Abstract: There is described a circuit arrangement for checking liquid food for contaminants which can be reliably operated fully automatically or at least by completely untrained staff. It comprises a conductivity measuring probe, whose output signal is processed by a transducer. From the output signal from the transducer there is substracted an amount in such a way that there is obtained a voltage which is independent of the individual nominal data of the batch. This independent constant voltage is made the reference point of a "window" of allowable deviations, the width of this window being independent of the individual batch data. The balancing of the circuit arrangement to the individual conductivity nominal value of the respective liquid food batch checked is the only change of voltages within the circuit arrangement, which takes place upon the transition from one liquid food batch to the next batch.