Coffee machine, in particular fully automatic coffee machine, and method for operating a coffee machine

A coffee machine (10), comprising a water tank (11), a heating device (16) for heating water, a brewing unit (18) for leaching out ground coffee beans via water heated in the heating device (16), a water line system (13) encompassing at least one water line, as well as a feed pump (14) for conveying water out of the water tank (11) through the water line system (13), wherein a chamber (25) is or can be provided for a chemical active ingredient, and can be manually or automatically hooked up and/or connected to the water line system (13) in such a way that water can be conveyed out of the water tank (11) via the feed pump (14) through the chamber (25) and into the water line system (13), wherein

• the chamber (25) has allocated to it an adding valve (27) that can be adjusted between a first switching position in which the stream of water conveyed by the feed pump can be completely conveyed in the water line system while circumventing the chamber (25), and a second switching position in which the chamber (25) is hooked up, and the stream of water conveyed by the feed pump can be partially or completely conveyed through the chamber (25),
• and/or
• the chamber (25) in or on the coffee machine (10) can be adjusted between a first position in which the chamber (25) is decoupled from the water line system (13) and a second position in which the chamber (25) is connected to the water line system (13).