A disposable cartridge (10), which is suitable to be used in a process of preparing a beverage, comprises a beverage making unit (1). A duct system (30) of the beverage making unit (1) has a main duct (31), a first subsidiary duct (32) which merges into the main duct (31), and a second subsidiary duct (33) which merges into the main duct (31) as well, at a different position than the first subsidiary duct (32). In a process of preparing a beverage, a first fluid is supplied by the main duct (31), and flows of a second fluid are supplied by the subsidiary ducts (32, 33). In this way, it is achieved that the second fluid is mixed with the first fluid in two steps. In case the second fluid is used for heating the first fluid, local boiling of the first fluid is prevented.