(57) An improved method of reducing the nitrate, nitrite and ammonium compound content of an aqueous tobacco extract employing microorganisms is described. The nitrates, nitrites and ammonium compounds are eliminated on a continuous basis via an aerobic assimilatory metabolic pathway by introducing aqueous tobacco extract and necessary additives into a work mixture, containing suitable microorganisms, at a dilution rate which does not exceed the growth rate of the microorganisms while withdrawing a portion of the work mixture at a rate such that the volume of the work mixture remains contant. Optionally the biomass may be removed from the withdrawn mixture.