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.