A New Parameter for Determination of the Extent of Staling in Beer

The change in hop bitter substances in beer during storage was studied using HPLC. A significant difference was observed in the rates of reduction in isohumulone levels during beer storage. The trans form of n-isohumulone decreased with beer storage time, while the cis form remained unchanged. The trans-cis ratio, based on peak areas, was similar for fresh beers regardless of the beer specification, but it decreased in aged beer, to extents differing between beers. A good correlation between the trans-cis ratio and the stale flavor intensity of the beer was also confirmed, such that the trans-cis ratio reflected the degree of oxidative deterioration of the beer.