Oil quality sensor to determine the quality of deep-frying oil by measuring the capacitance of the deep-frying oil in a deep fryer: - with a housing and a hollow space in the housing, through which the deep-frying oil can be guided, - with an inlet opening to introduce deep-frying oil in the hollow space, - with a drain opening to drain the deep-frying oil out of the hollow space, - with a first electrode that extends along the hollow space, - with a second, electrode that extends along the hollow space, arranged opposite the first electrode, in which case the two electrodes (15, 20) form a capacitor being configured either as a cylinder capacitor, in which the second electrode encloses the first electrode and through which the deep-frying oil can be guided to measure its capacitance, or as a tube capacitor, in which the two electrodes (15, 20) are executed as half shells whose concave surfaces lie opposite each other by forming a space through which the deep-frying oil can be guided to measure its capacitance, - with a first temperature sensor to measure the temperature of the deep-frying oil that needs to be measured, and - with an evaluation unit configured to record the measured capacitance of the capacitor and the measured temperature, to digitalize these measured values and to calculate the polar fractions in the deep-frying oil by using these measured values, in which case these polar fractions are a criterion for the quality of the deep-frying oil characterized in that a second temperature sensor is provided and that the evaluation unit is configured to convert the measured temperature values of said second temperature sensor together with the measured temperature values of the first temperature sensor into a combined preferably average temperature. - with a housing and a hollow space in the housing, through which the deep-frying oil can be guided, - with an inlet opening to introduce deep-frying oil in the hollow space, - with a drain opening to drain the deep-frying oil out of the hollow space, - with a first electrode that extends along the hollow space, - with a second, electrode that extends along the hollow space, arranged opposite the first electrode, in which case the two electrodes (15, 20) form a capacitor being configured either as a cylinder capacitor, in which the second electrode encloses the first electrode and through which the deep-frying oil can be guided to measure its capacitance, or as a tube capacitor, in which the two electrodes (15, 20) are executed as half shells whose concave surfaces lie opposite each other by forming a space through which the deep-frying oil can be guided to measure its capacitance, - with a first temperature sensor to measure the temperature of the deep-frying oil that needs to be measured, and - with an evaluation unit configured to record the measured capacitance of the capacitor and the measured temperature, to digitalize these measured values and to calculate the polar fractions in the deep-frying oil by using these measured values, in which case these polar fractions are a criterion for the quality of the deep-frying oil characterized in that a second temperature sensor is provided and that the evaluation unit is configured to convert the measured temperature values of said second temperature sensor together with the measured temperature values of the first temperature sensor into a combined preferably average temperature.