Distillers dried grains with solubles (DDGS) are an important co-product of the ethanol production process. In this article, we’ll take a look at how DDGS are used, how they contribute to ethanol’s overall sustainability and technological improvements to make them even better.

Distillers dried grains with solubles (DDGS) are an important co-product of the ethanol production process. For producers or users of animal feed, DDGS represent a low-cost feed ingredient rich in energy, protein, and phosphorus.

Meanwhile, for ethanol producers, DDGS are a key portion of their business, especially in lean times. By some estimates, co-products actually contribute up to 23% or more of a producer’s total revenue. And while this contribution to the bottom line is significant, the contribution of DDGS to the sustainability of starch-based ethanol in general is also worth noting.

 

Weighing the pros and cons of traditional DDGS

DDGS contain plenty of the protein, fat, minerals and vitamins that animals need, making them a popular feed ingredient in livestock and poultry diets. In fact, due to the removal of corn-starch during fermentation, the content of these nutrients are three times more concentrated in the DDGS than in the ingoing corn. Compared to traditional ingredients such as corn and soybean meal, DDGS are less expensive and, since they are dried, can be transported over longer distances due to their increased shelf life.

Of course, DDGS is not perfect. As for the nutrients, the fiber content in DDGS is also three times more concentrated than corn, which presents a challenge. Monogastric livestock—or, the portion of livestock that has a one-chambered stomach, including pigs and chickens—find the fiber portion of DDGS difficult to metabolize into usable energy. In other words, they can’t digest it efficiently. Consequently, the inclusion of DDGS in monogastric feed rations is limited, since if it can’t be metabolized, it’s basically just taking up space in the feed.

Take, for example, pigs: Despite the fact that the concentration of energy (combustion energy) in DDGS is greater than that of corn, DDGS’ lower digestibility means there’s no difference in metabolizable energy (energy available to the animal). And so, due to both fiber and fat content, it’s often recommended that pigs be fed diets including only about 20-30% DDGS.

Meanwhile for poultry, it’s only recommended that a diet include up to 15% corn DDGS.

But, for ruminants such as sheep and cows, which digest their food in a four-chambered stomach, DDGS are a more nutritious dietary addition. In fact, the U.S. Grains Council determined corn DDGS to be “an excellent energy and protein source for beef cattle in all phases of production.” They went on to note that they can be effectively used as an energy source and be included as up to 40% of the ration dry matter intake for finishing cattle with excellent growth performance and meat quality.

It’s a similar story in regards to dairy cows. The U.S. Grains Council also found that corn DDGS are a good source of protein, fat, phosphorous and energy for lactating dairy cows. And, when included as 20-30% of dairy cow diets, DDGS support milk production equal to or greater than diets with no DDGS.

 

Developing a cheaper, more nutritious feedstock

This variation in DDGS’ nutritional effectiveness opens up an opportunity for technological advancement—after all, the energy is already there. We just need to find a way to “free it up.”

Several proposed methods exist for unlocking this dietary potential of DDGS, especially for monogastrics. These include both “bolt-on” solutions—from plant equipment to process additions—as well as “drop-in” solutions such as enzymes, which can be added during various points in the dry-grind process.

One method involves corn fractionation prior to the dry-grind process that ethanol plants typically use. In this process, the three different parts of the corn kernel are separated before fermentation. This way, the endosperm fraction, which is high in starch, is the only portion that actually enters fermentation.

The remaining portions can then be processed to extract high value oil or to make other products as needed. The non-fermentable endosperm can be made into high protein DDGS best used by monogastrics. Meanwhile the bran, which is high in fiber, can be made into DDGS specifically for ruminants.

 

Improving DDGS’ nutritional value with enzymes

A second method of improving the nutritional value of DDGS is by using a drop-in solution: enzymes. Enzymes can be added at several points in the dry grind process, including to the liquefaction tanks, the fermentation tanks and the whole stillage tank.

One strategy is to use specific enzymes called xylanases to partially break down the corn’s fiber during Drop-In Solution Diagramprocessing. The DDGS fiber originates from the corn cell wall structure, with arabinoxylan being the major polysaccharide component. Xylanases are enzymes that degrade the arabinoxylan structure. This, in turn, improves the release of nutrients and utilization of fiber from hindgut fermentation in livestock, enabling the animals to extract more energy from their food. A second approach works in a similar way, but on corn protein. Here, enzymes called proteases are used to partially break down the protein, improving overall digestibility, total metabolizable energy and amino acid digestibility.

 

Playing a role in ethanol’s overall sustainability

Co-products represent an important revenue stream for ethanol producers, especially in times such as 2015 when margins were especially small. But by replacing corn and soybeans fed to livestock, DDGS also increase the sustainability of ethanol by reducing its carbon footprint. After all, by developing co-products, a plant’s fossil fuel usage can be spread over a wider variety and value of products, making ethanol production more environmentally viable.

And, while there may be debate about how much credit a producer should receive for producing co-products, it is universally acknowledged that every 1 lb. of DDGS displaces at least 1 lb. of corn. Industry veterans may also recall a debate about whether ethanol production threatens food security (the latest research by the International Food Policy Research Institute says it does not). Though that is no longer a hot topic, valuable co-products like DDGS only strengthen the ethanol industry’s position.

 

Back to Basics is an ongoing series in which Think Bioenergy takes a closer look at a common term or topic in the bioenergy industry. Have an idea for a topic you’d like to see explored? Submit your suggestion in the comments!

Joe Jump

Staff Scientist at Novozymes

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