A system for cooking and then cooling food products by immersion in a heat transfer fluid, consisting of a vessel (200) to contain the heat transfer fluid and a system (500) for homogenization by blowing gas bubbles into the heat transfer fluid from a gas bubble formation system (530). The vessel (200) is closed by a cover (250) leaving a space above the maximum level of the free surface of the heat transfer fluid. Homogenization is accomplished by closed circulation of gas contained in the space above the heat transfer fluid which generates bubbles in the heat transfer fluid.