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.