Approaches to limit S-off-flavors during white wine fermentation with specific emphasis on yeast nitrogen nutrition

Low molecular weight volatile sulfur compounds are associated with the “reductive” off flavor of wines. The formation of 15 sulfide off-flavor compounds has been monitored with a novel HS-SPME GC-PFPD method and SIDA quantification during white wine fermentation. Since it is known that glutathione (GSH) might buffer nitrogen stress of the yeast but can also lead to an increase of S-off-flavors, the effect of GSH addition was investigated. Fermentations were carried out in triplicate with Riesling musts showing low NOPA concentrations whereby we evaluated the effect of diammonium hydrogen phosphate (DAHP), pantothenic acid, inactive dry yeast based nutrient (IDY) and must oxidation. It could be shown that only the addition of 0.6 g/L IDY increased fermentation speed and completed fermentations. The addition of IDY as well as GSH lead to a significant increase in H2S formation. Total yeast cells were increased by must oxidation thus leading to faster fermentation whereby no significant difference in S-off-flavors could be observed. The addition of GSH did not affect yeast viability but increased significantly the negative effect of IDY addition regardless the S-off-flavor investigated. In all fermentations the use of DAHP reduced significantly S-off-flavor formation and could completely prevent both S-Methyl thioacetate and S-Ethyl thioacetate development. Under nitrogen deficient conditions, GSH can be used in white wine making when combined with DAHP