Abstract: A stopper includes a hollow casing with a resilient, ribbed sleeve that forms a valve seat. An interior plunger has a tip configured to mesh with the valve seat when in its down position and to open the valve when in its up position. An upper flange in the plunger provides an additional seal and is visible through a transparent wall in the casing. A vacuum in the bottle draws the plunger downward increasing the pressure with which the plunger presses against the seat, thus securing a long-lasting seal that maintains the vacuum in the bottle. When the vacuum is released, the resilience of the seat structure pushes the plunger upward, rendering it visible as an indicator of vacuum through the transparent wall. An opening in the casing allows connection to a pump to create the vacuum in the bottle.