DDG (distiller’s dried grains) is a valuable co-product of the dry-grind fuel ethanol industry, which generates ethanol from corn and/or spent grain. DDG is further processed to produce DDGS, (distiller’s dried grains with solubles), which is high in energy protein, fat, minerals and vitamins, making DDGS an attractive, lower-cost alternative to traditional livestock and poultry feed ingredients. As a component of a properly formulated feed, DDGS contributes to excellent animal health and food product quality, making it one of the most popular animal feed ingredients worldwide.
Ground corn is fermented through the addition of water, enzymes and yeast. Fuel ethanol is distilled from the mash, leaving spent mash (stillage) to be separated into a solid and aqueous faction. The liquid, commonly termed ‘thin stillage,’ is reduced to a nutrient-rich syrup known as condensed distillers solubles. Addition of this syrup to the solid faction with further drying results in the formation of DDGS.
Fermentation process- Corn is ground into a coarse flour, to which a water and enzyme mix is added. The enzymes break the starch down into sugar, turning the mix into a mash that is heated then cooled before the addition of yeast. This causes the sugar to ferment, producing ethanol, carbon dioxide and other by-products.
Distillation and centrifugation process- The ethanol is distilled from the mash leaving spent mash or whole stillage, which is composed of water, fat, protein and fiber. It is then separated into a solid and liquid faction through press screens or centrifugation
Evaporation process- The liquid (or thin stillage) goes through an evaporator to remove additional moisture, resulting in condensed distiller’s solubles which are 30 percent dry matter by weight.
Combination process- The solids (or wet cake) resulting from centrifugation contain about 35% dry matter. These are mixed with condensed distiller’s solubles and dried to produce distiller’s dried grains with solubles (also known as DDGS, which is 88% dry matter).
Online near infrared moisture measurement provides the means to optimize the drying operation. The target moisture content is 10–12%. The closer to 12%, the greater the product yield and profitability whilst still maintaining a sufficiently low enough moisture content to prevent spoilage during transportation and storage.
Measurement is typically made post-dryer, such that the dryer temperature or load can be controlled through a feed-back control loop. The gauge can be installed over an open conveyor or at the end of a screw conveyor, provided the flights do not interfere with the Near Infrared beam.
The moisture content of DDGS impacts the profitability of the production facility, as tightly controlled dryer costs and wastage are reduced and product yield increases.
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