The process of producing ethanol from agriculture

Even people outside of production agriculture have likely heard of ethanol before, especially when it comes to corn. But few probably know what is it exactly and how is it made?

Ethanol, a renewable biofuel, plays a significant role in reducing greenhouse gas emissions (U.S. corn ethanol has 44 percent to 52 percent lower GHG emissions than gasoline, according to the Department of Energy) and decreasing reliance on fossil fuels. Derived primarily from agricultural products, ethanol production supports farmers by creating additional markets for their crops, particularly corn. This process not only benefits rural economies but also contributes to energy independence.

Here’s a closer look at how ethanol is produced from agriculture, from crop cultivation to fuel distribution:

1. Feedstock selection and cultivation

The production of ethanol begins with the selection of feedstock, the raw material used in the process. In the United States, corn is the predominant feedstock due to its abundance and high starch content. However, in other regions, crops such as sugarcane, wheat, barley, and sorghum are used. Cellulosic feedstocks, which include agricultural residues (corn stover, wheat straw), wood chips, and dedicated energy crops like switchgrass, are also emerging as sustainable alternatives.

Farmers cultivate these crops specifically for ethanol production or as part of a diversified farming operation. Corn, for example, grows in the Midwest’s nutrient-rich soils and is harvested in late summer or early fall. Once harvested, the corn is transported to ethanol production facilities, marking the beginning of the transformation process.

2. Milling and starch conversion

At the ethanol plant, the feedstock undergoes milling, where corn kernels are ground into fine powder. This step breaks down the material, increasing the surface area for enzymatic action. There are two primary milling processes:

• Dry milling — The most common method, where the entire kernel is ground, and the resulting flour is mixed with water to create a slurry.
• Wet milling — A more complex process that separates the kernel into its components (starch, fiber, germ, and protein) before fermentation.

In dry milling, enzymes are added to the slurry to convert starch into simple sugars, primarily glucose. This process, known as liquefaction, heats the mixture to break down the starch molecules. Following this, a second enzyme facilitates saccharification, converting liquefied starch into fermentable sugars.

3. Fermentation

Fermentation is the heart of ethanol production. Yeast, typically Saccharomyces cerevisiae, is introduced to the sugar-rich solution. The yeast metabolizes the sugars, producing ethanol and carbon dioxide as byproducts. This step takes 48 to 72 hours, during which the mixture, known as mash, is kept in fermentation tanks under controlled conditions to maximize ethanol yield.

4. Distillation and dehydration

Once fermentation is complete, the resulting product, known as “beer,” contains about 10 percent to 15 percent ethanol by volume. To concentrate the ethanol, the mash undergoes distillation. In this process, the mash is heated, and ethanol, which has a lower boiling point than water, evaporates and is collected.

However, distillation alone does not produce fuel-grade ethanol. The remaining water is removed through molecular sieves in a process called dehydration. The final product is nearly pure ethanol (around 99.5 percent).

5. Co-products and waste utilization

Ethanol production generates valuable co-products, reducing waste and enhancing economic viability. One key co-product is distillers grains, a nutrient-rich material used as livestock feed. Carbon dioxide released during fermentation is often captured and sold to industries that require it for carbonated beverages or dry ice production.

In cellulosic ethanol production, leftover biomass can be converted into biogas or used to generate heat and electricity, further reducing the plant’s environmental footprint.

6. Blending and distribution

The ethanol is blended with gasoline at varying concentrations, typically 10 percent (E10) or 15 percent (E15). Higher blends, such as E85, are available for flex-fuel vehicles. After blending, the ethanol is distributed to fuel stations across the country.

Ethanol production from agriculture is a prime example of how farming can intersect with renewable energy. This process not only creates economic opportunities for farmers but also supports sustainability efforts by reducing carbon emissions and promoting cleaner fuel alternatives.

As technology advances, ethanol production is expected to become even more efficient, with increased use of non-food-based feedstocks and improved refining methods, paving the way for a greener energy future.

Michelle Miller, the Farm Babe, is a farmer, public speaker, and writer who has worked for years with row crops, beef cattle, and sheep. She believes education is key in bridging the gap between farmers and consumers.