The present invention relates to a method of introducing nitrogen into a beverage container. The beverage container (10) includes a cylindrical neck part (16) having a circumferential rim (18) defining an opening (20). The cylindrical neck part includes an outer circumferential flange (22) encircling the cylindrical neck part. A connecting element (36) having a circular closure plate (64) and a cylindrical housing (54) having a set of inwardly oriented locking parts (56) is positioned such that the cylindrical housing is at least partially covering the cylindrical neck part and a fluid path (58) is defined between the connecting element and the cylindrical neck part. A collar (42, 44) having a gas inlet (48) is placed about the cylindrical neck part and gas is injected into the beverage container via the gas inlet. Finally, the connecting element is moved towards the cylindrical neck part for arresting the connecting element to the cylindrical neck part and sealing the circular closure plate against the circumferential rim.