Abstract Microstructural changes which occur during the extrusion cooking of maize grits were studied using optical microscopy and X-ray diffraction. The complete disruption of the maize grit particles and their constituent starch granules was found to be related to changes in extruder die pressure, screw torque and product solubility and water absorption. The disruption was found to depend upon extrusion moisture, barrel temperature and screw configuration. It occurred over a narrow range of specific mechanical energy input, 115–145 W h kg −1. The E-type form of the crystalline amylose-lipid complex was found to occur throughout the temperature range 90–150°C when the maize grit was extruded with low conveying efficiency screws.