Abstract: The invention relates to a method for the in-line processing of liquid or pasty or semi-liquid media or further, media which contain solid elements in a liquid base, in pipe for conveying the medium between two steps in a plant by direct injection of a cryogenic fluid into the pipe, characterized in that the method uses, for the injection into the pipe, an injection device including a hollow cylindrical body in which a valve urged by a spring is inserted, said injection device including a through-channel substantially parallel to said valve and supplied with a pressurized cryogenic fluid, wherein one end of the through-channel is connected to the cryogenic fluid supply system while the opposite end opens at the seat of the valve.