Specific impact of nitrogen supplementation on the metabolism of Saccharomyces and hybrids during wine fermentation

Nitrogen is essential for yeast metabolism and is often added to avoid slow or stuck fermentations in the wine industry. This study aimed to investigate the impact of different nitrogen supplementation strategies on the metabolism of various Saccharomyces yeast strains, with a particular focus on their fermentative performance, primary metabolite production, and aromatic profiles, including polyfunctional mercaptans (PFMs) varietal aromas. Two nitrogen supplements, organic (amino acids) and inorganic (NH₄Cl), were evaluated under conditions and addition limits representative of the oenological industry, using Saccharomyces cerevisiae and interspecific hybrid strains (S. cerevisiae x S. uvarum and S. cerevisiae x S. kudriavzevii). The findings of this study indicate that the effect of nitrogen supplementation on yeast fermentation and aroma production is highly strain dependent. While inorganic nitrogen generally improved fermentation kinetics, its influence on metabolite production and aromatic profiles varied across strains. Nitrogen supplementation had minimal impact on ethanol, glycerol, acetic acid, and malic acid metabolism but significantly affected succinic and lactic acid production. Additionally, organic nitrogen supplementation was particularly effective in enhancing polyfunctional mercaptans (PFMs) in specific strains such as S. cerevisiae x S. kudriavzevii hybrid strains. In contrast, inorganic supplementation favoured the production of ethyl esters and medium chain fatty acids. Overall, the study emphasizes the significance of selecting the appropriate type of nitrogen based on the yeast strain and desired wine characteristics. This knowledge can help winemakers optimize fermentation processes to achieve specific sensory profiles, thereby enhancing the aromatic quality of their wines.