10 Edible Biofuels

Along with being a staple in the Western diet, corn has turned out to be a very popular biofuel. Thanks to ready availability and its high content of ethanol-producing sugars, this biofuel is familiar to many drivers -- it's often the source of the ethanol in E85 gasoline blends.

Ethanol producers turn corn from food to fuel using a system that first breaks the corn down into its basic components: lignin, a substance that forms and strengthens the plant's cell walls, and cellulose, which contains the plant's sugars. The producers ferment the cellulose to produce ethanol, essentially a high-test version of the types of alcohol produced from corn mash [source: Shakashiri]. The refined fuel ethanol is often blended into gasoline as a smog-reducing agent, but it can be used by itself as a fuel.

In the United States, corn-based ethanol is truly a domestic alternative to some of the nation's foreign fossil fuel use. But it's not without drawbacks. Research suggests that the energy that goes into producing corn ethanol -- from the gas in the tractor on the farm to the fertilizer used to keep the corn healthy -- burns more fossil fuel than the ethanol replaces [source: Pimentel]. Adding to this negative-sum equation, the irrigation demands to grow corn in drier locations have the potential to pinch water supplies, especially as farmers turn to ethanol production as a source of income [source: McKenna].

And then there's the economic factor. Between food production, animal feed and its other industrial uses, corn is in high demand. Adding ethanol producers to compete for the world's corn supplies means that prices for the crop -- and its subsequent products -- can spike with increased ethanol demand. Combine the factors and, though it's a useful biofuel, corn isn't likely to be the sole biofuel that tempers the world's dependence on fossil fuels.

This may be the most versatile biofuel on the list. Along with being a staple food product from Asia to America, the soybean has been turned into everything from ink and crayons to fuel products [source: Scharlemann]. While corn is the most popular base stock for the ethanol that is blended with gasoline to fight smog, soybeans are the main source for the oil used to produce biodiesel.

To produce biodiesel using soy, manufacturers first press the oil from the beans. Soy's high oil content -- about 20 percent of the bean is usable oil -- makes it an ideal candidate for this process. Once the oil is extracted and filtered, it's mixed with a catalyst that removes its glycerin. The remaining oil can be poured directly into a diesel engine's gas tank.

Biodiesel has a number of benefits over petroleum diesel beyond its being a renewable resource. It burns cleaner, meaning biodiesel-powered engines produce less of the particulate matter that can cause smog and health problems.

Palm trees are good for more than tropical scenery and coconuts. Their fruit's high-carbon shells can be turned into water purification filters, the leaves and woody parts of the trees have been used for structure and shelter for millennia, and the seeds' oil is now under consideration as a potentially mass-marketable biofuel.

But palm oil is possibly the most apparent example of a major problem standing in the way of widespread biofuel production. The space, energy and financial resources needed to produce the raw stock far outweigh the benefits of the end result.

Palm oil is a major crop in Southeast Asia. As demand increases for palm oil to produce biodiesel, plantations in countries like Malaysia and Indonesia are clearing vast swaths of rainforest to make room for more oil-producing palms. And the trucks, ships and production facilities used to move palm oil from these countries to the car- and truck-heavy West add to the fuel burned -- and emissions produced -- to bring this green fuel to market. Palm oil is not the only biofuel facing this dilemma, but its popularity and low cost mean it's encountered the problem on a wider, and more public, scale than many of the edible fuels that follow [source: Rosenthal].

If you've eaten French fries, onion rings or fish and chips lately, you may have contributed to another popular edible biofuel: used cooking oil.

Cooking oil that has been used to deep-fry food still contains the fatty acid alkyl esters that make it a viable fuel in some diesel engines. By straining the oil to remove food and breading flour, inventive biofuel makers can produce biodiesel, or simply run the oil straight into diesel engines using so-called "greasecar" technology.

With fast-food restaurants on seemingly every corner, and fried food a common part of many nations' diets, it would seem that frying oil could be the most readily available of all biofuels. But it does come with drawbacks.

First, used frying oil contains a lot of the food that was fried in it. Straining this out -- especially in cases where a lot of flour was used -- is a time- and labor-intensive process. Filtering large amounts of the oil can take too long for mass production. Furthermore, the end result may be a mixed bag; fry oil may come from peanuts, corn or other plant blends, meaning it's hard to tell how potent the fuel will be from batch to batch.

But many greasecar and biodiesel advocates are willing to put up with these problems. And since fry oil doesn't require expensive pressing equipment to pull its useful parts out of seeds or grain, it's a fuel of choice for inventors, experimenters and garage scientists who want to break free from petroleum on a budget.

Ah, the ever-versatile peanut. Though considered a legume rather than an actual nut, the peanut is arguably one of the most popular foods of its type in the Western diet. Between a sea of mixed nuts, peanut-y candy and the peanut butter sandwiches that fill millions of lunch boxes each school day, we are deeply attached to the lowly peanut.

The peanut has a number of uses beyond food, many of which were promoted by renowned African-American botanist Dr. George Washington Carver. His archives include lists of more than 300 uses for peanuts, ranging from dye and plastics to the oil that can potentially be used as a biofuel [source: Fishbein].

