Quality control of beer hopped with reduced isomerised products

The traditional method for measuring bitterness in beer by UV absorbance (ASBC 9.6) remains a viable quality control method for normally hopped beer. However, after reduction of isoalpha acids specific absorptivity of active components change and HPLC analysis shows to be a reliable method for quality control of these materials. This work is intended to adapt mathematically the ASBC (American Society of Brewing Chemist) spectrophotometrical method and to evaluate an HPLC method to control the composition of different commercial reduced isomerised products added to unhopped wort and partially kettle hopped beer. The results we obtained showed that the HPLC method is reliable for quality control of reduced isomerised products and that the traditional spectrophotometrical method is viable for quality control of beer, also using reduced isomerised products as far as an adequate factor is used.