**4. Importance of Coproducts**

Coproducts are important to the ethanol industry for a number of reasons. First and foremost, coproducts are additional sources of revenue to ethanol plants. Since these coproducts are primarily used as animal feed ingredients, monitoring and maintaining the consistency of coproduct compositions is critical to sales and utilization. DDGS from most modern U.S. fuel ethanol plants typically contains about 30% protein, 10% fat, at least 40% neutral detergent fibre, and up to 12% starch (of course, the lower the starch the better, as this is indicative of conversion efficiency) [19, 20]. DDGS composition can vary somewhat between plants. Within a single plant over time, however, DDGS is much less variable than amongst plants. Table 1 illustrates composition of DDGS from five ethanol plants in South Dakota, USA. Protein levels ranged from 28.3 to 31.8%, fat ranged between 9.4 and 11.0%, and ash ranged from 4.1 to 13.3%.


**Table 1.** Composition (% db) of DDGS from ethanol plants in South Dakota [21].

**Figure 5.** Flow chart of typical corn dry grind fuel ethanol and coproducts processing operations.

86 Biofuels - Status and Perspective

It is instructive to examine composition differences in DDGS from plants throughout the U.S. For example, DDGS from 49 plants from 12 states were analysed for proximate composition (Table 2) and amino acid profiles (Table 3) [22]. On average, dry matter ranged from 87.9% to 90.6%, protein ranged from 29.4% to 32.6%, fat ranged from 9.6% to 12.8%, crude fibre ranged from 6.7% to 9.3%, and ash ranged from 4.2% to 6.6%. It appeared that geographic location of the ethanol plants didn't really play a role for any of the nutrients, as no nutrients seemed to be significantly affected by location.

Some ethanol plants are implementing new fractionation systems to produce new coproduct streams [13], and this is beginning to alter the nutrient composition of the distillers coproducts in the market place. More will be discussed later in this chapter.


**Table 2.** Typical proximate composition (% db) of DDGS (averages of samples from 49 ethanol plants) [22].



90.6%, protein ranged from 29.4% to 32.6%, fat ranged from 9.6% to 12.8%, crude fibre ranged from 6.7% to 9.3%, and ash ranged from 4.2% to 6.6%. It appeared that geographic location of the ethanol plants didn't really play a role for any of the nutrients, as no nutrients seemed to

Some ethanol plants are implementing new fractionation systems to produce new coproduct streams [13], and this is beginning to alter the nutrient composition of the distillers coproducts

Minnesota 12 89.03 30.70 11.73 6.96 6.63 Illinois 6 89.72 29.98 11.48 7.26 5.60 Indiana 2 90.55 29.40 12.80 8.07 5.86 Iowa 7 88.92 31.23 10.27 7.57 5.76 Kentucky 3 90.57 29.43 9.77 9.28 4.47 Michigan 1 89.60 32.60 11.00 7.37 6.06 Missouri 2 87.90 30.45 10.25 7.17 5.39 Nebraska 4 89.02 30.40 11.35 8.13 4.23 New York 1 88.21 30.00 9.60 7.87 4.55 North Dakota 4 89.21 31.75 11.70 6.89 6.32 South Dakota 4 88.61 31.80 11.53 6.65 4.78 Wisconsin 3 89.68 31.70 11.63 7.59 5.77 Overall Average 49 (Total) 89.25 30.79 11.09 7.57 5.45

**Table 2.** Typical proximate composition (% db) of DDGS (averages of samples from 49 ethanol plants) [22].

**Histidine (%)**

Minnesota 12 1.39 0.84 1.20 3.63 0.99 0.61 Illinois 6 1.37 0.82 1.15 3.45 0.94 0.63 Indiana 2 1.19 0.79 1.08 3.28 0.85 0.60 Iowa 7 1.34 0.86 1.20 3.63 0.95 0.61 Kentucky 3 1.35 0.79 1.09 3.33 0.89 0.66 Michigan 1 1.28 0.86 1.18 3.67 0.87 0.71 Missouri 2 1.35 0.83 1.18 3.68 0.89 0.73 Nebraska 4 1.46 0.88 1.18 3.61 1.05 0.65 New York 1 1.46 0.85 1.21 3.64 1.04 0.61 North Dakota 4 1.37 0.88 1.24 3.76 0.97 0.65

**Isoleucine (%)**

**Leucine (%)**

**Lysine (%)**

**Methionine (%)**

**Crude Protein (%)**

**Crude Lipid (%)**

**Crude Fibre (%)**

**Ash (%)**

in the market place. More will be discussed later in this chapter.

**(%)**

be significantly affected by location.

