A method for heat treating a packaged product includes providing a channel with a liquid disposed therein, the channel having a electrodes disposed in and spaced apart along a treatment portion of the channel, pressurizing the liquid in the treatment portion of the channel, transporting the packaged product, including a product disposed within a package, along the channel including transporting the packaged product through the treatment portion of the channel, heating the packaged product in the treatment portion of the channel including causing emission of radio frequency waves between the plurality of electrodes and into the treatment portion of the channel including forming an electrical field in the treatment portion of the channel, and shielding the electrical field in the treatment portion of the channel using a shield which forms a cavity around the treatment portion of the channel, the cavity being configured to substantially confine the electrical field.