Factors affecting acetic acid production by yeasts in strongly clarified grape musts.

High acetate content in a wine, after strong clarification of the must, is due to depletion in the yeast cells of important metabolites (normally present in non-clarified musts) such as metals, amino acids, polyphenolic compounds and unsaturated fatty acids. These substances were added separately to a synthetic medium, comparable in composition to the clarified must, which was then inoculated with a high acetate producer strain. No effects were observed after the addition of various metals and amino acids. The addition of unsaturated fatty acids (Tween 80) caused a significant (p = 0.01) decrease in acetate content. Similar results have been obtained in the presence of polyphenols (catechins and anthocyans): their mechanism of action is probably due to direct inhibition of the enzyme aldehyde dehydrogenase. Control experiments were performed with a low acetate producer strain, and a reduction in acetate content was detected. No differences in the glyceropyruvic metabolism of the two strains was evident.