A continuous process for treating a raw ligno-cellulosic biomass stream, comprising water insoluble contaminants and a ligno-cellulosic biomass comprised of a ligno-cellulosic component, non-ligno-cellulosic water soluble compounds and non-ligno-cellulosic water insoluble compounds, said process comprising the steps of: a. introducing the raw ligno-cellulosic biomass stream into an extraction vessel containing an extraction solution comprising water and water soluble species and having a first electrical conductivity, wherein at least a portion of the extraction solution derives from the extraction of a portion of ligno-cellulosic biomass previously treated and contains water soluble species derived from the non-ligno-cellulosic water soluble compounds of the previously treated ligno-cellulosic biomass; b. releasing into the extraction solution additional water soluble species derived from the non-ligno-cellulosic water soluble compounds of the ligno-cellulosic biomass, to produce a soaked ligno-cellulosic biomass stream; c. removing the soaked ligno-cellulosic biomass stream from the extraction solution; d. optionally rinsing the soaked ligno-cellulosic biomass stream with a rinse solution stream comprising water; e. separating the soaked ligno-cellulosic biomass stream into at least a ligno-cellulosic biomass stream and a soaking liquid having a second electrical conductivity and comprising water and water soluble species derived from the non-ligno-cellulosic water soluble compounds of the ligno-cellulosic biomass; characterized by the step of f. diluting the extraction solution with at least a dilution stream comprising water, wherein the flow of the dilution stream and/or the flow of the optional rinse solution stream are regulated to control at least one of the first electrical conductivity and the second electrical conductivity to a target value which is in the range of 0.1 S/m to 5 S/m. a. introducing the raw ligno-cellulosic biomass stream into an extraction vessel containing an extraction solution comprising water and water soluble species and having a first electrical conductivity, wherein at least a portion of the extraction solution derives from the extraction of a portion of ligno-cellulosic biomass previously treated and contains water soluble species derived from the non-ligno-cellulosic water soluble compounds of the previously treated ligno-cellulosic biomass; b. releasing into the extraction solution additional water soluble species derived from the non-ligno-cellulosic water soluble compounds of the ligno-cellulosic biomass, to produce a soaked ligno-cellulosic biomass stream; c. removing the soaked ligno-cellulosic biomass stream from the extraction solution; d. optionally rinsing the soaked ligno-cellulosic biomass stream with a rinse solution stream comprising water; e. separating the soaked ligno-cellulosic biomass stream into at least a ligno-cellulosic biomass stream and a soaking liquid having a second electrical conductivity and comprising water and water soluble species derived from the non-ligno-cellulosic water soluble compounds of the ligno-cellulosic biomass; characterized by the step of f. diluting the extraction solution with at least a dilution stream comprising water, wherein the flow of the dilution stream and/or the flow of the optional rinse solution stream are regulated to control at least one of the first electrical conductivity and the second electrical conductivity to a target value which is in the range of 0.1 S/m to 5 S/m.