An apparatus for sterilising a packaged product (16) such as food or drink comprises a pair of gas filled electrodes (1, 2) connected to a power supply (18) for generating a high voltage pulses between the electrodes (1, 2) sufficient to ionise the gas therein and to create a high electromagnetic field therebetween. A reflector (7) is provided for directing the generated field towards the package (16), such that the electromagnetic field penetrates through the wall of the package (16) and forms cold plasma from the trapped air inside the package (16). This cold plasma comprises ozone and other reactive oxygen based species which have a high oxidizing potential and kill all microorganisms in contact with the ozone and reactive species resulting in the disinfection of the product as well as the interior of the sealed package.