Abstract: A hand-operated vacuum pump is combined with a resilient closure sleeve for sealing and de-pressurizing the open space within a fermented beverage container. A pump cylinder is covered by a resilient closure sleeve which is insertable into the neck of the beverage container. A piston is coupled for extension and retraction through the pump cylinder. The piston carries a floating seal which is axially movable along a reduced diameter portion of the piston for opening and closing an air inlet port between an air transfer annulus and an evacuation chamber. The pump includes an improved check valve assembly in which a suction port is sealed by a resilient membrane which engages a tapered sealing surface in which the suction port is formed.