Effects of nutrient supplementation on fermentation kinetics, H2S evolution, and aroma profile in Verdicchio DOC wine production

Different yeast nutrient additions were studied for the 2008 and 2009 vintages of Verdicchio grape juice fermentation. Addition of yeast derivatives at the beginning of fermentation and/or different amounts of diammonium phosphate at various times within the first half of fermentation were examined, with initial yeast assimilable nitrogen concentrations set at 200 mg l-1 and 250 mg l-1. Supplementation with glutathione in combination with this nitrogen addition was also evaluated. Fermentation rates were monitored throughout these fermentations carried out under different nutrient conditions. H2S production during fermentation and synthesis of volatile compounds in the finished wines were quantified; the wines also underwent sensory evaluation. The fermentation kinetics of Saccharomyces cerevisiae were almost exclusively influenced by the inorganic nitrogen supplementation with diammonium phosphate. H2S evolution by S. cerevisiae was more affected by assimilable nitrogen than glutathione. Diammonium phosphate significantly reduced H2S production, with a further reduction in the presence of yeast derivative. This nitrogen supplementation yielded higher concentrations of acetate esters, and in particular of isoamyl acetate (fruity aromas), which positively influences the analytical and aroma profile of wines, and results in a general reduction in 2-phenylethanol production (floral aromas). Overall results (two harvesting times and vintages) indicates that the management with diammonium phosphate and yeast derivative supplementation improves the kinetics of fermentation and provides a good tool to reduce H2S formation and increase the analytical and sensory quality of Verdicchio wine.