Ethanol Co-Products

Distillers Grains

In addition to producing fuel, the ethanol industry also helps to feed the world. Many feed products can result from the various ethanol production processes. In fact, more grain is available for feed and food use today than at any other time in history.

Continue reading and follow these links to learn more about how the ethanol industry is feeding and fueling the world:


Co-Products of the Dry Milling Industry

Corn is about two-thirds starch, which is converted to ethanol and carbon dioxide during a distilling and fermentation process. The remaining nutrients in corn, such as protein, fat, minerals and vitamins, are concentrated in three different ways and end up as distillers grains or condensed distillers solubles. Distillers grains are a co-product of the dry mill process used to make ethanol from corn.

DDGs-feeding cattle2

Corn distillers grains contain the remaining nutrients after the corn starch is fermented to alcohol. The distillers grains can be sold wet or dried. When distillers grains are dried they lose some energy value compared to wet products. Dried distillers grains and dried distillers grains with solubles are marketed widely around the world as a feed commodity.

Corn distillers dried grains (DDG) is obtained after the removal of ethyl alcohol by distillation from the yeast fermentation of a grain or a grain mixture by separating the resultant coarse grain faction of the whole stillage and drying it by methods employed in the grain distilling industry.

Corn distillers dried grains with solubles (DDGS) are recovered in the distillery and contain all the nutrients from the incoming corn minus the starch. Thus, the DDGS has at least threefold the nutrients as the incoming grain. Since the stillage is recycled, the ratio of these more valuable amino acid types continues to increase so that eventually they represent approximately 16% of the final DDGS’s amino acid content. No other feed ingredient results from such a great percentage of microbial products and their back stocking. DDGS typically analyzes at 27% protein, 11% fat and 9% fiber.

Corn oil can be produced at corn ethanol plants by extracting the oil from the thin stillage portion of the DDGS production process. Corn oil extraction from thin stillage occurs after fermentation and distillation, and before the drying to produce DDGS. Corn oil extraction systems have been added to existing ethanol plants to increase the energy efficiency of production facilities, as well as increase the total amount of fuel that is produced per metric ton of corn processed. Corn oil can then, in turn, be used to produce a very low carbon biodiesel without negatively impacting ethanol production volumes. Several different corn oil extraction technologies are available to the ethanol industry.

Corn Condensed Distiller’s Solubules (CDS) is a term generally used to refer to the evaporated co-products of the grain fermentation industry. The water and solids remaining after distillation of ethanol are called whole stillage. Whole stillage is primarily comprised of water, fiber, protein, and fat. This mixture is centrifuged to separate coarse solids from liquid. The liquid, referref to as thin stillage, goes through an evaporator to remove additional moisture resulting in condensed distiller’s solubles (syrup) which contains approximately 30% dry matter. Condensed distillers solubles can be sold locally to cattle feeders or combined with the coarse solids fraction and dried to produce dried distiller’s grains.

Wet distillers grains (WDG) can be sold as livestock feed or dried into distillers grains (DDG). If syrup is added to wet distillers grains and dried, the resulting product is referred to as distillers dried gains with solubles (DDGS).

De-oiled distillers grains is gaining popularity among ethanol producers as they continue their comittment to removing corn oil. Removing corn oil from the kernel reduces DDGS yield and alters its nutritional profile by primarily reducing the fat and energy content, and increasing the protein concentration.

Co-Products of the Wet Milling Industry

Wet-milling produces four major co-products for the feed industry from the isolated steep water, bran, germ meal and gluten. Together these co-products represent about 25%-30% of the corn processed.

Condensed corn fermented extractives or corn steep liquor is a high-energy liquid feed ingredient. The protein value analyzes at 25% on a 50% solids basis. This product is sometimes combined with the corn gluten feed or may be sold as a pellet binder and is a source of B-vitamins and minerals. corn field-1

Corn germ meal is golden-yellow and is mainly gluten, the high-protein portion of the corn kernel. Corn gluten meal typically analyzes at 20% protein, 2% fat and 9.5% fiber. It has an amino acid balance that makes it valuable in poultry and swine rations. It is also used as a carrier of liquid feed nutrients.

