Device for closing beverage containers and assembly of such a device and a beverage container

A method for operating an assembly comprising a basic structure configured to couple to a beverage container and enclosing at least one passage channel for a beverage, a closing element releasably coupled to the basic structure for closing the at least one passage channel, at least one axially displaceable holder arranged at least partially in the passage channel and at least partially filled with an additive to be added to the beverage, wherein an upper side of the holder to be opened facing toward the closing element and an underside of the holder remote from the closing element initially close the holder, and at least one lower perforation structure positioned under an underside of the holder remote from the closing element and configured to perforate the underside of the holder during downward displacement of the holder in the passage channel in the direction of the lower perforation structure, whereby the additive can be released into the beverage in the beverage container, the method comprising the steps of:

• A) uncoupling the closing element relative to the basic structure,
• B) opening the upper side of the holder, and
• C) displacing the holder downward in the direction of the lower perforation structure such that the underside of the holder is perforated and the additive can be released into the beverage in the beverage container.