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, characterised in that the method uses, for the injection into the pipe, an injection device (3) including a hollow cylindrical body in which a valve (17) urged by a spring (19) is inserted, said injection device including a through-channel (18) substantially parallel to said valve and supplied with a pressurised 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 (13) of the valve.
