Corn steep liquor is a byproduct of the initial stages of wet milling of corn.
Steeping of corn(i.e., soaking in water) aids in the separation the various components of corn such as starch and nutrients. Corn is normally steeped in stainless steel drums holding from 3,000-25,000 bushels of corn . Approximately 5-9 gallons of water per bushel of corn is added to the tank . The water originates elsewhere in the wet milling process where it has already obtained some soluble corn matter. The temperature of the water is maintained at 45-54˚C by heating the water as it is recirculated or by using a heat exchanger . Immediately before adding the water to drums, an aqueous source of sodium dioxide is added to the water to a concentration of 0.1-0.2% . In water, these sources of sodium dioxide form sulfurous acid, which controls fermentation and softens the corn kernel to aid in the separation of the corn products.
Most of the sulfurous acid is absorbed by the corn kernels so that after ten hours the concentration of sulfurous acid in the steepwater is lowered to 0.01% .
The corn is steeped for anywhere between 22-50 hours, while the CSL is moved through six to twelve successive steeping tanks. The CSL is initially added to the tank with the oldest corn so that it is in contact with the highest concentration of the sulfurous acid. The water is then moved to fresher corn so that the oldest CSL is in contact with the freshest corn. Approximately one- third of the water is absorbed by the corn during the steeping, and the other two-thirds is withdrawn from the steeping system as light steepwater that contains between 6-9% solids by weight. The light steepwater is then evaporated until it contains 40-60% solids. The resulting CSL may be further processed by downstream users to meet their own specifications.