Stirrer

A stirrer having:

• a motor;
• a hollow shaft that is drivable via the motor and is provided with at least one additive outlet opening, via which an additive passed through the hollow shaft or a feed tube guided therein can be discharged;
• a first rotor arranged on the hollow shaft and having a first plurality of rotor blades disposed about the circumference of the hollow shaft, the first plurality of rotor blades having suction sides facing in a first axial direction with respect to the hollow shaft, and the first plurality of rotor blades having pressure sides facing in a second axial direction with respect to the hollow shaft;
• and
• a second rotor arranged on the hollow shaft at a distance from the first rotor and having a second plurality of rotor blades disposed about the circumference of the hollow shaft, the second plurality of rotor blades having suction sides facing in the second axial direction with respect to the hollow shaft, and the second plurality of rotor blades having pressure sides facing in the first axial direction with respect to the hollow shaft wherein
• the at least one additive outlet opening is provided between the two rotors;
• and
• the rotors are designed and drivable such that, during operation, a negative pressure and a centrifugal force are generated in an intermediate space defined between the rotors.