A laboratory-scale continuous countercurrent steep system for corn wet-milling - Part II. Evaluation of system stability

The purpose of this work was to evaluate the stability of a countercurrent steep system to ensure that variables, including temperature, pump flow rat e and steepwater profiles remain stable during long periods of operation. F our runs of a laboratory-scale continuous countercurrent steep system were used to evaluate its thermal and mechanical stability. One run was started with fresh steepwater while the other three were inoculated with light stee pwater obtained from a wet-milling plant. Variables, such as steep temperat ure, steepwater recycle rate and light steepwater draw rate, were monitored Steepwater characteristics, including pH, SO2 concentration, lactic acid c oncentration and steepwater solids content were determined. Six to eight da ys were required for all of the steepwater variables (pH, SO2 and lactic ac id concentration and steepwater solids content) to reach steady state when light steepwater from a plant was used to inoculate the system. When fresh steepwater was used, 12 d were needed. The average steep temperature of the 16 tanks during 16 d of continuous operation was 50 +/- 1 degrees C with a setpoint of 50 +/- 2 degrees C. The average pump flow rate for the 8 pumps was 5.0 +/- 0.1 mL/s when. the setpoint was 5.0 mL/s. The average light st eepwater draw rate over nine days was 593 +/- 49 mL/kg when the setpoint wa s 600 mL/kg. Corn steeped in this system was wet-milled and product yields were reproducible.