Influence of aeration on the physiological activity of flor yeasts

The effect of periodic aeration on the physiological activity of a strain o f Saccharomyces cerevisiae yeast during development of velum (flor) and bio logical aging of Sherry wine of the Fine type was investigated. L-Proline a mino acid was the main nitrogen source for yeasts cells during the biologic al aging, and its exhaustion may be the cause of the production and consump tion of other compounds that are involved in the aroma of wines. Aeration w as found to increase adenylate energy charge, growth, and viability of the yeast cells. Also, it affected the intracellular redox equilibrium and the consumption and production of compounds including acetoin, acetaldehyde, hi gher alcohols, ethanol, glycerol, and acetic acid. Acetaldehyde reached its highest level after the second aeration, which coincided with the exhausti on of the nitrogen source in the medium. The enzyme activity of alcohol deh ydrogenases I and II decreased inmediately after each aeration, subsequentl y increasing once ail of the dissolved oxygen in the wine had been consumed by yeast cells. Aldehyde dehydrogenase activity was detected only after th e first aeration, and it may be related to the production and consumption o f acetic acid in the wine.