Plug for high-pressure processing machines with a bag, comprising a duct for the passage of a pressure-transmitting fluid to the bag, another duct for filling and emptying of a product to be pressurized and a valve. The plug is further provided with a rod for opening and closing the valve. Said rod is located in the duct for the product and has its own inner duct joined to a cleaning agent chamber for the passage of the cleaning agent through the product duct. The invention also relates to a machine incorporating said plug and a method for the processing of pumpable substances. Hygienic design and very high pressure sealing requirements are met by the invention.
