Christian Vogelei,* Philipp Franke, Matthias Kowalcyzk, Roxana Tudorie,  Christian von Wallbrunn, Dominik Durner, and Maren Scharfenberger-Schmeer *Weincampus Neustadt, Breitenweg 71, 67435 Neustadt, Germany (christian.vogelei@dlr.rlp.de)

High-gravity grape musts are the basis of premium and sweet wines. Their sugar content can reach up to 400 g/L. Those high sugar amounts may increase osmotic stress for the wine yeast Saccharomyces cerevisiae and increase amounts of undesired secondary metabolites such as acetic acid and acetaldehyde, which may damage the quality of the final product. We investigated the metabolic and transcriptional response of S. cerevisiae to the high sugar content of high-gravity grape musts. The stress response is divided into an initial stress adaption to the high-sugar environment, followed by biosynthesis and release of several secondary metabolites from the glycolytic pathway. To reduce the stressful conditions for the wine yeast and the biosynthesis of undesired byproducts, we applied fed-batch technology to ferment the high-gravity grape musts. We investigated the synthesis and release of the most important fermentation byproducts and the transcriptional response of the wine yeast during fed-batch fermentations in comparison to regular batch fermentations. Under fed-batch conditions, the S. cerevisiae can ferment greater amounts of sugar and releases smaller amounts of problematic secondary metabolites such as acetic acid and acetaldehyde. We used gene expression analyses to investigate expression of marker genes related to osmotic stress response, such as stress-inducible acetic acid biosynthesis. In addition, we monitored the regulation of key genes in certain parts of the glycolytic pathway during the fermentation process. Our data show good correlation of transcriptional and metabolic activity and give insight into the molecular processes during fed-batch and batch fermentation processes of high-gravity musts.

Funding Support: FHproUnt (lead partner Jülich), Federal Ministry of Education and Research (Federal Republic of Germany), Federal Institute of Viticulture and Horticulture Neustadt, Germany (DLR Rheinpfalz, Neustadt), University of Applied Sciences Kaiserslautern, Germany, University Geisenheim