An Example of Beneficial Microbes: Fuel Ethanol Production from Corn by Yeast

Greg Pryor, 2007. Francis Marion University

Concerns about rising fuel prices, availability (and dependency upon) foreign oil, and global warming resulting from the burning of fossil fuels have all prompted a tremendous recent interest in alternative fuel technologies. In my fuel ethanol research program at FMU, I am conducting a feasibility study on the conversion of locally-grown agricultural crops into an ethanol-based automotive energy source, E85.

E85 is a blend of 85% ethanol and 15% gasoline. This fuel can be used in all "flex-fuel" model cars and many cars produced in 2007, including most minivans, many sedans, and even some pickup trucks (e.g., models include the Caravan, Crown Victoria, Grand Marquis, Town Car, F-150, and others). As reported by many consumers, there is an increase in horsepower but a decrease in mileage (by 2 or 3 mpg) when running on E85, compared to regular gasoline. Before fueling up, however, check your owner's manual or the manufacturer's website to see if your car can run safely on this fuel!

Let me explain how to make E85 in the lab using fairly simple techniques. For starch-based crops, such as corn, the corn kernels are first wetted and allowed to germinate for several days. During this time, natural enzymes in the corn embryo convert the starches into sugars, which can then be fermented by yeast (Saccharomyces cerevisiae) into ethanol. The now "malted" corn is ground into a fine power, heated at a certain temperature for a certain period of time, and then cooled. Yeasts are added to the malted corn solution and fermentation proceeds for several more days. But the process is not done yet; the solution contains less than 10% ethanol, which must be concentrated by distillation.

In the United States, distillation of any alcohol is illegal unless it is covered by a government-issued permit. Distillation of fuel ethanol is no exception. Thus, I applied for a fuel ethanol production permit (through the Alcohol and Tobacco Tax and Trade Bureau; under 26 U.S.C. 5181), which was approved several months later, following a phone interview and a background check. I then bought a commercially-available stainless steel still that can process several gallons of mash (fermented corn solution) at a time. It is a reflux still that stands over 6 feet high, has a packed vertical column and water-cooling mechanisms, and produces a single-run distillate of around 95-96% ethanol (190+ proof). In contrast, the old-time "pot stills" used by moonshiners and introductory chemistry lab students produce a significantly less-concentrated distillate.

From this point, all water needs to be removed from the distillate. This cannot be achieved by further, simple distillation because of the azeotropic nature of an alcohol-water mixture. Therefore, a water-absorbing solid substance (ex. zeolite, a "molecular sieve") is added to the distillate and the water is removed from the solution. The essentially-pure ethanol is then combined with gasoline in the ratio 85:15, to make E85.

The bottom line on E85 is that it promises to reduce our dependency on oil-based fuels, and it is environmentally friendly, compared to gasoline. Gasoline is derived from underground petroleum deposits, so when it is burned, there is a net gain of carbon dioxide (CO₂) in the atmosphere. Elevated CO₂ levels are associated with global warming and other environmental problems. Burning pure corn-based ethanol, however, results in no net gain of CO₂ in the atmosphere because the same amount of carbon dioxide was used by the plants that it came from. Burning E85 results in a net gain of CO₂ but it is significantly less than that from burning gasoline.

The idea of using ethanol as a fuel is not a new one; in fact, Henry Ford intended his cars (the first American automobiles) to run on homegrown and locally-produced ethanol fuel. In 1925, Ford told the New York Times that ethanol was the fuel of the future. He obviously appreciated the phenomenon of microbial fermentation. "There is fuel in every bit of vegetable matter that can be fermented," he said, "there's enough alcohol in one year's yield of an acre of potatoes to drive the machinery necessary to cultivate the fields for a hundred years." It has been a long and winding road from the first ethanol-powered Model T Ford to the 2007 flex-fuel Ford F-150 pickup, but in some ways, some things never seem to change.

Reference: "Ford Predicts Fuel from Vegetation," New York Times, Sept. 20, 1925, p. 24.