Influence of killer strains of Saccharomyces cerevisiae on wine fermentation

The effect of killer strains of Saccharomyces cerevisiae on the growth of s ensitive strains during must fermentation was studied by using a new method to monitor yeast populations. The capability of killer yeast strains to el iminate sensitive strains depends on the initial proportion of killer yeast s, the susceptibility of sensitive strains, and the treatment of the must. In sterile filtered must, an initial proportion of 2-6% of killer yeasts wa s responsible for protracted fermentation and suppression of isogenic sensi tive strains. A more variable initial proportion was needed to get the same effect with non-isogenic strains. The suspended solids that remain in the must after cold-settling decreased killer toxin effect. The addition of ben tonite to the must avoided protracted fermentation and the suppression of s ensitive strains; however, the addition of yeast dietary nutrients with yea st cell walls did not, although it decreased fermentation lag.