Winter-Type Gushing Is Induced by Interactions Between Malt Husk-Derived Peptides and Hop-Derived Catechins

Winter-type gushing is a beer overfoaming phenomenon that develops gradually during storage and is strongly influenced by storage history. In this study, malt-derived factors contributing to winter-type gushing were investigated with respect to their physicochemical characteristics and contribution to gushing development. Beers brewed exclusively from the endosperm fraction of malt did not exhibit gushing, whereas reproducible gushing occurred when malt husk fractions were included, indicating that gushing-inducing components originate from minor constituents of the husk. Fractionation analyses localized gushing activity to moderately polar husk-derived fractions and demonstrated that the active components were proteinaceous, most likely low-molecular-weight peptide fragments (≤3 kDa) present in beer. Gushing occurred only in the presence of malt-derived fractions; hop-derived catechin fractions alone did not induce overfoaming, but markedly enhanced gushing intensity when combined with malt-derived components. The dependence of gushing behavior on storage conditions and sample orientation indicates the involvement of physicochemical interactions rather than purely compositional effects. We propose that unstable aggregates formed from malt- and hop-derived components orient at the gas–liquid interface may reduce CO2 dissolution and prolong bubble lifetime, thereby inducing gushing. This study distinguishes essential malt-derived inducers from hop-derived components that enhance gushing.