RT Journal Article
SR Electronic
T1 Distribution of Yeast Cells, Temperature, and Fermentation By-Products in White Wine Fermentations
JF American Journal of Enology and Viticulture
JO Am J Enol Vitic.
FD American Society for Enology and Viticulture
SP ajev.2019.18092
DO 10.5344/ajev.2019.18092
A1 Mira Schwinn
A1 Dominik Durner
A1 Antonio Delgado
A1 Ulrich Fischer
YR 2019
UL http://www.ajevonline.org/content/early/2019/06/05/ajev.2019.18092.abstract
AB Yeast inoculation from the top of tanks is a usual practice in white wine fermentations. The objective of this study was to examine if inhomogeneities occur in tanks following yeast addition from the top with and without short stirring after inoculation. It was investigated if inhomogeneities affect fermentation kinetics and formation of acetaldehyde, acetic acid and pyruvate in Riesling juices with low turbidity. Samples and temperatures were taken at different tank heights in pilot-scale (105 L) and industrial-scale tanks (2500 and 7000 L) to investigate distributions of temperature, yeast and fermentation products in tanks of different volumes and height-to-diameter ratios. When yeast was not stirred in following inoculation, cell counts were higher in the upper tank section over the first days. Fermentation started earlier at the top of the tank as indicated by a lower specific gravity. From top to bottom, differences of up to 0.040 in specific gravity and up to 8.6°C in temperature were observed. Inhomogeneities lasted four days in 7000 L tanks. Results suggest slow yeast sedimentation and poor mixing in the downwards direction during pre-fermentation. During vigorous fermentation, all parameters were homogenously distributed. Short stirring after yeast inoculation provided uniform conditions during the pre-fermintation phase except for temperature differences which were due to natural stratification. Fermentation duration was shorter when yeast was stirred in. The final pyruvate concentration was significantly lower when the yeast was stirred in, presumably due to better nutrient availability throughout the whole tank, reducing SO2 demand. No differences were observed in acetaldehyde and acetic acid. When the yeast is not stirred in, sampling valves and temperature sensors of tanks do not reflect the whole tank during pre-fermentation which must be considered adverse for process control.