A closure for a beverage container (2), such as a beer bottle, includes a closure plate (10), connected to which is a diaphragm (20), which together with the closure plate defines a gas reservoir (22). A movable portion (24) of flexible material is integrally connected to the diaphragm (22). The upper end of the 10 movable portion, which may be in the form of a tube (24) or pocket (3), is open and communicates with the gas reservoir and the other end is substantially closed and has a gas charge/discharge orifice (28) formed in it. The movable portion is connected to the remainder of the diaphragm by at least one pair of fold lines of opposite sense. When the closure is applied to a container, the gas charge/discharge orifice (28) is above the liquid level. The headspace of the container and the reservoir (22) are filled with pressurised gas and when the pressure is released the pressure differential across the movable portion results in rotation about the fold lines with the result that the movable portion moves away from the closure plate so that the gas charge/discharge orifice is situated beneath the liquid surface and the pressurised gas in the gas reservoir (22) is injected into the liquid in the container.