A method of monitoring the temperature of a fryer used for snack food such as potato chips, the method comprising the steps of: providing a temperature probe 2 comprising a temperature sensor within a hermetically sealed casing； providing a fryer 50, the fryer containing a body of heated oil 52, the fryer having a product input end 54 and a product output end 54 with a product flow path 60 therebetween； floating the temperature probe on the oil along at least a part of the product flow path of the fryer, the temperature probe having a density less than the specific gravity of the oil； and recording a temperature profile corresponding to the temperature sensed by the temperature sensor of the temperature probe along the respective part of the product flow path. The fryer 50 includes conventional conveying apparatus 62, such as a helical screw, paddles or flights. There is also disclosed a temperature probe comprising a temperature sensor within a hermetically sealed casing, the temperature sensor being adapted to measure a temperature of at least 200°C and the hermetically sealed casing being thermally resistant to a temperature of at least 200"C, and a wireless transmitter within the easing and connected to the temperature sensor, the wireless transmitter being adapted to transmit a plurality of temperature values sensed by the temperature sensor over a period of time, the temperature probe having a density of no more than 925g/dm3 and the casing, optionally having a substantially spherical exterior surface.
