Effects of steep time and SO₂ concentration on steepwater profiles and maize milling yields using a continuous countercurrent steep system

Effects of SO₂ concentration and steep time on maize steep profiles and wet milling results were studied using a continuous countercurrent steep system. Maize was steeped at 50 ± 2 °C at different SO₂ concentrations (target value at 1,000, 2,000 and 3,000 ppm) for different lengths of time (18, 24, 30 and 36 h). Steepwater profiles, including pH, 7 SO₂ concentration, total acidity and steepwater solids content versus tank number for each combination of SO₂ level and steep time were generated. Three steeped maize samples for each condition were milled and average product yields were reported. Steeping, from the perspective of maize, can be viewed as a three-stage process including a lactic acid dominated stage, a SO₂ absorption stage and a SO₂ diffusion stage. From the perspective of steepwater, increasing SO₂ concentration increases the total dry solids increase rate and SO₂ decrease rate. Starch yield can be significantly increased by increasing either steep time or SO₂ concentration.