EFFECTS OF ETHANOL AND TEMPERATURE ON THE BIOLOGICAL AGING OF SHERRY WINES

The film formed by flor yeasts on the surface of ''fino'' sherry wines was studied over a period of two years. The periodic analyses of this film indicated that temperature and ethanol strongly influenced its s tate. When a critical value established at 22.5 degrees C and 15% etha nol was exceeded, the yeast layer becomes deteriorated. The deteriorat ion of the yeast film correlated with a significant increase in the pr oportion of respiratory-deficient (rho(-)) mutants. These mutants lack the ability to form a velum, indicating that aerobic metabolism is re quired for flor yeasts to develop this characteristic. In addition, it suggests that the appearance of such mutants by elevated temperatures may contribute to the deterioration of the yeast layer. Once formed, the yeast film kept stable after the induction of 100% rho(-) cells wi th ethidium bromide, indicating that the velum is a long-life biologic al structure at temperature lower than 20 degrees C. This result also suggests that the induction of rho mutants by ethanol and elevated tem perature is not the only mechanism leading to velum deterioration by e thanol and temperature on sherry wines.