AMINO-ACID UTILIZATION AND UREA FORMATION DURING VINIFICATION FERMENTATIONS

The pattern of amino acid utilization was examined in two commercial yeast strains, Montrachet (UCD 522) and Prise de Mousse (Red Star, Universal Foods Corporation) in two grape juices, a pink juice concentrate obtained from the E. & J. Gallo Winery and a Sauvignon blanc juice much less rich in nitrogen. Utilization of nitrogen-containing compounds was markedly similar in these two yeast strains. Prise de Mousse consistently displayed faster fermentation rates and time to dryness, which was particularly striking in the Sauvignon blanc juice which had a much lower total nitrogen content. The release and reutilization of urea was monitored for both strains. Higher medium levels of urea were observed with Montrachet as compared to Prise de Mousse, but levels were similar following greatly extended (eight months) lees contact. Both yeasts displayed significant intracellular levels of urea during the course of fermentation, but the urea remained largely intracellular in Prise de Mousse throughout, while in Montrachet urea was released to the surrounding medium.