A beverage forming system that includes a capsule for containing beverage ingredients and having an outer surface; a capsule-based beverage producing device provided with a member for injecting a liquid under pressure into the capsule, a member for draining a beverage from the capsule, and an enclosing member transferable from an opened state to a defined closed state, in which the enclosing member encloses the outer surface of the capsule; and a sealing member associated with the capsule and which is compressible when engaged by the enclosing member in the closed state, wherein the sealing member is effective to compensate for the clearance between the enclosing member and the capsule which would otherwise exist when the enclosing member is in its defined closed state. Also, a method for producing a beverage using such a system.