Viruses of Wine-Associated Yeasts and Bacteria

Abstract

Stuck and sluggish fermentations are still a major problem for winemakers. While stuck fermentations can usually be characterized by high residual sugar contents at the end of the alcoholic fermentation, sluggish fermentations are accompanied by a low rate of sugar utilization. In both scenarios, malfermentations can be caused by a variety of factors, most of which lead to a decrease in the metabolism of the fermenting yeast strain, associated by a decrease in biomass production, cell viability, and/or fermentation rate (Bisson 1999). One such factor potentially causing a variety of oenological problems during wine fermentation is the production of toxic proteins, so-called killer toxins, by certain killer yeasts. Soon after the discovery of toxin-secreting killer strains in the wine yeast S. cerevisiae (Bevan and Makower 1963), it became evident that killer yeasts and killer toxins can cause severe stuck fermentations, particularly under conditions when yeast starter cultures become suppressed by wild-type killer strains present on the grapes (Bussey 1981; Young 1987; Heard and Fleet 1987; Vagnoli et al. 1993; Perez et al. 2001; Medina et al. 1997; Santos et al. 2011; de Ullivarri et al. 2014).