First comes the discovery that it's possible to roast coffee at home, and sites like Sweet Maria's. Finding a local distributor of the Hearthware Precision coffee roaster saw me happily roasting up to 80 grams of coffee.

But, as always, UpgradeLust™ kicked in at the thought of BBQ Grill roasting. About the time I gave up making my own drum as a bad joke, Ron Kyle started offering prefabricated drums for sale. Dispite the shipping costing almost as much as the drum, I had to have one. And I now do, #15.

Comments on Sweet Maria's mailing list about standard 6rpm rotisserie motors not being fast enough saw me manually cranking the drum for the first few roasts. Good exercise, but it gets tedious very quickly.

If you're reading this and live in the US, take yourself off to the Surplus Center where you'll find no end of motors, suitable for cranking a drum at 30-60rpm.

If you're still here, you're either The Rest Of The World, or cheap. Since I fall into both categories, I thought I'd follow this guy's lead and try using a windscreen wiper motor.

And here's the result:

It'll turn a drum loaded with 1.2kg of coffee at 44rpm.

How to:

You'll need

  • a grill. Go overboard on the BTUs
  • a roasting drum.
  • a multi-segment BBQ rotisserie rod, one that screws together. Something like this kit. Must have a screw on the end of the rod
  • a windscreen wiper motor. Dirt cheap from a car wrecking yard.
  • Nuts. The metal kind.
  • 2 Socket drivers of the correct sizes. One sized to fit over the nut on the wiper motor; the other a "deep" socket sized to fit over the nut that you put on the end of the rotisserie rod.
  • a 1/2 inch universal joint
  • a length of 1/2 inch steel tubing
  • a 12 volt car battery or some other power source such as a mains adaptor
  • angle brackets
  • a metal plate
  • bolts & nuts
  • wiring
  • a modicum of mechanical & electrical aptitude.

    Slide one socket driver onto one end of the 1/2 inch rod. On the other end put the universal joint. The other socket connects to the universal joint.
     
    The windscreen wiper motor is bolted to a metal plate, which is bolted to angle brackets, which is bolted to the grill, which is connected to the knee-bone. Uh, sorry. Wrong jingle.

    Here's a shot of the universal joint in action. Removing the drum is simply a matter of lifting it up and pulling sideways so the socket driver disengages.

    The electrical side is only slightly tricky. The motor will have around 6 leads hanging free.
    (Safety note: during testing and operation keep your hands away from the rotor, since it's got enough torque to mangle any fingers that get caught.)
    Take your power source and briefly connect them to any two leads. If the rotor doesn't move, try another two. What you'll find is that two wires will have the rotor turning slowly, another two quickly. To have the rotor turn in the opposite direction simply swap the leads from the power source.

    When you know which wires are which, extend them by soldering a lead onto them. A couple of meters should be ample. If you're connecting to a battery, put a switch in line. If using a mains adaptor you can use a mains switch.

    btw: you need a switch of some kind. Having connectors that need to be unplugged is not a good idea, since you need to work fast when the roast is done.

    To fine-tune the speed of rotation you can get mains adaptors with variable DC output. The motor will turn slower at lower voltages, and faster at voltages.

    Dealing with 1 kilo (and up) of coffee at over 400 degrees F needs the right cooling gear. I found a jumbo-sized collander at a restaurant supply store. That sits on a $10 stainless steel rack I got at Ikea. The rack rack in turn sits on an industrial exhaust fan. Add a wooden spoon and I can get the beans down to warm in a couple of minutes.

    Now all I need to do is add a motor to that so I don't have to stir the beans while they cool.. ;)

    Paul Haddon
    Sydney, Aus

    paul{at}haddon.org

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