Assessment of changes in hop resins and polyphenols during long-term storage

Changes in the content and composition of hop secondary metabolites during storage are reflected in beer quality and in the economics of beer production. A 12-month storage experiment with T90 pellets of four hop varieties showed different dynamics of hop aging in relation to both storage conditions and hop variety. Negligible effects on the α- and β-acids were detected during storage without air access at +2°C. Storage at +20°C resulted in a final loss of 20–25% α-acids, but the content of β-acids did not change significantly. Large decreases in α-acids (64–88%) and in β-acids (51–83%) were found in hops stored with access to air at +20°C. The rate of decline accelerated markedly after 6 months of storage. In terms of hop resin changes, Premiant and Sládek were the most and the least stable varieties, respectively. After 12 months, the content of the total polyphenols and flavonoids decreased by 30–40% and by 20–30%, respectively, irrespective of storage conditions. The rate of decline accelerated strongly after 6 months. The DPPH (1,1-diphenyl-2-picrylhydrazyl) antiradical potential decrease was significant only in hops stored under aerobic conditions. The depletion was 9–25% after 1 year; Saaz was the most stable variety. Copyright © 2012 The Institute of Brewing & Distilling