Method for operating a washing machine with a container, a drum for receiving items of laundry, a drive motor for the drum, an impedance sensor in the container for determining an impedance signal as a function of a composition of an aqueous liquid in the container, and a control facility, wherein the following steps are carried out: (a) providing the container with an aqueous liquid containing tenside with a tenside concentration c Tenside so that the relationship c CMC ≤ c Tenside < c limit is fulfilled, wherein c CMC is a critical micelle formation concentration and c limit is a predetermined maximum permitted micelle concentration, and wherein the critical micelle formation concentration (c CMC) is the tenside concentration c Tenside, from which the tenside accumulates in the wash liquor in the form of micelle; (b) measuring the tenside concentration c Tenside in the aqueous liquid containing tenside and provided in step (a) by recording and evaluating impedance signals of the impedance sensor using an association, stored in the control facility, between the impedance signals and the tenside concentrations; (c) carrying out a wash phase so that with an established tenside concentration c Tenside < c CMC an additional dosage of detergent is carried out and/or a movement program of the drum stored in the control facility is carried out for this tenside concentration; characterised in that with an established tenside concentration c Tenside ≥ c limit, a dilution of the aqueous liquid containing tenside is carried out until the relationship c CMC ≤ c Tenside < c limit is fulfilled, and the movement program of the drum carried out in step with an established tenside concentration c Tenside < c CMC consists in a duration of the wash phase being greater and/or the entry of the kinetic energy being greater than in a wash phase in which the tenside concentration c Tenside fulfils the relationship c CMC ≤ c Tenside < c limit. (a) providing the container with an aqueous liquid containing tenside with a tenside concentration c Tenside so that the relationship c CMC ≤ c Tenside < c limit is fulfilled, wherein c CMC is a critical micelle formation concentration and c limit is a predetermined maximum permitted micelle concentration, and wherein the critical micelle formation concentration (c CMC) is the tenside concentration c Tenside, from which the tenside accumulates in the wash liquor in the form of micelle; (b) measuring the tenside concentration c Tenside in the aqueous liquid containing tenside and provided in step (a) by recording and evaluating impedance signals of the impedance sensor using an association, stored in the control facility, between the impedance signals and the tenside concentrations; (c) carrying out a wash phase so that with an established tenside concentration c Tenside < c CMC an additional dosage of detergent is carried out and/or a movement program of the drum stored in the control facility is carried out for this tenside concentration; characterised in that with an established tenside concentration c Tenside ≥ c limit, a dilution of the aqueous liquid containing tenside is carried out until the relationship c CMC ≤ c Tenside < c limit is fulfilled, and the movement program of the drum carried out in step with an established tenside concentration c Tenside < c CMC consists in a duration of the wash phase being greater and/or the entry of the kinetic energy being greater than in a wash phase in which the tenside concentration c Tenside fulfils the relationship c CMC ≤ c Tenside < c limit. with an established tenside concentration c Tenside < c CMC an additional dosage of detergent is carried out and/or a movement program of the drum stored in the control facility is carried out for this tenside concentration; characterised in that with an established tenside concentration c Tenside ≥ c limit, a dilution of the aqueous liquid containing tenside is carried out until the relationship c CMC ≤ c Tenside < c limit is fulfilled, and the movement program of the drum carried out in step with an established tenside concentration c Tenside < c CMC consists in a duration of the wash phase being greater and/or the entry of the kinetic energy being greater than in a wash phase in which the tenside concentration c Tenside fulfils the relationship c CMC ≤ c Tenside < c limit.