Heat Gun / Soup Can Nano-Roaster

I'd been roasting with a heat gun and dog bowl for several months when I happened upon Tim Eggars soup can roaster. I first bumped into this on homeroasters.org. I liked the simplicity of a heat gun, a steel bowl, and a wooden spoon, but roasting sequential batches was tiring, so I had to try the soup can. (If you're ever hunting for ideas, or for proof that this hobby can turn into an obsession, Sweet Marias has a gallery of do-it-yourself roasters.)

Tim uses a gas burner underneath the can, but I, as others have done, aim the heat gun into the can. This creates an asymmetrical heat source. To adjust for this, I tilt the can. And I angle the agitating fins to move the beans toward the center of the can. The diagram at right tries to shows the placement of the fins.

I originally used pop rivets to secure the fins, but Eggars' method of cutting slots with a Dremel is quicker and easier, and beans are less likely to get stuck. With a pop rivet, the entire fin is inside the can, and beans can become caught where the fin bends.

This setup is good for test batches, roasting 2 to 2.5 oz at a time — or around 8 brewed cups of coffee.

At left is the can itself. I had planned to wrap the can with a strip of fiberglass insulation to reduce heat loss when roasting outdoors. But the rag I used as a stop-gap measure works well enough. I'm roasting indoors, now, and the rag allows me to keep the heat gun on a lower setting. And it helps prevent burns — though the hose clamp still gets plenty toasty.

After several months of use, small cracks began to radiate from the hole around the bolt, due to the constant thermal pounding. So I replaced the original bolt, seen here, with a sturdier one, and placed washers on either side of the can to shore it up. These show up in the subsequent pictures.

The soup can is actually a stew can — the same diameter as a wide-mouth canning jar ring.

The foil that partly blocks the can's opening I cut from a Stouffers macaroni and cheese container. 3 or 4 tabs protrude from the outer edge of the foil and are under the canning ring to keep the foil in place. The wider section of foil blocks the beans as they tumble over the front fin.

You can see the fins in these shots.

In the interior view at right, the front fin is on the left. If you compare the angle of the fin to the concentric rings on the sides of the can, you can see that the fin is not perpendicular, but runs at a slant.

The can rotates counter-clockwise, so when the beans tumble over the front fin, they should also slide down toward the middle of the can.

Tim Eggars' design has the advantage of a good, uniform heat source along the bottom of the can, but I'm fond of the heat gun because I don't have to deal with combustion gases, and I suspect it uses a little less energy overall. By angling the fins, the beans roast fairly evenly, and the heat gun roast retains more of the aromatic flavors typical of an air roast.

Here's the setup. (If you happen to have a heat gun and cordless drill already, materials cost about $5.00.)

You can barely make out the smaller hose clamp at the bottom of the drill's handle, just above its battery. Once you've adjusted the clamp to produce 40 rpm or so, you can slip it on and off the trigger without further adjustments. You want to keep the beans moving, but not so fast that they bunch down toward the bottom of the can.

The heat gun is positioned so that it doesn't blow directly on the beans. Due to the angle of the can, the blast of hot air primarily hits the back of the can above the beans, although they are lofted briefly into the heat by the fins. My thought was to try to split the difference between an air and a convection roast.

The drill is propped up to help prevent beans from spilling. The drill and its prop are sitting on a thin piece of plywood. This makes it easy to slide the can nearer and farther from the heat gun as needed.

My $20 heat gun has a low and high setting. I've been experimenting with roasting beans entirely on the low setting. This was too slow for outdoor roasting, but works indoors.

I generally roast with this "profile": 3 minute drying of beans with the can 1" from nozzle. Then 0" from nozzle until beans reach active 1st crack. Then 1.5" - 2" away until 1st crack subsides. (Depending upon the beans acidity, I may extend this lull in heat for a bit.) Finally, I return the can to 0" away until the end of the roast.

With 2oz of beans, 1st crack usually starts between 7:00 - 8:30, with 2nd following between 9:00 - 11:00 — depending upon the variety of bean.

Below the can is the cooling tray — just a cardboard box with the bottom cut out and a piece of hardware cloth duct taped inside. Eventually I'll build a light-weight hemlock box.

The entire contraption sits below an ancient ceiling fan in our out-of-code basement bathroom. When the roast is finished, I dump the beans into the box, then hold it under the fan.

The beans cool in about 1 minute. At right is 2 oz of Guatamala Oriente cooled just as it entered 2nd crack.

Here's a short, uneventful movie of the roaster in action. The beans are about 5 minutes into the roast, a couple of minutes prior to 1st crack. The beans have been dried out, and the can is now close to the gun to ramp up to 1st crack. (The gun is a little lower than normal, here, and the rotation a bit faster, but the batch came out fine.) In this otherwise unremarkable video, you can see the chaff is separating from the beans and blowing out of the can.

(If the video window turns white, you may need to scroll the browser window.)

Other roasting methods I've tried

  • Hearthware I-Roast I.

    My first roaster. I burnt it out after 8 months from overuse. I found it really hard to control, but was hooked on roasting nonetheless.

  • Stovetop Popper.

    Since we lack a good kitchen fan, and since my family inexplicably doesn't like the smell of coffee, roasted or otherwise, I found consistent results challenging outdoors. Occasionally good batches, particularly for darker roasts. Much better for peaberries than flat beans.

  • Heat Gun / Dog Bowl (actually, stainless steel pot)

    During good weather, often excellent results — especially for a press pot. Tougher to get good results on cold, windy days.

    5-6oz per batch generally yielded more uniform results than smaller batches. 3 or 4 batches in a row were an efficient route to tennis elbow.

    Like an open pan on a burner, this method is a quick way to develop good instincts about roasting — the sound, smell, and look of the beans are all readily apparent.

  • Heat Gun / Soup Can

    (This was my neighbors' favorite method. My setup was next to their kitchen porch, and they, as right-thinking people do, love the smell of coffee.) Outdoors in good weather, yielded good, sometimes excellent results. Consistency still a struggle, particularly in colder weather.

    Indoors, I've been very happy with the results. Roasts are much more predictable and reproducable. Small batch size is a disadvantage, unless you love frequent roasting. And, it's effortless. It's also nice not to be turning wooden spoons into charcoal, as happens with the dog bowl method.

  • Behmor 1600

    Here's my trusty Behmor in mid-roast.

    I use this when roasting for espresso. The P2 profile is a little tricky but good for knocking down acidity. The Brazil Ipanema Tree Dry Process, the Ophiolite Blend, or the Puro Scuro roast beautifully in this machine.

    However, I much prefer the heat gun for press pot coffees. High-grown Ethiopia, Yemen, or other aromatic fruity or floral coffees taste a bit dull to me, muted almost beyond recognition when roasted in the Behmor.

    On the other hand, I have better luck in the Behmor with coffees from Brazil, which I find trickier to roast with a heat gun.

    NOTE: the Behmor depends on adequate voltage. As everyone says, a Kill-o-Watt is an indespensible accessory.

    Many users also mention the timer. They'd prefer a count-up to a count-down timer. I've modded my Behmor to have both — nothing like a cheap count-up timer with a magnet.

Below is a short movie of a good double shot from 15 grams of Brazil Ipanema Tree Dry Process beans. (They're from a 4oz batch roasted in the Behmor. The Behmor was set for a 1/2lb on the P2 C profile, and the roast was cooled 6 snips into 2nd crack).

Producing something like this.

The crema on this 1.5oz double shot is thick and uniformly-colored. A 0.75oz ristretto will be darker and less uniform. (The pours on the latte art page were into ristretti or into divided double shots.