Biofuel is a hot subject. We are hearing a lot of talk and debate about an alternative to gasoline called a renewable biofuel. Made from corn, it could reduce greenhouse gasses, roll back higher costs, and minimize our dependency on Middle East oil.

All of the biofuels have their origin in the sun. Both coal and crude oil and all the products made from them are biofuels and by-products from sunlight made in a process of photosynthesis in plants and then consumed by animals living millions of years ago. The organic chemical remains of those plants and animals were stored in the earth where they changed chemically as influenced by changes in the earth's crust.

The current attention to biofuels is directed toward renewable fuel from plants growing today. Renewable biofuel is essentially ethyl alcohol (usually called ethanol) recovered from plants in a process of fermentation and distillation. It's the same process used to make vodka and other distilled spirits.

By law, Chicago area cars are already burning a mixture of 90% gasoline and 10% ethanol. General Motors has over 2 million FlexFuel Vehicles on the road designed to operate on gasoline E85 (85% ethanol and 15% gasoline) in addition to regular gasoline.

Illinois agricultural products, including corn and soy beans, are excellent sources of ethyl alcohol because of their high sugar and starch content.

This plant is typical of farmers' cooperatives producing ethanol from corn.

That's why corn and beans produce more ethanol by weight than grass or weeds. Sugar cane is another excellent source of ethanol derived from distillation. If you don't mind the need to handle more material, you can also make alcohol from grass and just about anything that grows in sunlight even after it has been digested and excreted by farm animals.

Another advantage is that alcohol burns without polluting the atmosphere. Water and CO2 gas are nearly all that's left over when alcohol burns. Since the carbon in ethanol was recently extracted from atmospheric carbon dioxide by growing plants, burning it does not result in a net increase of carbon dioxide in the Earth's atmosphere. As a result, using ethanol and other biofuels such as vegetable oil to replace diesel fuel are seen as a way to reduce the amount of carbon dioxide released into the atmosphere.

The main benefits are important. The whole biofuel process is biodegradable. And, most experts agree that a gallon of ethanol produced locally will be much less expensive than a gallon of gasoline.

This is all very good news, but there is more to the story. Ethyl alcohol does not produce as much heat energy as gasoline by volume when it burns.

• l Ethanol energy content: 75,700 Btu/gallon
• l Gasoline energy content: 125,000 Btu/gallon

In simple terms, this means you can't go as far on a gallon of ethanol as you do on a gallon of gasoline. While mileage can be improved by mixing in various amounts of gasoline, the net result is lower mileage ethanol and ethanol blends. Depending on the price, the cost of traveling a mile may be no different and even more than gasoline.