Alterations of the profiles of iso-alpha-acids during beer ageing, marked instability of trans-iso-alpha-acids and implications for beer bitterness consistency in relation to tetrahydroiso-alpha-acids

Age-induced decomposition of iso-alpha-acids, the main bittering principles of beer, determines the consistence of the beer bitter taste. In this stud y, the profiles of iso-alpha-acids in selected high-quality top-fermented a nd lager beers were monitored by quantitative high-performance liquid chrom atography at various time intervals during ageing. The degradation of the i so-alpha-acids as a function of time is represented by the ratio, in percen tage, of the sum of the concentrations of trans-isocohumulone and trans-iso humulone to the sum of the concentrations of cis-isocohumulone and cis-isoh umulone. This parameter is relevant with respect to the evaluation of bitte rness deterioration in aged beers. Trans-iso-alpha-acids having a shelf hal f-life of less than one year proved to be significantly less stable than ci s-iso-alpha-acids, but it appears feasible to counteract degradation if a s uitable beer matrix is available. The fate of the trans-iso-alpha-acids in particular adversely affects beer bitterness consistency. In addition to us ing hop products containing low amounts of trans-iso-alpha-acids, brewers m ay profit of the remarkable stability of tetrahydroiso-alpha-acids, even on prolonged storage, for the production of consistently bitter beers.