Urea Excretion and Uptake by Wine Yeasts as Affected by Various Factors

¹ Dept. of Viticulture and Enology, University of California, Davis, CA 95616-8749.

Eight yeast strains were studied for their urea excretion and uptake during fermentation in a Thompson Seedless grape juice fortified with arginine. Montrachet, Lalvin K-2, and Steinberg yeast were shown to excrete more urea than the other five strains. Prise de Mousse, EC-1118, SB-1, and Epernay 2 yeast gave low amount of urea in the medium. Pasteur yeast excreted intermediate amount of urea. No urea was detected in the medium fermented by Lalvin 71B yeast. The effect of ethanol was examined for Montrachet, EC-1118, and Prise de Mousse. The results indicated that ethanol inhibited yeast growth and arginine uptake, thus reducing urea formation and excretion. The influences of ammonia and individual amino acids (glutamine, alanine, threonine, and serine) were also studied at two arginine concentrations using a nitrogen-deficient Sauvignon blanc grape juice fermented by Montrachet yeast strain. Ammonia and glutamine showed an obvious inhibition on urea re-absorption at two arginine concentrations. Various concentrations of threonine, alanine, and serine had little effect on urea excretion and re-utilization. More urea was excreted and less reabsorbed with higher amounts of arginine added to the grape juice.

Key words: yeast strains, urea, amino acids

Submitted on January 23, 1992

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