Effects of the Grape Must Lees and Insoluble Materials on the Alcoholic Fermentation Rate and the Production of Acetic Acid, Pyruvic Acid, and Acetaldehyde

The influence of grape must lees from clarification, grape must clarification coadjuvants (bentonite, diatomaceous earth powder, charcoal, cellulose, and gelatin and silica gel), and inert insoluble materials (glass beads, quartz powder, and talc) on fermentation rate and production of acetaldehyde, acetic and pyruvic acids was verified in clarified grape must and in a synthetic nutrient medium (MNS), using a "low acetic acid producer" yeast strain and a "high acetic acid producer" strain. The addition of clarification deposit had the strongest and the most significant effect in both clarified grape must and in MNS. It decreased the acetic and pyruvic acid production, reduced the latent phase, and increased the fermentation rate, particularly in MNS and with the "high acetic acid producer" yeast strain. A low, but significant, effect was verified for diatomaceous earth powder and talc in reducing the acetic and pyruvic acid productions. Gelatin and silica gel caused a stronger release of these acids in the medium. The acetaldehyde production was not significantly influenced by the clarification lees or by the other insoluble materials except by gelatin and silica gel, which caused a small increase in grape must. This occurred with the "high acetic acid producer" yeast strain only. The hypotheses that may explain the results obtained are discussed.