The invention relates to a seal (10) for an appliance (1) for cooking food under pressure, including a vessel (2) and a lid (3) defining a cooking chamber (5), said seal comprising a heel (11) from which at least one first lip (12) projects, said lip having at least one release window (20) bored therein, extending through the body (e) of the lip, said first lip (12) also forming a differential moving member enabling the release window (20) - when the pressure inside the cooking chamber (5) exceeds a predetermined threshold - to perform a movement in relation to the heel (11) that enables said release window (20) to open a release opening by means of which said cooking chamber (5) is placed in communication with the outside of the appliance (1). The invention also relates to appliances for cooking food under pressure.