Apparatus for concentrating a vapour comprising: an optional vaporizer, a vapour flow conduit； a counter flow conduit； an optional humidity controller； and wherein at least a portion of said vapour flow conduit and said counter-flow conduit define respective opposed sides of a membrane. A plurality of alternating vapour flow conduits and corresponding counter-flow conduits may be present. The alternating vapour flow conduits and counter-flow conduits may for example be in a layered configuration or in a concentric, coaxial tubular arrangement. Also, a method of producing a concentrated active from a solution comprising an active in a solvent and having a first active:solvent ratio, said method comprising the steps of: (1) vaporizing the solution to form a vapour wherein the concentration of active is at about said first ratio, (2) providing a flow of the vapour to a first side of a membrane； and (3) providing an alternate flow of a gas to a second side of the membrane whereby to increase said first active:solvent ratio on the first side to a second active:solvent ratio greater than the first active:solvent ratio.
