Let's make dried distillers grains (DDGS)

DDGS production: the first steps

Dried distillers grains are a coproduct from ethanol production from grains such as corn, rice, soy, wheat, etc. Shortly known as DDGS, the grains are used as protein-rich animal feed for cattle, dairy cows, swine, and some poultry. Grain received in the factory contains foreign materials like dust, straw, and stem residues which must be cleaned before storing in silos and further processing.

The debris is cleaned with the help of equipment such as a pre-cleaner, de-stoner, and magnetic separator. Once the grains are cleaned, they are ground into a powder using a hammer mill or a roller mill. The mixture of ground grains, water, and amylolytic enzymes to hydrolyze starch into glucose is cooked at 40–60°C in the pre-mixing tank. The slurry is passed through a jet cooker where the temperature is maintained at 110 to 120°C, and finally, the process is finished in the liquefaction tank at 90°C. During this process, the long chains of starch are hydrolyzed and broken into smaller chains, increasing the amount of sugars, which lowers viscosity.

The core steps in the production of DDGS

Before starting the fermentation process, the slurry must be cooled down to 32°C. Once the ideal temperature is reached, the DDGS production process is ready for the core step – fermentation. In the fermentation tank, the slurry is mixed with water and activated yeast which consumes the sugars in the grains, producing ethanol and carbon dioxide. Depending on the desired alcohol level, the fermentation process can take around two days.

The resulting mixture, beer, is sent to the distillation column, where the alcohol is separated from the water and other impurities, which produces around 95% ethanol by volume. Stillage, the leftover solids, is processed in a centrifuge where the liquid is separated from the wet cake, as the solid bits are called. The liquid is then transformed into syrup in an evaporation tank and added back to the wet cake, which is then sent to the rotary drum drier, where it must be dried down to around 10% moisture content. Before transportation, it must be cooled in storage.

The use and production of wet and dried distillers gains

There are two common types of distillers grains: wet and dry. Wet distillers grains, abbreviated as WDG, contain primarily grain residues of the protein, fiber, and fat after the grain’s starch is converted into ethanol, with up to 70% moisture and only 30% of dry matter. WDG has a shelf life of four to five days. Due to the water content and shelf life, WDG is usually used locally. On the other hand, for longer shelf life, almost indefinite, DDGS are dried to about 10% of moisture and may be shipped to any market regardless of its proximity to an ethanol plant.