88 Biofuels - Status and Perspective

**State**

**Plants Sampled** **Arginine (%)**

**State Plants Sampled Dry Matter**

**Table 3.** Typical amino acid levels (% db) of DDGS (averages of samples from 49 ethanol plants) [22].

The U.S. ethanol industry's primary market for distillers grains has historically been as a commodity livestock feed ingredient. Most often this has been in the form of DDGS, and in recent years in the form of DWG. All other ethanol coproducts have historically been sold at much lower levels; some of these other coproducts are not produced at some ethanol plants). Using ethanol coproducts for livestock feed or feed supplements have become effective methods for using these materials. Coproducts contain appropriate nutrients and they are highly digestible (depending on the species). Furthermore, use of coproducts in animal feeds (in place of corn grain) will actually help offset corn which has been used for ethanol produc‐ tion (the so-called food vs. fuel debate). In fact, it has been shown that DDGS can replace corn in livestock diets on a 1:1 up to a 1:1.2 level, depending on the species. The majority (over 80%) of U.S. distillers coproducts are used in beef and dairy feeds, because ruminants can use high levels of fibre. As feed ingredient prices have increased in recent years, coupled with increasing knowledge about how to effectively use these feed ingredients, ethanol coproduct use in swine and poultry diets have increased in recent years [22]. Many feeding trials have been conducted on coproducts in livestock diets over the years, for both monogastric and ruminant feeds (many of these studies are fully described in Liu and Rosentrater, 2011). Depending on the diet composition used, all livestock species have been shown to thrive at 10% DDGS inclusion, and most can tolerate levels up to and even greater than 20%.

DDGS use in livestock diets has continued to increase over the years. Various predictions of peak potential DDGS use in domestic U.S. beef, dairy, swine, and poultry markets have estimated that between 40 and 60 million t could be used in the U.S. each year, depending upon inclusion rates, age, etc., for each species [23, 24, 25]. Around the world, the need for protein-based animal feeds continues to grow, and DDGS has become a global commodity. Of the 23 million t of DDGS produced in 2008 [13], 4.5 million t were exported to international markets [26]; this accounted for nearly 20% of U.S. DDGS production that year (Figure 6). And the potential for global exports is projected to increase for the foreseeable future, and will likely hover near about 25% of all DDGS production in coming years [25, 27]. In recent years, China has become the dominant global importer of DDGS. Extensive information about the use of DDGS in livestock diets can be found in [18] as well as [28].

8 **Figure 6.** A. DDGS exports from the U.S. over time. B. Countries who imported DDGS from the U.S. in 2008, 2010, 2012 (adapted from [27, 29]).

Fig. 6. A. DDGS exports from the U.S. over time. B. Countries who imported DDGS from the U.S. in 2008, 2010,

2012 (adapted from [27, 29]).

The sale of nonfermentable coproducts is critical to the fuel ethanol industry as a source of revenue; and these materials have also become important feed ingredients to the livestock industry over the last decade. Sales of dry and wet distillers coproducts generally translates into 10 to 20% of an ethanol plant's total revenues, and can even be as high as 40% (depending on the economics). These materials really are "coproducts", not "byproducts" or "waste materials". In fact, many plants recognize this and promote their simultaneous production of animal feed and biofuel.

composition used, all livestock species have been shown to thrive at 10% DDGS inclusion, and

DDGS use in livestock diets has continued to increase over the years. Various predictions of peak potential DDGS use in domestic U.S. beef, dairy, swine, and poultry markets have estimated that between 40 and 60 million t could be used in the U.S. each year, depending upon inclusion rates, age, etc., for each species [23, 24, 25]. Around the world, the need for protein-based animal feeds continues to grow, and DDGS has become a global commodity. Of the 23 million t of DDGS produced in 2008 [13], 4.5 million t were exported to international markets [26]; this accounted for nearly 20% of U.S. DDGS production that year (Figure 6). And the potential for global exports is projected to increase for the foreseeable future, and will likely hover near about 25% of all DDGS production in coming years [25, 27]. In recent years, China has become the dominant global importer of DDGS. Extensive information about the use of

8

**Figure 6.** A. DDGS exports from the U.S. over time. B. Countries who imported DDGS from the U.S. in 2008, 2010, 2012

Fig. 6. A. DDGS exports from the U.S. over time. B. Countries who imported DDGS from the U.S. in 2008, 2010,

most can tolerate levels up to and even greater than 20%.

90 Biofuels - Status and Perspective

DDGS in livestock diets can be found in [18] as well as [28].

A

2012 (adapted from [27, 29]).

(adapted from [27, 29]).

