ABSTRACT Response surface methodology with a 3 × 3 factorial plan design was used to investigate the effects of starch content (60–70 g/100 g dry matter [DM]), lipid content (6.2–10.2 g/100 g DM) and moisture content (10–16 g/100 g wet matter [WM]) on extrusion behavior of rice-based blends, on the physicochemical properties of extrudates, and the apparent viscosity of resulting gruels. The increase in starch content increased the loss of lipid, the expansion ratio, the degree of gelatinization (DG) of starch, and the water absorption index (WAI). Increasing lipid content resulted in higher loss of lipids and a lower WAI and water solubility index (WSI). Water content had the most influence. Increasing water content resulted in increased loss of lipids, higher moisture content of extrudates, and in lower die temperature, expansion ratio, DG, WAI and WSI. The high DG (≥91%) of all extrudates demonstrated that the very-low-cost extruder manufactured in Vietnam is suitable for the production of ready-to-eat infant flour. PRACTICAL APPLICATIONS This work tested and optimized the effect of blend composition on the characteristics of rice-based extrudates obtained using a very-low-cost extruder (VLCE) manufactured in Vietnam and on derived gruels. Our results enable prediction of the characteristics of extruded products, when the starch, lipid and water contents of the blends are known. Thus, VLCE users will be able to choose the nature and relative proportion of ingredients to obtain extrudates with specific targeted characteristics. In addition, this study demonstrated that serious loss of lipids occurs during extrusion of blends with high lipid contents. To obtain the lipid content recommended for complementary food, it is thus preferable to add ingredients with high lipid content after extrusion. We conclude that this kind of VLCE manufactured in Vietnam is suitable for low-cost production of instant flour with all the required characteristics for use as complementary foods for infants and young children after the age of 6 months.