine yeast. ..., Protracted or stuck fermentations cause serious problems in the wine industry. The phenomenon leads to longer fermentation times and high residual fermenta-ble sugars in dry wines. These factors and the inferior quality of the final product result in financial losses to wineries.