Abstract: A device is provided which simulates heat transfer into a flexible pouch in which food or like product is cooked and sterilized. The simulator is a block of polymeric material having a thickness approximately that of a food pouch and a thermal diffusivity generally equal to or slightly above that of food product. A thermal sensor is disposed centrally within the block of polymer material and is connected to electrical leads extending externally of the retort to apparatus that records temperature change as a function of time. A plurality of simulators are placed at various regions in the retort, and the uniformity of the heat transfer under certain operating conditions is determined by measuring the heating rates of the several simulators. Operating conditions, such as flow rates or location of introduction of water, steam and air are changed until a sufficiently uniform heat transfer environment is achieved.