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 (CRA 2002; White and Johnson 2003). Approximately 5-9 gallons of water per bushel
of corn is added to the tank (Liggett and Koffler 1948; White and Johnson 2003). 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 (Liggett and Koffler 1948; CRA 2006a; White and
Johnson 2003). 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% (Liggett and Koffler 1948; White
and Johnson 2003). 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% (Liggett and Koffler 1948).
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withdrawn from the steeping system as light steepwater that contains between 6-9% solids by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 (White and
Johnson 2003; Budavari 1996).