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VIII-22
Evaluation of Oxygen Requirement of Bottom and Lager Yeast Strains by Preoxygenation
Sofie Depraetere, Katholieke Universiteit, Leuven, Belgium
Coauthors: J. Winderickx and F. R. Delvaux
An adequate cellular oxygen supply is critical for yeast growth and its fermentation performance, since oxygen is a necessary building block for the biosynthesis of essential membrane lipids. Traditionally, the cold wort is aerated before pitching. However, this technique has several drawbacks such as inconsistent fermentations and the oxidation of wort constituents, resulting in undesirable color and flavor changes. In order to avoid these shortcomings, yeast can be oxygenated (= preoxygenation) before its use in fermentation. The goals of this research were to gain insight in the oxygen requirement of different yeast strains during preoxygenation and to determine the physiological state of the yeast during preoxygenation and fermentation. Bottom-fermenting as well as top-fermenting yeast strains were evaluated for their preoxygenation ability. Yeast strains were preoxygenated in a membrane loop reactor and yeast characteristics were determined during preoxygenation and fermentation. Oxygen requirements as well as yeast vitality were shown to be yeast strain dependent. Furthermore, knowledge for application of the preoxygenation technique on an industrial scale has been established.
Sofie Depraetere started her studies of applied biological sciences at the KU Leuven in 1996, where she obtained her M.Sc. degree (2001) in bioengineering, majoring in food technology. She is currntly working as a Ph.D. student with an IWT grant in the Department of Food and Microbial Technology at the same university. In collaboration with the Centre for Malting and Brewing Science, she is carrying out a research project on pre-oxygenation of bottom- as well as top-fermenting yeast strains.
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