But peanuts are victims of their own popularity when it comes to biofuel. Because peanut oil can be used for a number of food, medicinal and industrial purposes, it's simply too valuable to convert into biofuel cheaply. In a case of simple economics, demand keeps the price too high to make peanut oil a practical, edible biofuel for now.

Cotton doesn't come to many people's minds as a food product. The main use of cotton in the modern world, after all, is as a fiber for cloth. But the oil from cotton seeds is a light, neutral-flavored vegetable oil that has been used for cooking in America since the 1860s [source: NCPA]. Cottonseed has also been used as animal feed, although using too much of it can lead to nutritional problems with livestock [source: Osborne].

Cottonseed oil's use as a biofuel makes sense: According to some analysts, there's more oil available per acre from cotton than from corn or soy, two of the most popular biofuel sources [source: Journey]. But cottonseed oil does have one drawback that, as with many other biofuels, presents a nagging engineering challenge.

Cottonseed oil begins to solidify in cold temperatures. A vehicle run on pure cottonseed oil would be unusable in winter unless it contained some type of oil-heating system that kept the biofuel above its gel point. More popular biofuels, such as soy biodiesel, encounter this problem, too. But while soy biodiesel gels at about -16 degrees Celsius, cottonseed oil gels at only -1 degree Celsius. Much of the world encounters colder temperatures on a regular basis, making pure cottonseed oil less than optimal for widespread use as a biofuel.

Safflower is a plant with a long history of use, perhaps beginning when the yellow flowers and oil-containing seeds were used to dye the cloth wrapping used in ancient mummification processes. More modern applications of safflower include widespread use as a natural medicine in both Eastern and Western cultures. Likewise, the oil from safflower seeds is used as a more heart-healthy substitute for other cooking oils.

Safflower oil has a low gel point, making it an interesting oil to consider for biodiesel production. But widespread use of safflower as a fuel source may be limited by its popularity -- or lack thereof -- in the agricultural world. The 604,000 metric tons of safflower produced worldwide in 2004 are tiny compared to corn or soy production, and it's a sharp decrease from the 800,000 to 900,000 tons typically produced per year in the mid-90s. Adapting safflower harvests to meet biofuel demands would mean reversing this trend and producing significantly more of this ancient, multipurpose plant [source: Jimmerson].

Linseed, or flaxseed, oil is a good example of the versatility of many vegetable oils with biofuel potential. Woodworkers mix this oil with a thinning agent, such as turpentine, and use it indoors to condition furniture, fixtures and hardwood floors. The oil penetrates the wood, preventing it from becoming too dry and cracking or scuffing. Outdoors, a similar treatment prevents wood from absorbing too much water, which would hasten weathering and rot [source: DIY].

Linseed oil without the thinning agent has been shown to be a valuable preservative for human health, too. Like a number of other vegetable oils mentioned in this article, linseed oil appears to lower cholesterol and promote heart health [source: Ridges].

The plant fibers in flax are used to make linen, meaning that this biofuel crop can be used for both its seeds' oil and its stalks' fiber. This multiuse nature could make linseed oil a more attractive biofuel than other crops whose nonseed parts lack the value of flax [source: Shirke].

Sorghum is one of the world's most important cereal crops and a major agricultural export for the United States [source: Council]. It's used in foods ranging from beverages to cakes and cookies, and the high-antioxidant, gluten-free nature of some varieties make it a valued grain for health-conscious bakers.

Sorghum also has the potential to be a knockout of a biofuel. Different strains of the grain can grow in a variety of climates, and its biochemical makeup means it can be interchanged with corn in ethanol production processes. Researchers are developing hybrid strains of sorghum specifically for biofuel production, so it's possible that, before long, the E85 you put into your gasoline-powered car's tank may have something in common with the molasses cookie you buy in the convenience store [source: Lau].

OK, water isn't technically a biofuel. It's a vital natural resource without which life wouldn't exist. But thanks to a deceptively simple technology, water could one day be a conceivable source of fuel.

The simple process of electrolysis, in which electric current is passed through water, breaks the liquid into its base elements: hydrogen and oxygen [source: Nave]. Hydrogen is an excellent fuel -- it carries three times the energy per pound of gasoline and combusts without the harmful emissions of petroleum fuels [source: Stanford].

But hydrogen production and storage are problematic. Moving large amounts of super-light, highly combustible gas around the world could pose major safety issues, and the amount of hydrogen needed to power a car for a long trip would require an impractically heavy fuel tank to keep enough fuel onboard in a safe manner [source: Planet].

Hydrogen's far from a lost cause, though. One technology, made famous by the mysterious Garrett Water Carburetor, involves mounting a hydrogen-producing cell on the vehicle and running it with electricity from the engine's generator. Modern versions of this idea inject hydrogen into gasoline-powered engines, generating cleaner emissions and better mileage. The technology has some cost, reliability and development hurdles to overcome, but it's possible that part of your car's near-future fuel will come from your home's spigot [source: Brooks].