Pascal Wegmann-Herr,* Sebastian Ullrich, Johanna Kost, Parissa Paydar, and Dominik Durner
*Institute for Viticulture and Enology (DLR-Rheinpfalz), Breitenweg 71, 67435 Neustadt, Germany (pascal.wegmann-herr@dlr.rlp.de)

Low molecular weight volatile sulfur compounds are associated with reductive off‑flavor in wines. Their characteristic odors range from rotten egg to rubber at very low concentrations. The formation of 15 sulfide off-flavor compounds during white wine fermentation was monitored using a novel HS-SPME GC-PFPD method and SIDA quantification. Total yeast population and yeast viability were determined by flow cytometry. Since it is known that glutathione can buffer nitrogen stress in yeast, but can also lead to an increase of S-off-flavors, the effect of GSH addition was investigated. Fermentations with Riesling musts showing low NOPA concentrations were carried out in triplicate, whereby we, first, evaluated the effect of diammonium hydrogen phosphate (DAHP), pantothenic acid, or a yeast autolysates-based nutrient (IDY). It could be shown that only the addition of 0.6 g/L IDY could increase fermentation speed and complete fermentations. The addition of IDY and GSH led to a significant increase H2S formation, the lowest off-flavor concentrations were achieved with DAHP addition, although no S-methyl thioacetate was formed. Second, we investigated the effect of must oxidation, again under different N-nutrition regimes. Total yeast cells and yeast viability increased with must oxidation, leading to faster fermentation with no significant difference in S-off-flavors. The addition of IDY improved yeast viability independently of must treatment, with significant increase in H2S. The addition of GSH (50 mg/L) did not affect yeast viability, but increased significantly the negative effect of IDY addition regardless of the S off-flavor investigated. In all fermentations, the use of DHAP significantly reduced S off-flavor formation and completely prevented both S-methyl thioacetate and S-ethyl thioacetate development over the whole fermentation process. Under nitrogen deficient conditions, GSH can be used in white wine making when combined with DHAP.

Funding Support: Acknowledgment of funding sources: This IGF Project (AIF 28645N) of the FEI is supported via AiF within the program for promoting the Industrial Collective Research (IGF) of the German Ministry of Economics and Energy (BMWi)