Summary Low‐density expanded starchy products are often desirable, particularly in the snack food industry. Levels of shear and amylose are often deemed crucial factors for expansion. In this study, maize starches containing low (waxy), normal and high levels of amylose were compared after processing. Low shear processing used a popping head (similar to a rice‐cake machine), while high shear (~450 kJ kg−1) samples (pellets and directly expanded) were created using twin‐screw thermomechanical extrusion. Native starches and ground extruded materials (<106 µm) were popped using the same conditions (230 °C, 4 s, water content 12% wwb). All samples tested created fused aerated cakes, which had little or no remaining crystallinity, except for the directly popped waxy sample, which retained ~17% of its original crystallinity. Water absorbances and solubilities were influenced greatly by the starch source and marginally by the amount of processing. On processing, waxy samples showed increased solubility while those with normal amylose content had greater absorption. The densities of all the popped samples were similar despite marked differences in shear regime history and the major variations in the amylose and amylopectin ratios. These results challenge the expected relationships between shear and different starches’ potential to expand.

Aerated starch products are a staple of the food industry, with particular relevance in the snack market. Water plays a crucial role in the formation of such products due to its utility both as a blowing agent and as a starch plasticiser. Amylose/amylopectin ratio and shear are traditionally also important factors in starch expansion. In this study, waxy, normal and high amylose maize starch variants were expanded using a rice-cake style popping head at water contents between 0% and 24%. This range of water contents was achieved by drying the material at 105 °C and then rehydrating by suspension over water at 50 °C until the desired water content was reached prior to popping. Sample types were further subdivided into low shear (native) and high shear (extruded) processing prior to popping. Processing history, amylose content and water content all influenced the water interaction properties of the popped products. However, density was largely governed by water content with little apparent influence of other factors. An optimum water content range to produce low-density (and therefore high desirability in industry) products was identified in the region of ~15-21% water. Samples popped below this range exhibited suboptimal expansion whilst those popped at higher water contents experienced violent blowout.