A vented keg closure (1) for use with a keg (30) that contains a fermenting beverage, with the closure (1) comprising a filter member (41) disposed within an airway of the closure (1) that communicates between an internal headspace (36) of the keg (30) and an environment external to the keg (30). The closure (1) has a first configuration wherein the filter member (41) is located at a first position at which it filters gas flowing through the airway. The closure (1) also has a second configuration wherein the filter member (41) is located at a second position at which gas flow through the airway can be increased by at least partially bypassing the filter (41). The extent of movement between the first and second configurations is controlled by the gas pressure difference across the airway.