Velum Formation by Flor Yeasts Isolated From Sherry Wine

S. cerevisiae strains which form velum (flor) on the surface of sherry wine during the aging process can grow and survive in the presence of high concentrations of ethanol (over 15% v/v). This is due to an adaptive mechanism expressed by flor yeasts that consists of changes in their size, shape and cell hydrophobicity which allow the population to float, growing on the surface of sherry wine. Hydrophobicity makes cells aggregate and these aggregates retain gas bubbles originated in the respiration process. As a consequence, the population of flor yeasts becomes less dense than the wine. The addition of ergosterol and/or oleic acid has no effect, indicating that the process might depend on the synthesis of hydrophobic proteins rather than lipids. Incubation with proteases breaks up the velum and produces free cells, thus supporting this suggestion. The rate of flor formation varies with the strain, appearing sooner in more ethanol-sensitive strains.