Plug (5a) for high-pressure processing machines, comprising a bag (6), a duct (20) for the passage of a pressurising fluid to the bag, another duct (13) for filling and emptying a product to be pressurised and a valve (7). The plug is further provided with a rod (11) for opening and closing the valve. Said rod is located in the duct for the product and has its own inner duct (11a) connected to a cleaning agent chamber (12) for the passage of the cleaning agent through the product duct. The invention also relates to a machine comprising said plug and a method for processing pumpable substances. The invention makes it possible to meet requirements relating to hygienic design and tightness under a very high pressure.
