A method for producing a capsule includes providing a plastic main body having a bottom region, a peripheral side wall, and a peripheral main-body collar adjoining the peripheral side wall, wherein the main body has a substantially rectangular cross-section in the region of the main-body collar; providing a deep-drawn plastic cover for closing the capsule, wherein the cover forms an outward curvature, which adjoins a peripheral cover collar; filling the main body with an extraction material; and placing the cover onto the main body such that the cover collar lies on the main-body collar and fastening the cover collar to the main-body collar via ultrasonic welding. The cover is provided with an energy-director, which focuses the ultrasound energy during the ultrasonic welding, and wherein the cover has at least one groove that extends peripherally on an outer face in the region of the cover collar.