Flocculating ability in yeasts of the genusSaccharomyceswhich cause the spontaneous fermentation of grape musts is not rare. About 6.8% of isolates are flocculent. The strains show a different degree of flocculation and also variable developmental behaviour. The genetic analysis, carried out immediately after strain isolation and again after 3 years, shows that only flocculating homozygote strains ensure the stability of the flocculation character over time. Flocculation of some strains shows a degree of instability in the expression of the character which is typical of cytoplasmic inheritance.