A process of producing ethanol from whole stillage, includes obtaining a supply of whole stillage from an ethanol production facility after ethanol has been extracted therefrom; pre-treating the whole stillage to convert hemicellulose portions of the whole stillage into sugars; adding enzymes to the whole stillage to convert cellulose portions of the whole stillage to sugars; fermenting the whole stillage to create a beer mixture; and distilling the beer mixture to separate ethanol therefrom. The pre-treating step may include adding acid to the whole stillage to decrease its pH level; heating and pressurizing the whole stillage; holding the whole stillage under pressure and heat for a dwell time; removing pressure from the whole stillage to cause flashing; and cooling the whole stillage before the enzymes are added.