Volatile Composition and Sensory Properties of Shiraz Wines As Affected by Nitrogen Supplementation and Yeast Species: Rationalizing Nitrogen Modulation of Wine Aroma

The effects of yeast assimilable nitrogen (YAN) supplementation on Shiraz volatile composition and sensory properties have been investigated. A low VAN Shiraz must (VAN 100 mg/L) was supplemented with nitrogen in the form of diammonium phosphate (DAP) to a final YAN of either 250 or 400 mg/L. Fermentation was carried out with either Saccharomyces cerevisiae or Saccharomyces bayanus, with maceration on skins. For both yeast strains, high DAP additions increased the ratings of positive sensory attributes such as red fruit and dark fruit and decreased the yeast/cheese, vegetal, and earth/dirty attributes. For the S. cerevisiae yeast moderate DAP addition resulted in higher reduced attribute scores. DAP supplementation had a strong influence on formation of acetates, fatty acid ethyl esters, higher alcohols, hydrogen sulfide, ethyl mercaptan, methyl mercaptan, DMS, and DES. Partial least-squares regression analysis of chemical and sensory data indicated that esters, sulfides, and mercaptans were associated with fruit-related descriptors, whereas hydrogen sulfide was associated with the reduced attribute. Nitrogen-related variations in the concentration of other yeast metabolites such as ethanol and 2- and 3-methylbutanoic acids also affected perceived fruitiness. Depending on yeast species DAP supplementation to a low nitrogen must can result in increased reduction off-odor.