Degradation of Iso-α-Acids During Wort Boiling
2010
Kappler, S. | Krahl, M. | Geissinger, C. | Becker, T. | Krottenthaler, M.
A detailed study on the degradation of iso-α-acids was conducted. Because of the complexity of the wort matrix and interfering interactions during real wort boiling, the investigation of degradation kinetics was performed in an aqueous solution. Degradation was investigated as a function of time (0-90 min), temperature (80-110 degrees C), pH value (4-7), original gravity (10-18 degrees P) and ion content of the water (0-500 ppm Ca2+ and Mg2+). After 90 min of boiling, over 20% of the dosed iso-alpha-acids could no longer be detected. A strong dependence of degradation could be shown due to high temperature, low pH, high original gravity and a high Mg2+ content. The cis:trans ratio and co-iso-alpha-acid content did not change significantly. Losses of isohumulones could be lowered by reducing the temperature and original gravity, as well as by heightening the pH value. High amounts of Ca2+ and Mg2+ salts also led to an increase in degradation products. Solutions to decrease degradation and thereby possible improvements in sensory bitter quality are discussed.
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