A continuous cooker having a continuous closed-loop cooking chamber which maintains a constant volume of liquid phase material and a constant volume of gas phase material therein. The cooker is provided with a liquid inlet on one side of the loop, and a common gas and liquid outlet on the other side of the loop. The loop is disposed to provide a lower passageway in which a constant volume of liquid resides, and an upper passageway in which a constant volume of pressurized gas resides. The cooker automatically maintains virtually constant retained-liquid volume regardless of discharge conditions. A gas, i.e., a material which is not condensed at operating conditions is continuously added to the upper passageway.