The inventions relates to an extrusion apparatus suited for water-containing products which heat-expand by internal boiling of water by pressure relief after passing through extrusion nozzles. The apparatus comprises a) an extruder, which at the outlet end thereof comprises a nozzle plate, b) a pressure-controlling chamber for controlling the pressure on the outlet side of the nozzle plate, said pressure-controlling chamber possibly containing a cutting-off unit, and c) a sluice unit downstream of the pressure controlling chamber. The apparatus furthermore comprises that the pressure-controlling chamber and sluice unit being releasably interconnected and at least the sluice unit being mounted movably in and out of the product stream. Hereby may the apparatus start up without connecting the sluice and easily connecting the sluice, when the product is sufficiently stable for the correct function of the sluice, so that the problems during start-up of the apparatus, such as the unstable and the relatively wet products tendency of blocking the sluice is substantially avoided.