A container (10) assembly for accommodating a carbonated beverage defining a temperature dependent internal carbonization pressure comprises a beverage container (10, 12) having a body part defining an inner volume for accommodating the carbonated beverage and a cylindrical neck part defining a gas filled head space. The cylindrical neck part further defines a circumferential rim (16, 18) defining an opening (18, 20) and an outwardly oriented surface (24, 26) which extends between the rim (16, 18) and the body part, and has an outwardly oriented circumferential flange (20, 22). The beverage container (10, 12) further defines a burst pressure being higher than the temperature dependent internal carbonization pressure at room temperature. A closure (30, 32) is provided and comprises a closure plate (32, 34) and a cylindrical part. The closure plate (32, 34) covers the opening (18, 20) at the rim (16, 18) and the cylindrical part covers the neck part. The cylindrical part comprises a locking part for arresting the outwardly oriented circumferential flange (20, 22). A flexible sealing ring (10, 40) is provided and is movable between a first position in which the sealing ring (10, 40) is accommodated in a compressed state entirely within a circumferential cavity defined between the cylindrical part of the closure (30, 32) and the outwardly oriented surface (24, 26) of the neck part when the temperature dependent internal carbonization pressure is lower than or equal to the temperature dependent internal carbonization pressure at room temperature, and, a second position in which a larger part of the sealing ring (10, 40) is accommodated in a compressed state within the circumferential cavity, and a smaller part of the sealing ring (10, 40) is located in an uncompressed state within a groove (28, 30) in the cylindrical part and/or in the outwardly oriented surface (24, 26).