Impact of Mashing-Off Temperature and Alternative Kettle-Hopping Regimes on Hop α-Acids Utilization upon Wort Boiling

In this study, the influence of the mashing-off temperature (78 versus 95°C) on α-acids behavior and isomerization during wort boiling at the 10-L scale was investigated. In addition, various kettle-hopping regimes were applied to determine their possible impact on the isomerization of α-acids into iso-α-acids. As determined by quantitative HPLC as a function of wort-boiling time, mashing-off at 95°C always resulted in significantly higher hop α-acids utilization at the end of wort boiling (approx. 58%) compared with conventional mashing-off at 78°C (approx. 42%). Moreover, with mashing-off at 95°C, iso-α-acid profiles obtained at the end of wort boiling were potentially favorable in view of a finer, less lingering beer bitterness (relatively less isocohumulone) and prolonged bitterness stability upon aging (proportionally less trans-isomers). In regard to alternative hopping regimes, dosed addition of hop material as a function of wort boiling time resulted in similar α-acids utilizations compared with full hopping at the onset of the boil. Our results point to the potential of alternative ways of kettle hopping, in particular when mashing-off at 95°C, for more economic hopping combined with enhanced bitterness quality and stability.