Two chamber parts are pressed against each other in a sealing manner in order to receive a capsule. In an open position, the capsule can be held in an intermediate position between the chamber parts by a positioning unit having mutually opposite guide sections for guiding the capsule on mutually diametrically opposite sections of the capsule collar in order to hold the capsule in the intermediate position. The insertion section is formed as a hinged guide and the opposite guide section as a release guide. The release guide has a recess formed in such a way that the capsule can be rotated out of the intermediate position around the hinge guide and can be released from the release guide. Before reaching the closed position, the capsule is freed from the release guide in first and second movement phases by being acted on by one of the chamber parts.
