Influencing Factors on Hop Isomerization Beyond the Conventional Range

Abstract

The hop isomerization reaction during the brewing process is interfered by many factors such as wort composition and time resulting in significant bitter substance losses. A novel mash filtration system provides new possibilities, as four wort flows (instead of one) are separated in parallel and thus different wort characteristics are available for enhancing the hop isomerization rate. A laboratory-scale screening experiment was performed to investigate the different effects of the wort parameters beyond the conventional brewhouse range. Based on previous industrial field trials, the boundary parameters (minimum and maximum) of the laboratory-scale wort fractions, corresponding to filter modules 1 and 4, were adjusted accordingly to the pH value (pH 5.6 or 7.0) and original gravity (17.0 or 2.0°P). The parameters boiling time and dosing quantity of α-acids were adapted to conventional brewhouse standards as well as to the novel system. Additionally, the influence of magnesium (0.0 or 40.0 mg/L) dosed to the wort on the isomerization reaction was tested. The results showed that the boiling time at a pH value of 5.6 had more influence on the inversion to iso-α-acids than with a wort pH of 7.0. Even with a high original gravity of 17.0°P, an extension of the boiling time showed no significant effect on the isomerization rate.