**2. Objectives**

this industry become visible to the average citizen. This has been due, in part, to the growing demand for domestic transportation fuels for national security, escalating prices at the fuel pump, positive economic effects throughout rural America, as well as questions and contro‐ versies surrounding the production and use of corn ethanol. While fuel is the main aim of the ethanol industry, nonfermentable coproducts are also generated during manufacturing. The primary coproduct is distillers dried grains with solubles (DDGS) (Figure 1), which is the focus

**Figure 1.** Corn-based Distillers Dried Grains with Solubles (DDGS) is currently the most common coproduct available

To help meet the increasing demand for transportation fuels, and to meet federal U.S. man‐ dates, the number of ethanol plants has rapidly increased in recent years, as has the quantity of fuel ethanol and coproducts produced (Figure 2). As of 2015, the RFS (Renewable Fuel Standard) mandates the use of 15 billion gal/y (56.8 billion L/y) of corn-based ethanol in the U.S. [13]. At the beginning of 2015, there were 213 fuel ethanol plants in the U.S., which produced nearly 56.8 billion L/y (15.0 billion gal/y) [12, 15]. As the biofuels industry continues

Most new ethanol plants have been dry-grind facilities (Figure 3), which will be discussed subsequently. As production volume has increased, the processing residues, known collec‐ tively as "distillers grains" – have increased concomitantly (Figure 2). Between 35 and 40 million metric tonnes (t) of distillers grains (both wet and dry) will be produced each year by the U.S. fuel ethanol industry over the next several years. In recent years there has actually been a slight decline in distillers grains production, due to evolving processes which now extract oil from the coproduct streams. This will be discussed at a later point in the chapter.

As the industry has grown over the last few decades, the consumption of corn has grown as well (Figure 4). In recent years, over 30% of the U.S. corn crop is used to produce fuel ethanol.

to evolve, cellulosic and other bio-based fuels will gain prevalence in coming years.

from U.S. fuel ethanol plants (Photo courtesy of Rosentrater).

of this chapter.

82 Biofuels - Status and Perspective

The aims of this chapter are multiple: 1) to review fuel ethanol and coproduct manufacturing in the U.S.; 2) to discuss the importance of distillers coproducts to both the biofuel and the livestock industries; and 3) to illustrate how coproducts are changing and potential uses are expanding as the ethanol industry evolves.

**Figure 2.** U.S. fuel ethanol (gal) and DDGS (t) production over time; RFS denotes levels mandated by the Renewable Fuel Standard. Inset shows number of U.S. ethanol plants over time [12, 13, 14, 15].

Fig. 2. U.S. fuel ethanol (gal) and DDGS (t) production over time; RFS denotes levels mandated by the Renewable

Fuel Standard. Inset shows number of U.S. ethanol plants over time [12, 13, 14, 15].

3 Fig. 3. U.S. dry grind corn-to-ethanol manufacturing plants. A. 450 x 106 L/y plant. B. 80 x 106 L/y plant (Photos courtesy of Rosentrater). **Figure 3.** U.S. dry grind corn-to-ethanol manufacturing plants. A. 450 x 106 L/y plant. B. 80 x 106 L/y plant (Photos courtesy of Rosentrater).

**Figure 4.** U.S. corn production (bu) and consumption according to major categories of use (adapted from [16]).
