Abstract: The neck of a bottle is closed and sealed by a one-piece cap having a cylrical portion which surrounds the neck, a deformable end wall which extends across the open end of the neck, and a flexible hose which is integral with the end wall. The inner side of the end wall has an annular bead which sealingly engages the inner surface of the neck when the pressure in the interior of the bottle is reduced below atmospheric pressure. An annular groove at the inner side of the end wall surrounds the bead and communicates with the atmosphere by way of at least one channel in the cylindrical portion. The groove communicates with the atmosphere during expulsion of air from the bottle, for example, in response to heating, but is sealed from the interior of the bottle when the end wall bulges inwardly and maintains the bead in sealing engagement with the neck.