System and method for sensing oil quality

A system (10) for measuring the state of degradation of cooking oil in a deep fryer is provided. The system includes a loop of piping (20) fluidly connected to a fryer (100) for selectively allowing flow of oil from the fryer and into the loop and for returning to the fryer. A pump urges the flow of cooking oil through the loop of piping and selectively to urge oil to return to the at least one fryer pot. The loop further comprises a return portion that extends from a discharge of the pump (220) toward a suction of the pump. A sensor (60) is disposed in the return portion of the loop and adapted to measure an electrical property that is indicative of total polar materials of said cooking oil. A vent line (500) is provided in the return portion of the loop.