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The stability of bitter substances in beer during the ageing process - HOP SPECIAL - WINNER OF LUDWIG-NARZISS-AWARD 2021
A. Gahr, A. Forster, F. Schüll, S. Faltermaier and F. Kellerer

The changes in hop bitter substances in beer over the course of ageing and the associated decline in sensory quality have been the subject of numerous studies, but none of these have explored if bitter substances react differently during ageing based on whether the hops are added on the hot or on the cold side. To elucidate this a lager beer was brewed with a late aroma hop addition in the brewhouse and additionally dry hopped. Both beers were stored for two years at 4 °C, 22 °C and 30 °C. Overall, ageing the beers at 4 °C resulted in minor changes only. Based on the analysis of the beers aged at 22 °C and 30 °C, the following observations can be drawn: Starting with the cis-iso-α-acids via the bittering units, total iso-α-acids, trans-iso-α-acids and on to the α-acids, the losses of these substances increase significantly. Trans-iso-α-acids are 5 to 8 times more sensitive to degradation than the cis form. The behaviour of co-hulupone was comparatively stable in this regard. A marked difference between the homologs (co-, n- and ad-) of the iso-α-acids could not be found in both beers. However, all of the bitter substances in the dry-hopped beers showed less degradation due to ageing than those in the late-hopped beers. Whether the higher stability of the bitter substances in dry-hopped beer can be attributed to the changes in its composition through the addition of dry hops cannot be clearly established. Additional polyphenols added by dry hopping could potentially provide a "more stable environment" with a higher antioxidative potential. A distinct decrease in xanthohumol was observed; however, it was largely offset by an equivalent increase in isoxanthohumol. Late and dry hopped beers showed no differences with regard to the prenylflavonoids.

Descriptors: beer ageing, hop bitter substances, iso-α-acids, humulinones, hulupones, flavour stability

BrewingScience, 73 (November/December 2020), pp. 149-157