The future of DMS precursors during alcoholic fermentation: impact of yeast assimilable nitrogen levels on the contents of DMSp in young wines

Abstract

Some red wines develop a “bouquet” during ageing. This complex aroma is linked to quality by wine tasters1. The presence of dimethylsulfide (DMS) in those wines is implicated in the expression of “bouquet typicity”2. DMS is a result of the hydrolysis of its precursors. Several molecules, including S-methylmethionine, could constitute the precursors of DMS3. DMS can be liberated by alkaline hydrolysis and quantified by SPME-GC-MS4. The releasable DMS is designated by “DMSp”. The DMSp levels in grapes are 20 to 30 times higher than those observed in young wines5. Our question is : “What happens during the stages of fermentation?”First, DMSp levels were studied during a small-scale winemaking process and were measured in musts, in wine after alcoholic fermentation (AF) and after malolactic fermentation (MLF). Then, to understand the mechanism of the DMSp degradation, synthetic must was used with various levels of YAN and different pools of inorganic and organic nitrogen such as amino acids. Synthetic musts were supplemented by one of the known DMS precursor (S-methylmethionine), inoculated with S. cerevisiae and the fermentations were monitored by evaluating CO2 evolution.During AF, around 90% of DMSp is degraded by the action of yeast. The MLF consumed a little DMSp but it is negligible compared to AF. The link between DMSp and nitrogen would generate a variable consumption of DMSp during AF. Then, DMSp is consumed at the beginning of alcoholic fermentation during the yeast growth step and the level of consumption depends of the constitution of YAN. The several pools of nitrogen substances of YAN tested shows various results about the consumption or conservation of DMSp during AF.Finally, the assays in laboratory to try to control DMSp levels in young wine will help the winemakers to keep the ageing potential of red wine and maintain a high quality of wine.