Stopper for closing neck of container

A method for manufacturing a stopper for closing a neck of a container, the method comprising:

• injecting plastic into a molding cavity so as to form the stopper in one piece, the stopper including:
• a sealing membrane configured to seal off the neck of the container, and being provided with a central opening,
• a skirt configured to be attached to the neck of the container,
• a tubular stem centered on an axis and extending from the sealing membrane around the central opening, and
• a capsule connected, by a tear wall, to a free end of the stem, the free end facing away from the sealing membrane, wherein the capsule is configured to be wedged in the stem to seal the neck of the container after being separated from the remainder of the stopper by breaking the tear wall,
• while the tear wall is intact, applying a force along the axis to the stopper so as to, in a single movement of the capsule relative to the remainder of the stopper, break the tear wall and move the capsule inside the stem until the capsule is wedged in the stem.