In its early days, biodiesel was the sole domain of quirky environmentalists schlepping their vintage Mercedes-Benz sedans and Volkswagen vans from one fast-food restaurant to another to fill up on deep-fryer slop. You could often tell where these forward thinkers filled up their cars by what the car's exhaust smelled like. "If you went to a Chinese restaurant, you smelled wontons while you were driving," says former Mercedes biodiesel owner Lenny Hoffman of Santa Fe, N.M. "After a doughnut shop, you smelled fried dough." The adage "you are what you eat" can still be applied to biodiesel engines: Fast-food grease sends a french-fry essence out your tailpipe, coco-diesel leaves a sweet smell in your wake.

And while many Americans still go restaurant hopping, trailing clouds of onion-ring odor or re-living Thanksgiving in a plume of turkey grease exhaust, biodiesel production is becoming increasingly sophisticated. It has moved beyond just recycled vegetable- and animal-fat-based cooking oils to fuel made from primary and surplus farm crops. As the appetite for alternative fuels grows, some farmers are even harvesting crops like mustard and safflower to convert the seeds into fuel to power their own machinery, reducing their dependence on conventional energy sources.

Discuss:
Can biodiesel save the world?

What is Biodiesel?

Technically speaking, biodiesel is what's produced by combining vegetable oil or animal fat with alcohol (typically methanol or ethanol). But biodiesel is often a catchall phrase for nonpetroleum-based liquid fuels used in engines designed to burn petroleum-based diesel. This includes biodiesel or straight vegetable oil or grease (of the kind you'd pick up at a McDonald's).

According to biodiesel.org, biodiesel is better for the environment because it is made from renewable resources and it has lower carbon emissions than petroleum diesel. It's also less toxic than table salt and biodegrades as fast as sugar. Since it can be made in the United States from organic matter, biodiesel helps decrease our dependence on foreign oil and benefits local economies where it is produced.

Biodiesel can be used in pure form (B100), but it's usually blended with petroleum diesel. B20 (a blend of 20 percent biodiesel with 80 percent petroleum diesel), for instance, has significant environmental benefits and is sold at some of the 650 biodiesel stations currently open nationwide. Some older-model diesel vehicles must undergo a biodiesel "conversion" process, which involves switching out rubber gaskets and hoses for ones that are nonreactive to biodiesel and changing the fuel filter to protect fuel lines from the breakdown of residue deposits.

What's in a Smell?

Much the same way certain varietals of grapes are identified with certain regions around the world, different crops are becoming associated with biodiesel production in different states. In central Texas, cottonseed oil is the brew of choice; in parts of Wisconsin, it is sunflower oil; and in Indiana, soy biodiesel is popular. In Missouri, a company called Changing World Technologies is making a name for itself by converting Butterball turkey parts into fuel.