| Stuck and sluggish wine fermentations, as well as excessive reduced sulfur character, present economic hardships in wine production. Chief causes of problem fermentations are low concentrations of yeast assimilable nitrogen (YAN) in grape musts, however vitamin status can also affect fermentations. While the effects of individual nutrients in grape must on yeast have been studied, interactions between nutrients have not. In particular, the vitamins biotin and pantothenic acid are required by wine yeast in the metabolisms of nitrogen, lipids, and sulfur compounds. Interactions between these nutrients and YAN may therefore affect growth, fermentation rate, and production of volatile compounds either important or deleterious to wine quality.; Factorial experiments were conducted using synthetic grape juice media containing either 0, 1, or 10 mug/L biotin and 60 or 250 mg/L YAN. These media were fermented using different wine strains of Saccharomyces cerevisiae or S. bayanus. Both yeasts demonstrated a requirement for biotin for growth and fermentation. While YAN concentration affected maximum fermentation rates, YAN x biotin interactions reduced overall fermentation time at higher YAN levels and influenced the production of H 2S and higher alcohols.; Further studies investigated interactions of YAN, biotin, and pantothenic acid. Factorial studies used synthetic grape must containing either 0.5 or 10 mug/L biotin, 50 or 250 mug/L pantothenic acid, and 60 or 250 mg/L YAN. Significant three-way nutrient interactions were limited. Fermentation rates were primarily influenced by YAN, while YAN x pantothenic acid interactions affected the synthesis of most volatile compounds. The highest levels of H 2S occurred in fermentations with high YAN and low pantothenic acid, but high YAN and high pantothenic acid increased medium chain fatty acid and ester production. Higher alcohols production showed complex responses to nutrient concentrations. Biotin concentration was a minor influence in volatile production.; Results of these studies demonstrated YAN as a dominant factor in fermentative behavior of wine yeast, however interactions with pantothenic acid and biotin can affect yeast performance. The outcome of such studies will assist winemakers in formulating decisions on yeast strains selection, fermentation conditions, and use of nutrient additions in wine production. |
