The Why Files The Why Files --

Brewing a new fuel source
White bucket spills black coffee grounds onto table, next to a cup of coffee
The remains of the day, coffee-shop edition

Fess up. Faced with the morning craving for caffeine, do you, with trembling hand, pour that first delicious, nutritious cuppa joe, and then just trasho the soggy coffee grounds?

Maybe you're a caffeinated eco-freak, and you diligently compost the stinky remains. That's better.

But instead of deep-sixing the dregs of your addiction, why not transform them into diesel fuel? In a new study, Mano Misra of the University of Nevada calculates that the 16-billion-pound global coffee crop could still supply the essential nectar of bean -- and about 340 million gallons of diesel fuel.

That's less than 1 percent of the diesel used on American roads, but recycling this waste eliminates a disposal problem and reduces greenhouse gases emissions, so let's hear Misra out.

Or maybe not, since Misra did not answer his phone -- out scrounging one last cup of mud, perhaps?

Photo:Imperium Renewables biodiesel plant in Grays Harbor, Washington, skidrd
This biodiesel plant can make 100 million gallons per year, assuming it can find affordable feedstocks. Will this plant start "drinking coffee"?

Grounds for hope?

Misra's study points out that since biodiesel (fuel produced from vegetable matter instead of petroleum) first gained notoriety a decade ago, production has been hobbled by a shortage of raw materials. Biodiesel is expensive to make from crops like rapeseed or soybean. Waste products like fat and restaurant grease can also be converted to diesel, but even in fast-food-frenzied America, the supply of spent grease is limited.

A clear glass jar with a black cap, half filled with 75 milliliters of amber-colored biodiesel
This vial of biodiesel originated in spent grounds from a Reno, Nevada, Starbucks.
Photo: Narasimharao Kondamudi, University of Nevada-Reno.

To produce JavaFuel, Misra and colleagues cadged and dried some spent grounds from Starbucks, extracted the oil with solvent, and put the oil through the chemical process of transesterification. The resulting biodiesel weighed 11 to 20 percent of what the dried grounds had weighed.

The aromatic fuel

Tantalizingly, the scent of CoffeeDiesel is reminiscent of the black brew that supplies our morning buzz. That's a big advantage over BioGrease, which can carry the aromatic memory of fried fish. The boatload of antioxidants in coffee also make the fuel more stable than conventional biodiesel.

The scientists estimate that their process could turn a profit of more than $8 million a year in the United States, and plan to develop a pilot plant to produce and test CofFuel.

Questions remain: Would the "ground round" needed to collect grounds from coffee shops save energy or waste it? Would biodiesel have more "jump" if sourced from espresso rather than truck-stop joe? And if the caffeine content is high enough, will people quit guzzling BioCoffee and switch to BioTrucker?

- David J. Tenenbaum

coffee bean


What's your favorite use -- fanciful or practical -- for spent coffee grounds?

Send us your ideas and we'll post the best here. Please keep it short -- 25 words max, and include your location....

The ground rules:

You send us ideas, we print them if we choose. You don't copyright, patent, or otherwise protect your ideas. We don't guarantee anything about this process. If you try these ideas, use common sense and don't sue us!

Winners so far!

  • compost for growing flowers. Coffee is very rich in nitrogen. --Guillermo N., CA
  • Handy for traction on a slippery driveway. Location: The top of a slippery driveway in Wisconsin. --Terry D., Cross Plains, WI
  • Organic landscape paint so we can pretend it's spring. --Madison, Wisconsin (where life is glacier-gray right now!)

coffee bean

Related Why Files

The origins of oil.

• Don't talk trash about reused refuse!

• World hunger for biofuels impacts the world's hungry.

• Environmentally friendly ethanol: kernel of truth or just corny?


• Waste coffee grounds offer new source of biodiesel fuel, Mano Misra et al, _Journal of Agricultural and Food Chemistry, Dec. 2008.

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