Corn gluten feed is an intermediate protein product that is rich in highly digestible fiber. It may or may not contain the condensed corn extractives. This product is sold as wet or dry. The bran and condensed extractives (sometimes germ meal) are combined and dried in a rotary dryer. The dried corn gluten feed is made into pellets to facilitate handling. It analyzes typically as 21% protein, 2.5% fat and 8% fiber. Wet corn gluten feed (45% dry matter) is similarly combined but not dried. It is a perishable product in 6-10 days and must be fed or stored in an anaerobic environment. These feeds are widely used in complete feeds for dairy and beef cattle, poultry, swine and pets.

Corn gluten meal is a high-protein concentrate typically supplied at 60% protein, 2.5% fat and 1% fiber. It is a valuable source of methionine. Corn gluten meal also has a level of xanthophylls, which offers the poultry feed formulators an efficient yellow pigmenting ingredient. Corn gluten meal also is excellent cattle feed providing a high level of rumen bypass protein.


New Generation Co-Products

Renewable fuels refineries are constantly seeking improvements in operating efficiency, product diversification and innovative measures to take them to the next level of value-added processing.  This new generation of technology is improving the bottom line, reducing energy inputs, and opening doors for new co-products.

Corn Oil ExtractionEthanol-CornOil

Oil extraction technologies have become widely adopted with more than 85% of existing dry mills extracting corn distiller’s oil (CDO). In this process, approximately one-third of the corn oil is removed from thin stillage prior to producing a “reduced-oil” DDGS. The resulting DDGS from this process contains 7 to 9 percent crude fat, and has slightly more crude protein and fiber than DDGS produced without oil extraction.

Corn Fractionation

Increasing ethanol production from a single bushel of corn is now being done by separating the corn kernel into its various components instead of grinding the entire kernel.  Additional starch from the endosperm is available through this method for fermenting into ethanol.  Corn germ, corn bran, “high-protein DDGS” and other value-added products are produced as feed ingredients. These advancements also reduce refinery energy inputs and emissions.

Renewable Processing Power 

High natural gas prices are forcing renewable fuels refineries to look for creative energy sources to provide heat, steam and electricity.  One novel approach is to burn the syrup from the refinery process in a fluidized bed reactor to generate heat and steam.  Using syrup as an energy source reduces natural gas usage by 60% and cuts down on dryer use by up to 50%.  Consideration is being given to pelletizing the ash from the fluidized bed reactor for use as a commercial fertilizer.


Average Nutritional Profile of DDGS

One of the challenges of using corn DDGS in animal feeds is to know the nutrient content and digestibility of the source being fed. Several studies have described variability in nutrient content and digestibility for various animal species (Spiehs et al., 2002; Tjardes and Wright, 2002; Waldroup et al., 2007; Stein and Shurson, 2009) and it is well documented that the nutrient content of corn DDGS can vary among U.S. DDGS sources (see table below), and has been shown to vary overtime within plants (Spiehs et al., 2009).¹

Averages and ranges in composition of selected nutrients (100% dry matter basis) among 32 U.S. corn DDGS sources.² 
Nutrient   Average (CV)   Range
Crude Protein, %   30.9 (4.7)   28.7 – 32.9
Crude Fat, %   10.7 (16.4)   8.8 – 12.4
Crude Fiber, %   7.2 (18.0)   5.4 – 10.4
Ash, %   6.0 (26.6)   3.0 – 9.8
Calculated ME (swine), kcal/kg   3810 (3.5)   3504 – 4048
Lysine, %   0.90 (11.4)   0.61 – 1.06
Arginine, %   1.31 (7.4)   1.01 – 1.48
Tryptophan, %   0.24 (13.7)   0.18 – 0.28
Methionine, %   0.65 (8.4)   0.54 – 0.76
Phosphorus, %   0.75 (19.4)   0.42 – 0.99

Nutritionists want consistency and predictability of nutrient content and digestibility in the feed ingredients they purchase and use. As shown in the table above, the nutrients most variable among DDGS sources are fat, fiber, ash, lysine, tryptophan, and phosphorus. With some ethanol plants using front-end fractionation and back-end oil extraction technologies, the nutrient composition of distiller’s co-products is becoming more diverse and confusing because the term “DDGS” is often misused when describing these nutritionally different corn co-products that are becoming available in the feed ingredient market (e.g. high protein DDGS). As a result, DDGS is less of a “commodity” compared to other feed ingredients such as corn and soybean meal.¹

1. “A Guide to Distiller’s Grains with Solubles (DDGS)”. 2012. U.S. Grains Council.