**2. Production of distiller grain in ethanol plant**

There are two main distillery processes, dry-milling and wet-milling distillery. The dry-milling process is the main process for producing ethanol [4]. The dry-milling process includes primarily the follow steps: grinding or milling, liquefaction, saccharification, fermentation and distillation [5]. The grain is ground to produce bran-free flour, and then mixed with water and enzymes (amylases) to produce a mash (liquefaction). The saccharification is conducted by adding enzymes to the mash to transform starch into dextrose. After saccharification, yeast is added to start the fermentation process to produce a 'beer' and CO2 . The beer is separated through a continuous distillation column to yield alcohol [5]. The remaining material is called whole stillage and consists of all the components of the original grain (except the starch), yeast and added water. The whole stillage is centrifuged to produce wet distiller grain (solid fraction) and thin stillage (liquid fraction). The wet distiller grain contains 30–35% dry matter, while thin stillage has only 5–7% solids. The thin stillage is concentrated through evaporation into condensed distiller solubles, which are mixed with wet distiller grain and dried to become dried distiller grains with solubles, which are the most produced co-products from bioethanol plants. In general, from each tonne of wheat grain, ethanol production results in approximately 365 l of ethanol, 290 kg of CO2 and 290 kg of distiller grain. With continuing changes of technologies in ethanol plants, it should be noted that wheat distiller grain are still evolving, thus the composition and feed value of distiller grain are changing.
