The invention relates to a product sterilization or pasteurization method. The inventive method includes: transferring a product from outside to inside a pressurized inlet compartment of a chamber through at least one pressurizing airlock; loading the product onto a conveyor to transfer the product through the chamber from the inlet compartment to an outlet compartment; heating the product by dipping the product in hydrostatic columns while applying variable pressure and temperature; passing the product through an intermediate pressurizing compartment; cooling the product by dipping the product in hydrostatic columns while applying variable pressure and temperature; unloading the product from the conveyor at a pressurized outlet compartment; and transferring the product to the exterior from the outlet compartment through at least one atmospheric pressurization airlock.