In an apparatus for foaming a liquid with an aerating device by which the liquid can be aerated, an outlet arrangement which is in communication with the aerating device via a conduit and a pump arranged in the conduit for transporting the aerated liquid from the aerating device to the outlet arrangement, at least one flow resistor is provided in the conduit or the outlet arrangement which includes a plurality of adjacent resistor elements of an elastic material which are movable relative to one another and between which there are passages through which the aerated liquid is forced whereby a high quality stable foam is generated and a pump control arrangement is provided for maintaining the aerated liquid under pressure.