The relationship between yeast strains of S. cerevisiae sensitive to the killer factor and others producing this factor was studied while using a new methodology to monitor yeast populations. The ability of killer yeasts to eliminate the sensitive yeast depends essentially on the initial proportion of killer yeast in the initial microflora. This effectiveness of the killer yeast depends equally on the sensitive yeast population level and fermentation conditions in the must. In a sterile filtered must, an initial proportion of 2 to 6 pourcentage of killer yeast, in the initial mixture, dominates the fermentation while eliminating isogenic sensitive yeast (same yeast strain as the killer yeast but sensitive). This initial proportion varies and must be increased when the sensitive yeast strain is not isogenic. It was observed that the fermentation conditions had an equal effect on the killer factor activity. In white winemaking, the solid particles remaining in suspension after a cold clarification step had a negative effect on the killer factor activity. The addition of bentonite also had an effect on the suppression of sensitive yeast in the co-fermentation experiences with a mixture of sensitive and killer yeast. On the other hand the addition of complex nutrients (containing yeast hulls) did not have an inhibiting effect on the killer factor activity.

Related sheets: