A closure device for use with a container having a main liquid compartment and an opening with a container neck , the closure device comprising: a spout cap member having a top wall with a spout aperture , a side wall extending below the top wall and adapted to be secured to the opening of the container , and a plug support structure extending from the top wall inside the side wall , a fluid chamber movably held within the spout cap member and having a bottom aperture , the fluid chamber containing an additive liquid and a pressurised propellant, a plug member fixed to the plug support structure and sealingly engageable in the bottom aperture of the fluid chamber , and a spout cover adapted to removably cover the spout aperture , wherein the spout cover includes a strut extending through the spout aperture to an abutment surface on the fluid chamber , wherein the fluid chamber is adapted to move relative to the spout cap member between: a first armed position of the closure device , in which the plug member seals the bottom aperture closed, and the spout cover is engaged with the spout cap member , and the pressurised propellant urges the abutment surface on the fluid chamber against the strut of the spout cover , and a second firing position, in which the spout cover is disengaged from the spout cap member , and the pressurised propellant urges the fluid chamber upwards relative to the plug member , so that the plug member no longer seals the bottom aperture closed. a spout cap member having a top wall with a spout aperture , a side wall extending below the top wall and adapted to be secured to the opening of the container , and a plug support structure extending from the top wall inside the side wall , a fluid chamber movably held within the spout cap member and having a bottom aperture , the fluid chamber containing an additive liquid and a pressurised propellant, a plug member fixed to the plug support structure and sealingly engageable in the bottom aperture of the fluid chamber , and a spout cover adapted to removably cover the spout aperture , wherein the spout cover includes a strut extending through the spout aperture to an abutment surface on the fluid chamber , wherein the fluid chamber is adapted to move relative to the spout cap member between: a first armed position of the closure device , in which the plug member seals the bottom aperture closed, and the spout cover is engaged with the spout cap member , and the pressurised propellant urges the abutment surface on the fluid chamber against the strut of the spout cover , and a second firing position, in which the spout cover is disengaged from the spout cap member , and the pressurised propellant urges the fluid chamber upwards relative to the plug member , so that the plug member no longer seals the bottom aperture closed. a first armed position of the closure device , in which the plug member seals the bottom aperture closed, and the spout cover is engaged with the spout cap member , and the pressurised propellant urges the abutment surface on the fluid chamber against the strut of the spout cover , and a second firing position, in which the spout cover is disengaged from the spout cap member , and the pressurised propellant urges the fluid chamber upwards relative to the plug member , so that the plug member no longer seals the bottom aperture closed. <EOS>