One goal of optimising cleaning processes is the economic use of surfactant. To find the optimum concentration of active surfactants for a stable and high cleaning quality, a measurement technique to determine this concentration is required, in order to establish a correlation to the cleaning result. The article introduces a modified surface tension measurement method to determine the concentration of active surfactants in process conditions. Based on this method, a new generation of inline tensiometers had been developed. These Instruments allow continuously monitoring the active surfactant concentration in a cleaning bath. The article shows how to interpret the measurement results for the process control. Exemplarily at the use of online measurement in metal cleaning processes, the potential to provide a higher level of process quality control will be illustrated.