A method for detecting properties of fluid media within a predetermined process using impedance spectroscopy, comprising the steps of: a) acquiring an initial impedance characteristic in a complex impedance plane over a predetermined frequency range at the beginning of the process, b) determining a plurality of characteristic points (P1 to P4) at discrete frequencies on the initial impedance characteristic as a measure of the properties of the fluid medium, and determining an initial value (Xwo) of the properties of the fluid medium based on the initial impedance characteristic and/or based on the characteristic points (P1 to P4), c) determining respective ambient frequency ranges around each of the characteristic points on the initial impedance characteristic as a respective part of the initial impedance characteristic with knowledge of the type of the fluid medium to be detected, d) performing further detections of actual impedance characteristics within and limited to the respective ambient frequency ranges around the characteristic points of the initial impedance characteristic, e) determining respective corresponding characteristic points (P1 to P4) of the actual detected parts of the impedance characteristic within the ambient frequency ranges of the initial impedance characteristic, f) determining differences between the characteristic points of each of the actual detected portions of the impedance characteristic for at least one of the characteristic points within the concerned ambient frequency range and the respective corresponding characteristic point of the initial impedance characteristic, and comparing the difference with a predetermined reference range determined in dependence on the initial value (Xwo) of the characteristics of the fluid medium, and g) performing control actions on the process to continue the process when the difference is within the reference range. a) acquiring an initial impedance characteristic in a complex impedance plane over a predetermined frequency range at the beginning of the process, b) determining a plurality of characteristic points (P1 to P4) at discrete frequencies on the initial impedance characteristic as a measure of the properties of the fluid medium, and determining an initial value (Xwo) of the properties of the fluid medium based on the initial impedance characteristic and/or based on the characteristic points (P1 to P4), c) determining respective ambient frequency ranges around each of the characteristic points on the initial impedance characteristic as a respective part of the initial impedance characteristic with knowledge of the type of the fluid medium to be detected, d) performing further detections of actual impedance characteristics within and limited to the respective ambient frequency ranges around the characteristic points of the initial impedance characteristic, e) determining respective corresponding characteristic points (P1 to P4) of the actual detected parts of the impedance characteristic within the ambient frequency ranges of the initial impedance characteristic, f) determining differences between the characteristic points of each of the actual detected portions of the impedance characteristic for at least one of the characteristic points within the concerned ambient frequency range and the respective corresponding characteristic point of the initial impedance characteristic, and comparing the difference with a predetermined reference range determined in dependence on the initial value (Xwo) of the characteristics of the fluid medium, and g) performing control actions on the process to continue the process when the difference is within the reference range.