There is provided a process for modifying a first organic composition comprising (i) at least one first solvent, (ii) at least one solute, and (iii) optionally, at least one second solvent to produce a modified organic composition in which the concentration of the at least one first solvent is reduced and the concentration of the at least one second solvent is increased, comprising the steps of: (a) providing a selectively permeable membrane having a first surface and a second surface; (b) transferring a portion of the first solvent and optionally a portion of the solute from the first surface to the second surface across the membrane by contacting the first organic composition with the first surface, wherein the pressure at the first surface is greater than the pressure at the second surface, and wherein the membrane is a selectively permeable membrane such that the membrane rejection (R) of the solute is greater than 0%; (c) adding a portion of the second solvent to the organic composition retained at the first surface of the membrane.