Abstract: An overpressure retort system includes a process vessel in fluid flow communication with a storage vessel. Heated process fluid from the storage vessel is transferred to the process vessel, including through spraying outlets or nozzles to direct heated process fluid onto the nutrient product containers. After the cooking process has been completed, the heated process fluid is returned to the storage vessel and then cool process fluid is used to cool the nutrient products in the process vessel, including by spraying the cooled process fluid onto the nutrient product containers. During the cooking and cooling processes, the process fluid from the process vessel is recirculated, and the overpressure within the process vessel is controlled by supplying compressed gas at a controlled pressure to the headspace of the process vessel. The headspace of the process vessel and the headspace of the storage vessel are in fluid flow communication.