Abstract—The thermal degradation of iso-alpha-acids was investigated at four pH levels between 4.5 and 6.5 at different boiling temperatures (90-130 °C) during the wort boiling time (0-360 min). The free energy of activation and the reaction rate constant (k) of the degradation of iso-alpha-acids were calculated. Raising pH value from 4.5 to 5.5 and from 5.5 to 6.5 decreased the reaction energy about 20 kJ/mol. The relative proportion of isocohumulone stays almost constant. We developed a kinetic model for the irreversible consecutive reation; iso-alpha-acids are isomerized form of alpha-acids by the application of heat in solution and at the same time iso-alpha-acids are degraded to humulinic acids and other compounds. This kinetic model is useful to calculate time to added hops into boiling kettle.

Index Terms—Activation energy, alpha-acids, degradation, iso-alpha-acids, kinetics, pH value.

The authors are with the Technical University Munich, Chair of Brewing and Beverage Technology, 85354 Freising Germany (e-mail: yarong.huang@wzw.tum.de, johannes.tippmann@wzw.tum.de, tb@wzw.tum.de).

Cite: Yarong Huang, Johannes Tippmann, and Thomas Becker, "Kinetic Modeling of Hop Acids during Wort Boiling," International Journal of Bioscience, Biochemistry and Bioinformatics vol. 3, no. 1, pp. 47-52, 2013.