Reactor for converting water-containing biogenic mass and/or carbon-containing synthetic material into a carbon-containing dry matter with a dry matter content (TS_g) of at least 85%, in particular at least 90%, and for generating water vapour, wherein the reactor comprises: a control unit for controlling the operation of the reactor, a reactor container with a container wall, a filling chamber surrounded by the container wall for receiving the mass to be converted, a stirrer arranged within the filling chamber, a heating device (12, 18) for heating the mass to be converted received in the filling chamber, such that the mass to be converted releases water in form of water vapour due to the heating up in the filling chamber (drying), wherein the heating device (12, 18) comprises a heating chamber which is arranged within the filling chamber, such that the heating chamber at its outer circumference gives off heat into the filling chamber, a vapour outlet for discharging the water vapour, and at least one substance container (50, 51) for receiving the dry matter, wherein the at least one substance container is connected via an outlet at the container wall to the filling chamber, wherein the stirrer is adapted to prevent during drying aggregation and solidification, respectively, of the dry matter in the filling chamber, characterized in that the heating chamber comprises a line inlet for feeding water and/or water vapour, such that for the heating function water vapour is generatable in the heating chamber itself and/or is transportable from outside into the heating chamber, and for supplying the filling chamber with water vapour a line inlet of the filling chamber is interruptedly connected with a line outlet of the heating chamber. a control unit for controlling the operation of the reactor, a reactor container with a container wall, a filling chamber surrounded by the container wall for receiving the mass to be converted, a stirrer arranged within the filling chamber, a heating device (12, 18) for heating the mass to be converted received in the filling chamber, such that the mass to be converted releases water in form of water vapour due to the heating up in the filling chamber (drying), wherein the heating device (12, 18) comprises a heating chamber which is arranged within the filling chamber, such that the heating chamber at its outer circumference gives off heat into the filling chamber, a vapour outlet for discharging the water vapour, and at least one substance container (50, 51) for receiving the dry matter, wherein the at least one substance container is connected via an outlet at the container wall to the filling chamber, wherein the stirrer is adapted to prevent during drying aggregation and solidification, respectively, of the dry matter in the filling chamber, characterized in that the heating chamber comprises a line inlet for feeding water and/or water vapour, such that for the heating function water vapour is generatable in the heating chamber itself and/or is transportable from outside into the heating chamber, and for supplying the filling chamber with water vapour a line inlet of the filling chamber is interruptedly connected with a line outlet of the heating chamber.