The method of pH controlling during electrolytic fermentation processes of the organic substrates includes placing the biological and chemical reagents in a fermentation tank, placing the electrodes powered by the direct current in the fermentation tank chambers, switching on the constant voltage initiating electrolytic processes with a value from 0.1 to 50 V, generating H+ or OH− ions around the electrodes, reading the data from the glass electrode, changing the power parameters of electrodes, depending on the set pH value of the reaction medium, and starting a pump metering the liquid from the auxiliary chamber into the fermentation tank chamber through a dispensing connector. The object of the invention is also the reactor for carrying out this method.