A pouring stopper intended to be attached to a neck of a container for liquids, comprising at least: - a hollow body having a general shape with a surface of revolution about a central axis, the hollow body defining an actuation chamber open at a first end of the hollow body and a feed chamber open at a second end of the hollow body, the feed chamber being configured to open into the container when the pouring stopper is attached to the neck of the container, the hollow body also defining an air inlet channel between a first opening in the surface of revolution and a first opening opening into the feed chamber and a liquid outlet channel between a second opening in the surface of revolution and a second opening opening into the feed chamber, the air inlet channel being separate from the liquid outlet channel, the first opening in the surface of revolution and the second opening on the surface of revolution being adjacent, the hollow body comprising a fixing element configured to fix the pouring stopper to the container; - a push button able to slide in the actuation chamber parallel to the central axis; - a valve integral with the push button, the valve comprising a valve head and a stem, the valve being configured so as to be alternately in a closed position in which the valve head closes off the first opening opening into the feed chamber and the second opening opening into the feed chamber, and an open position in which the valve head does not close off the first opening opening into the feed chamber and the second opening opening into the feed chamber, the stem extending parallel to the central axis between the push button and the valve head, passing through the air inlet channel and the liquid outlet channel; - an elastic element tending to bring the valve into the closed position when a pressure lower than a predetermined pressure is applied to the push button and to leave the valve in the open position when a pressure greater than or equal to the predetermined pressure is applied to the push button, characterised in that the valve head comprises a flat portion lying in a plane substantially perpendicular to the stem, the flat portion being surrounded by a seal, the hollow body comprising a counter seal surrounding the first opening opening into the feed chamber and the second opening opening into the feed chamber, the seal of the valve head being configured to contact the counter seal when the valve is in the closed position, the seal being configured to deform when it contacts the counter seal. - a hollow body having a general shape with a surface of revolution about a central axis, the hollow body defining an actuation chamber open at a first end of the hollow body and a feed chamber open at a second end of the hollow body, the feed chamber being configured to open into the container when the pouring stopper is attached to the neck of the container, the hollow body also defining an air inlet channel between a first opening in the surface of revolution and a first opening opening into the feed chamber and a liquid outlet channel between a second opening in the surface of revolution and a second opening opening into the feed chamber, the air inlet channel being separate from the liquid outlet channel, the first opening in the surface of revolution and the second opening on the surface of revolution being adjacent, the hollow body comprising a fixing element configured to fix the pouring stopper to the container; - a push button able to slide in the actuation chamber parallel to the central axis; - a valve integral with the push button, the valve comprising a valve head and a stem, the valve being configured so as to be alternately in a closed position in which the valve head closes off the first opening opening into the feed chamber and the second opening opening into the feed chamber, and an open position in which the valve head does not close off the first opening opening into the feed chamber and the second opening opening into the feed chamber, the stem extending parallel to the central axis between the push button and the valve head, passing through the air inlet channel and the liquid outlet channel; - an elastic element tending to bring the valve into the closed position when a pressure lower than a predetermined pressure is applied to the push button and to leave the valve in the open position when a pressure greater than or equal to the predetermined pressure is applied to the push button,