The present invention provides a process for transforming an alpha acid into an iso-alpha acid, involving contact of the alpha acid with an aqueous solution of a metal ion, comprising the steps of contacting an aqueous solution of the metal ion with a water-immiscible organic solvent solution of the alpha acid under conditions whereunder the alpha acid is dissolved or remains dissolved in said organic solvent and effecting the desired isomerization in the water-immiscible organic solvent, with or without prior separation of said solvent containing said alpha acid from the aqueous phase.Numerous advantages accrue to the employment of this process over prior-art procedures. Humulones are readily isomerized to isohumulones, and hop extracts are readily isomerized to "preisomerized" hop extracts. The products have utility as flavoring additives.