I’m : a programmer, writer, podcaster, geek, and coffee enthusiast.

“Coffee-powered car”

A few people have sent me this story about a “coffee-powered car”, which is a great headline but isn’t actually true:

Instead of the brewed beverage, the vehicle is fueled by pellets made from the chaff that comes off of coffee beans during the roasting process, which is then heated and broken down into carbon monoxide and hydrogen, the latter of which is cooled, filtered and combusted in an internal combustion engine.

The process is called gasification and works with just about any carbon-based substance.

Indeed, the car is basically powered by burning wood pellets, and packed coffee chaff can be substituted for wood. So how much chaff does it need?

The creator of the vehicle, Martin Bacon, tells that the vehicle can travel about 55 miles on a 22-pound bag of pellets, which in wood form costs about $2.50.

This would be interesting, but chaff is nearly weightless. It looks like a lot of volume, but even the slightest air current blows it away. How much coffee do you need to roast to get 22 pounds of chaff?

Here’s most of the chaff from my roast this morning. Some burns off during roasting, and a few flakes come out with the beans, but this is the majority of it, taken from the roaster’s chaff tray:

It’s not enough to register my scale’s minimum measurement of 1 gram of chaff for this half-pound roast.

I don’t know how much chaff a big shop roaster leaves behind after a big roast. (I can’t find this information anywhere, but I’d love to hear from a pro roaster who knows.) Maybe they can get more.

If we generously assume that they can yield 2 grams of chaff per roasted pound, and that chaff pellets produce the same amount of power by weight as wood pellets, they’d need to roast about 5,000 pounds of coffee to produce the 22 pounds of chaff needed to power this car for 55 miles. And that’s not including the energy required to collect all of this chaff and pack it into pellets.

It’s pretty far removed from what most people would assume you mean by a “coffee-powered car”.