Influence of process and product variables on extrusion energy and pressure requirements

Energy and pressure requirements for processing foods as affected by product moisture content and extruder barrel temperature and screw speed were studied using corn gluten meal (CGM) processed in a C.W. Brabender laboratory single-screw cooker-extruder. The extruder screw was 1·9 cm in diameter, had a 3:1 compression ratio and a 20:1 barrel length-to-diameter ratio. The die-end nozzle was 3 mm in diameter. Moisture contents were 14, 20 and 26% (dry basis), extruder barrel temperatures were 120, 145 and 170°C and the extruder screw speeds were 100, 150 and 200 rpm. Regression analysis showed that moisture content contributed most to the variation in energy requirements (32·4%), followed by temperature (12·4%). Effect of screw speed was found to be insignificant. Increasing moisture content and barrel temperature caused specific energy to decrease. Pressure was found to be significantly affected and decreased with increases in all three variables.