An admixing system for fire extinguishing systems for producing an extinguishing agent / extinguishing agent additive mixture -premix- by admixing an extinguishing agent additive, in particular a foaming agent, to an extinguishing agent, in particular water, comprising - a motor, in particular a water motor, able to be driven by a flow of extinguishing agent which has an inlet for supplying the extinguishing agent to the motor, in particular from an extinguishing agent tank or from an extinguishing agent supply line, an outlet for discharging the extinguishing agent from the motor, and an output shaft able to be driven by the motor, - an admixing pump, in particular a piston pump, for conveying the extinguishing agent additive which has an input shaft coupled to the output shaft of the motor, an input for providing the extinguishing agent additive, in particular from an extinguishing agent additive tank or from an extinguishing agent additive supply line, and an output for discharging the extinguishing agent additive, - an admixing line having a first motor-side end and a second outlet-side end, wherein the motor-side end is fluidly connected to the outlet of the motor, - an extinguishing agent additive line having a first pump-side end and a second admixing line-side end, wherein the pump-side end is fluidly connected to the output of the admixing pump and the admixing line-side end is fluidly connected to the admixing line at an admixture point, which is different from the motor-side end of the admixing line, - a branching line with a first, admixing line-side end and a second, outlet-side end, wherein the admixing line-side end is fluidly connected to the admixing line at a branching point located between the motor-side end of the admixing line and the admixture point, and - a branching valve arranged in the branching line, characterized in that the admixing system additionally comprises a motor rotational speed measuring device and a controller, and that the controller is designed to fully or partially open and/or close the branching valve on the basis of the rotational speed of the motor measured by the motor rotational speed measuring device. - a motor, in particular a water motor, able to be driven by a flow of extinguishing agent which has an inlet for supplying the extinguishing agent to the motor, in particular from an extinguishing agent tank or from an extinguishing agent supply line, an outlet for discharging the extinguishing agent from the motor, and an output shaft able to be driven by the motor, - an admixing pump, in particular a piston pump, for conveying the extinguishing agent additive which has an input shaft coupled to the output shaft of the motor, an input for providing the extinguishing agent additive, in particular from an extinguishing agent additive tank or from an extinguishing agent additive supply line, and an output for discharging the extinguishing agent additive, - an admixing line having a first motor-side end and a second outlet-side end, wherein the motor-side end is fluidly connected to the outlet of the motor, - an extinguishing agent additive line having a first pump-side end and a second admixing line-side end, wherein the pump-side end is fluidly connected to the output of the admixing pump and the admixing line-side end is fluidly connected to the admixing line at an admixture point, which is different from the motor-side end of the admixing line, - a branching line with a first, admixing line-side end and a second, outlet-side end, wherein the admixing line-side end is fluidly connected to the admixing line at a branching point located between the motor-side end of the admixing line and the admixture point, and - a branching valve arranged in the branching line,