A system for measuring the state of degradation of cooking oil or fat includes at least one fryer pot. A conduit is fluidly connected to the fryer pot for transporting cooking oil from the fryer pot and returning the cooking oil back to the fryer pot. A pump is provided for re-circulating cooking oil to and from the fryer pot. A sensor is disposed in fluid communication with the conduit and measures an electrical property of the cooking oil as the cooking oil flows past the sensor and is returned to the at least one fryer pot.