Mira Schwinn,* Michael Wacker, Alexander Andre, Dominik Durner, Antonio Delgado, and Ulrich Fischer
*Institute for Viticulture and Oenology, DLR Rheinpfalz, Breitenweg 71, Neustadt an der Weinstraße, Germany (mira.schwinn@dlr.rlp.de)

To ensure high quality, cooling is required during white wine fermentation. However, temperature control is the main contributor to energy demand in wineries. During fermentation, various factors influence the required heat dissipation through the cooling system. The objective of the presented work was to investigate the required heat dissipation and related energy-saving potentials for different temperature managements (14 or 19°C), yeast strains, and tank sizes (110, 1200 or 2500 L). The obtained energy savings are discussed with regard to yeast growth, release of fermentation by-products, and formation of volatile compounds. Heat dissipated by the coolant was determined with an ultrasonic flow meter coupled with probes monitoring temperature differences of the forward and return flows. High energy-saving potentials were revealed for different temperature managements and yeast strains. Depending on tank size, 65 to 90% less heat had to be dissipated to reach the same sugar level when using a temperature regime of 19°C instead of 14°C. For two different yeast strains, there were differences of 20 to 30% in dissipated heat observed in tank sizes of 1200 L and 110 L. Total yeast count and viability investigated by flow cytometry showed faster growth and faster declines in viability at higher temperature. There were also differences in the growth rate and viability between the investigated yeast strains. Analysis of yeast by-products by enzymatic tests showed that concentrations of acetaldehyde tended to be lower at higher temperatures, while acetic acid concentrations were higher. Volatile compounds were quantified via HS-SPME-GC-MS. Differences after fermentation were more pronounced between different yeast strains than for the temperature managements. The results provide valuable experimental data on heat dissipation during fermentation and related energy-saving potentials, including their effect on essential wine quality indicators.

Funding Support: Research Association of the German Food Industry