**DDGS (tonnes) x 106**

1992/93

1993/94

1994/95

1995/96

1996/97

1997/98

1998/99

1999/00

Production Export

2000/01

2001/02

**Marketing year**

2002/03

2003/04

2004/05

2005/06

2006/07

2007/08

2008/09

2009/10

B

2010/11

In recent years, the market price of DDGS has ranged from approximately \$50/t (in the early 2000s) to more than \$300/t (2012-2013) (Figure 7). The prices of corn and DDGS have generally paralleled each other fairly well over the years (Figure 8A). This trend occurs due, in large part, to the fact that DDGS is often used to replace corn in livestock diets. In the last decade, DDGS has increasingly been used as a soybean meal replacement also. Because soybean meal has a higher protein content, DDGS is often sold at a lower price compared to either corn or soybean meal (Figure 8A). This has been true volumetrically as well as per unit protein (Figure 8B). In the last few years DDGS has actually been sold at more than 100% the value of corn. This is frequently due to external impacts on the marketplace, including international exports.

**Figure 7.** DDGS sales price over time (monthly averages) (adapted from [16, 30]).

Fig. 8. A. Example comparisons of DDGS, soybean meal (SBM), and corn sales prices and their relative comparisons. B. Cost comparisons on a per unit protein basis (adapted from [30]). **Figure 8.** A. Example comparisons of DDGS, soybean meal (SBM), and corn sales prices and their relative comparisons. B. Cost comparisons on a per unit protein basis (adapted from [30]).

### **5. Coproduct Evolution**

10 Even though the corn ethanol industry is maturing, there continue to be efforts to develop new, valued-added materials from the corn kernels as well as from the coproduct materials. When these research efforts are commercialised, they will result in more products from the corn kernel itself (an approach known as upstream fractionation) and the distillers grains (known as downstream fractionation). These types of fractionation approaches can result in the separation of components of high, medium, and low value (Figure 9). For example, several mechanical and chemical approaches have been developed to remove protein, fibre, or oil components from the endosperm (which contains the starch). This type of separation will allow a highly-concentrated starch substrate to be introduced to the fermentation process, and will allow the other corn kernel components to be used for human food or other high-value applications. [31] provided an extensive discussion regarding various pre-fermentation fractionation approaches. On the other hand, post-fermentation fractionation techniques have also been examined. For example, [32] used a combination of air classification and sieving to separate fibre particles from DDGS. All of these approaches, if implemented commercially, will alter the chemical composition and digestibility of the resulting DDGS.

Many plants have recently begun adding capabilities to concentrate nutrient streams such as oil, protein, and fibre into specific fractions, which can then be used for targeted markets and specific uses. For example, one company in Iowa is now separating fibre from the DDGS and using it as a feedstock for cellulosic ethanol production. Additionally, many companies have begun removing oil from the whole stillage and/or CDS streams (Figure 10). This oil, which is officially known as Distillers Oil, Feed Grade (Figure 11), can readily be converted into biodiesel or animal feed ingredients, but they cannot be used for food grade corn oil, because they are too degraded. In fact, more than 85% of U.S. ethanol plants are now removing oil, because the economics are so favourable. Of note, in 2010 almost no ethanol plants were extracting oil...the rapid increase has solely been due to added value streams for the ethanol plants. On the horizon is concentrated corn proteins, which can be used for high-value animal feeds (such as aquaculture or pet foods), or other feed applications which require high protein levels (such as monogastrics or younger animals).

**Figure 9.** Fractionation of DDGS into individual chemical components (or at least concentrating them) offers the op‐ portunity for new value-added uses and new revenue streams.

10

Even though the corn ethanol industry is maturing, there continue to be efforts to develop new, valued-added materials from the corn kernels as well as from the coproduct materials. When these research efforts are commercialised, they will result in more products from the corn kernel itself (an approach known as upstream fractionation) and the distillers grains (known as downstream fractionation). These types of fractionation approaches can result in

Fig. 8. A. Example comparisons of DDGS, soybean meal (SBM), and corn sales prices and their relative comparisons.

**Figure 8.** A. Example comparisons of DDGS, soybean meal (SBM), and corn sales prices and their relative comparisons.

B. Cost comparisons on a per unit protein basis (adapted from [30]).

B. Cost comparisons on a per unit protein basis (adapted from [30]).

**5. Coproduct Evolution**

A

92 Biofuels - Status and Perspective

B

**Figure 10.** Oil is now removed at many ethanol plants via centrifugation of condensed distillers solubles, after a heat‐ ing step and additional chemicals are added, which allow the oil to be removed without forming an emulsion.

**Figure 11.** Distillers Oil, Feed Grade, is being extracted from nearly 85% of all U.S. ethanol plants in 2014 (Photo cour‐ tesy of Rosentrater).

As these process modifications are developed, tested, and implemented at commercial facilities, improvements in coproducts will be realized and increasingly used in the market‐ place. These new products will require extensive investigation in order to determine how to optimally use them and to quantify their values in the marketplace.
