During the dry milling of corn to produce ethanol, one of the primary coproducts is thin stillage. During grain-based ethanol production, thin stillage is recovered from the whole stillage following centrifugation of the yeast cells. Thin stillage is a substrate that contains a high percentage of glycerol and about 1% nitrogen (Kim et al. 2008, 2010). It is usually mixed
with wet distillers’ grains and dried to produce dried distillers’ grains with solubles (Kim et al. 2008). To reduce electrical costs associated with the drying process, many ethanol plants are marketing wet distillers’ grains (Kim et al. 2008). As a result, thin stillage is becoming a low value co-product although it could serve as a substrate for the production of alcohols or organic acids. While it has been shown that the glycerol present in thin stillage can be utilized by microorganisms to produce ethanol or butanol (Gonzalez et al. 2010; Ahn et al. 2011), the microbial production of an organic acid, such as malic acid, from thin stillage has not been studied.