Abstract: A process is described for converting the .alpha.- and .beta.-acids of hops into the iso-.alpha. acids for use as a bitter flavoring principle ingredient for beers. The .alpha.-acids content of the hops is directly isomerized to the iso-.alpha.-acid, the bitter principle ingredient. The .beta. acids in the hops extract is transformed to the .alpha. acid either after a direct separation step before the .alpha.-acid isomerization or the residual .beta.-acids, after the isomerization, are then transformed and the resultant .alpha.-acid is isomerized. The .beta.-acid transformation results from a radiation activation followed by an oxidation step with a per - acid.The isomerization of the .alpha.-acid to the iso-.alpha.-acid is accomplished by reaction with an alkaline earth metal ethoxide preferably the magnesium ethoxide.