distillers’ dried grains (DDG) is an industry term for distilling waste that has been dried for use as animal feed. When cooked fermented grain mash passes through a column still, it leaves behind spent grains (also called whole or thick stillage): protein-rich, starch-depleted grain and yeast residues. Fed to livestock, these residues are a source of easily digestible amino acids (protein), fat, and minerals. Early whisky makers often maintained feedlots or sold their residues to local farmers as a side business. Today, these residues are typically dried and then processed into animal feed. After exiting the column still as a slurry depleted of alcohol, the mass passes through a centrifuge that separates solid and liquid components. The resulting liquid (called thin stillage) is concentrated in evaporators, then mixed back with the previously removed solids (called wet cake) and dried, generally using heat. This mixture is known as distillers’ dried grains with solubles (DDGS). As in the past, this co-product of distillation is an additional income source. Drying reduces handling costs and spoilage, making distant and export sales lucrative, since volumes by weight roughly equal those of the alcohol produced from the original grain.
Experienced distillers carefully monitor the color and aroma of their distillers’ dried grains, which should be sweet and golden caramel in color. Changes in color or aroma alert them to the possibility of overheating during drying, which upsets the nutrient balance, or of incomplete fermentation, which in turn results in lower outputs of alcohol.
Jacques, K. A., T. P. Lyons, and D. R. Kelsall. The Alcohol Textbook, 4th ed. Nottingham: Nottingham University Press, 2003.
By: Davin de Kergommeaux