Sweet sorghum is an ethanol powerhouse. And, it can conservatively net $613/acre even at $1.55/gal. ethanol, independent agronomists are discovering.

“The profit for growers is a multiple of corn-soybean rotation,”says Michael McNeill, an Algona, IA, crop advisor researching sweet sorghum-based ethanol.

Agronomically, sweet sorghum is low maintenance. Sorghum bicolor (L.) Moench is a drought-resistant grass from Africa. Its sugar production peaks in hot, dry weather and cool nights, and it only needs about 30-50% of corn's nitrogen requirement and few or no herbicides. Its abundant growth crowds out common weeds.

The center part of the plant stalk contains the most sugar-rich juice. This juice enables ethanol producers to skip the first step of converting corn's starch to sugars because the sugars are already there.

The rest of the sweet sorghum plant can be fed to cattle to balance out dried distillers grains (DDGs), or can decompose to return nitrogen, phosphorus and potassium to the soil. Stalks can also be feedstocks for cellulosic ethanol and paper.

In the Corn Belt, sweet sorghum has a 100-day growing season. It's planted when the soil reaches 60° (June 1) using a corn planter equipped with regular sorghum seed plates. Any herbicides, if used, are similar to those used for corn. Some herbicides will require a special product be put on the seed before planting. Harvest is scheduled based on sugar content (around the first or second week of September in northern Iowa). It takes several cool nights for the sugar content to reach optimum levels.

A group of four Iowa crop consultants are intrigued with sweet sorghum's economic and agronomic potential contributions to established corn-soybean rotations. In addition to boosting Corn Belt profitability, sweet sorghum also “makes an ideal third crop to break up the pest and disease cycles of conventional rotations,” says McNeill, owner of Ag Advisory Crop Consultants, Algona, IA. “Sweet sorghum breaks the cycle of soybean cyst nematode and the diapause of northern corn rootworm.”

McNeill and three crop consultants across north-central Iowa who own IDEA (Independent Distributed Energy Alliance) are researching the preliminary agronomics and economics of sweet sorghum-based ethanol. The group has been through two growing/harvest/pressing/fermentation seasons, and is refining harvest, pressing and distillation equipment concepts.

These agronomists envision farmer-owned LLCs that grow and process sweet sorghum into ethanol to supplement their primary corn and soybean enterprises. “Maybe the model will be a cluster of farmers sharing a still,” says Frank Moore, a Cresco, IA, farmer and IDEA crop consultant collaborating with McNeill on this research. “The single biggest challenge at this point is optimizing the equipment. There are a limited number of presses. So we are probably looking at adapting a design that harvests and presses the stalks in one process, and then calculating the best number of acres for the most cost-effective ownership.”

Although Kentucky and Tennessee lead the nation in sweet sorghum syrup production, the largest single sweet sorghum grower is in Pella, IA. Because sweet sorghum can't compete with the economics of sugarcane as a sweetener, it has never matured into a well-developed industry. “You'd be hard pressed to find more than a few pounds of sweet sorghum seed right now,” McNeill says. (His background in plant breeding and research is helpful in developing seed hybrids best suited to Midwestern syrup production, one of the many details necessary to establish a Midwestern sweet sorghum/ethanol industry.)

Another key detail is a shortage of presses needed to squeeze the sugary juice from the stalks. The few in existence date back to the turn of the century when sweet sorghum was grown for its syrup (similar to molasses but more nutritious). Sweet sorghum juice contains about 15-18% sugar and is very high in vitamins and minerals. Today, sweet sorghum juice production occurs more as a tourist attraction, akin to pick-your- own orchards.

One acre of sweet sorghum produces about 5,000 gal. of sweet juice pressed from its stalks. That juice is fermented, then distilled in the field down to about 500-1,000 gal. ethanol/acre. Further refinement is required to bring it up to 200 proof. This process might be done most efficiently at an existing ethanol plant.

Harvesting and pressing the juice in the field makes the most sense since transporting high-moisture stalks to a central facility is unwieldy and costly. And the pressed juice has a limited shelf life before it can be distilled into ethanol. The yeast, which starts the fermentation process, must be added immediately following the extraction of juice from the stalk.

A portable still would enable groups of farmers to share its expense, but the Bureau of Alcohol Tobacco and Firearms regulations on the books from Prohibition forbid portable stills. So IDEA is in the early stages of refining the concept. Yet, the numbers tell them they're onto something.

The Bottom Line

Sweet sorghum-based ethanol returns roughly $400-700/acre net profit, based on $1.55/gal. ethanol.

The IDEA crop consulting group (Independent Distributed Energy Alliance) figures that sweet sorghum conservatively yields 500 gal. ethanol/acre at $1.55/gal., equaling per-acre gross revenue of $775 and net-per-acre revenue of $613. Less conservative assumptions on ethanol yield are 1,000 gal. ethanol/acre at $1.55, earning $1,550/acre gross and $1,388 net return/acre.

Further research will optimize inputs and processing options, but preliminary results are promising. A few other facts about sweet sorghum-based ethanol are:

  • Optimum sugar yield from sweet sorghum results from hot, dry weather, cool nights and 50-75 lbs. nitrogen/acre. One of the greatest sweet sorghum sugar yields of all time was in southern Iowa in 1988 when corn only yielded 24 bu./acre.

  • The best processing option may vary by region, says Dani Bellmer, associate professor, Oklahoma State University Biosystems Engineering, who has researched the profitability of sweet sorghum ethanol. “It has tremendous profit potential,” she says.

  • The sweet sorghum plant can be harvested, processed and stored in similar fashion to silage. Or the juice can be distilled into ethanol that is 70-90% pure, and then transported to an ethanol plant for further distillation to 200-proof alcohol — at a conventional ethanol plant or with molecular sieves.

Two challenges with harvesting and fermenting sweet sorghum's sugars to ethanol are:

  • The mass of the plant, containing 78% water, dictates in-field processing and which type of stalk press to use. A portable still is illegal (alcohol, tobacco and firearms regulations were written during Prohibition and carry stiff penalties).

  • Spoilage. The sugars in the stalk begin to sour at harvest, or can freeze in the field.

See also the Sweet Sorghum Producers and Processors Web site: www.ca.uky.edu/nssppa/ or www.sseassociation.org, the Sweet Sorghum Ethanol Association.