The effect of carbon dioxide injection into an extrusion cooker on extruder operation and extrudate structure was studied in the absence of steam expansion. The bulk density of extruded potato granules, maize and wheat starch decreased with the pressure of injected gas, although at higher pressures the extruded structure collapsed. The actual densities and structures achieved by carbon dioxide injection varied with extrusion conditions of feed rate, screw speed and barrel temperature. Carbon dioxide injection did not produce such expanded extrudates as conventional steam flashing. However, these structures were produced under low temperature and high moisture conditions, such that the starch component received minimal degradation as shown by the low solubility characteristics.