Corn Steep Liquor

By Lindsay Fernandez-Salvador, OMRI Review Program Manager

Corn steep liquor (a.k.a. condensed fermented corn extractives) is a by-product of the corn wet milling process. According to the Corn Refiners Association, “CSL is a viscous liquid mixture consisting entirely of water-soluble components of corn steeped in water” (Corn Refiners Association, 2006 [1]). Since the corn kernel is a complex mixture of starch, protein, oil, water, fiber, minerals and vitamins, the corn wet milling process yields many widely used products such as corn oil, corn germ meal, cornstarch and high fructose corn syrup. Corn is soaked, or “steeped” in 120°F to 130°F water containing 0.1%–0.2% sulfur dioxide for 24–48 hours. The sulfurous acid formed induces chemical and physical changes in the kernel, in effect separating the starch and insoluble protein by cleaving protein disulfide cross-links in the endosperm protein matrix. (Dailey, 2000.) The sulfurous acid also helps to control undesirable microorganisms, and allows dissolved sugars to be converted to lactic acid, which helps to maintain a pH near 4.0. During the steeping process, about 6% of the dry weight is dissolved, which is then evaporated to condense the steepwater into corn steep liquor. (Corn Products International, 2009.) The remaining insoluble corn kernel is then further processed to produce many products used in foods, livestock feeds and fertilizers.