Effects of Steep Time and SO2 Concentration on Steepwater Profiles and Maize Milling Yields Using a Continuous Countercurrent Steep System

Abstract

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, 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.