My 15-Year Quest to Make the Ultimate DIY Coffee Roaster

Food & Beverage Maker News
My 15-Year Quest to Make the Ultimate DIY Coffee Roaster

Bean Back Better: How I built — and rebuilt, and rebuilt — 22 versions of the perfect homemade coffee roaster

I’m a coffee addict — just not the usual type. I can’t even settle for buying a pound of Peet’s whole beans, grind and brew them, then relax with my cup of hot coffee and Reddit. My coffee must come from beans that I roast. 

In a coffee roaster that I built.

Way back in 2006, while visiting my son Mike in Portland, Oregon, he offered me a cup of coffee. Seems like a perfectly normal thing to do, right?  Not really, because up to then I had never drunk a full cup of coffee, and he knew it. Even survived four years of quasi-derision in the Navy from the old salts: “Mr. Cotton, you’ll never survive the US Navy without coffee.” (They were wrong.)

When Mike offered me the brew, I balked: “You know I don’t drink coff—” 

He interrupted, “Just try this, Dad.”  So I did, and guess what?  It was delicious and refreshing — exactly what I needed at that particular 3-time-zone jet lag moment.

After returning to the East Coast I began searching for another great cup of coffee. I tried a few old standbys and a few boutique brands. Some were awful, some were OK, a couple were even quite good. But then I stumbled on the home coffee-roasting phenomenon. (Googling that subject today yields over a hundred million hits.) Confirmation: the fresher the better! Next time you pick up a bag of coffee at the supermarket, look for the date it was roasted. Shameful.

Some of the advantages of home roasting are:

1. It’s actually quite easy.

2. It’s inexpensive. The average cost of a pound of decent green (unroasted, raw) beans is about the same as a pound of medium-ground Folgers. (Since green coffee beans lose moisture during roasting, it takes a bit more than a pound to yield 1 lb. of roasted coffee.)

3. Green beans are readily available from many online suppliers, such as Sweet Maria’s.

4. They have a long shelf life (a couple of years, at least), so you can buy larger quantities, saving per-pound and shipping costs.

5. You can create your own custom blends.

6. You can batch-roast as much or as little as you like, as often as you’d like.

7. You can control the roasting times and temperatures (known as a profile) to yield light or dark roasts, or anything in between.

8. It’s fun!

Commercial home coffee roasting machines, of which there are many, are somewhat expensive — especially those that can handle a significant amount of coffee. One option tempted me: repurposing a hot-air popcorn popper, as other folks have done and still do. But its capacity is minuscule, and I like to make stuff, so I decided to build my own roaster.

Four things are important to me (coffee-roaster-related!): It’s gotta be cheap, it’s gotta be relatively easy to make, it shouldn’t take up much space, and it must — must — work very well. To these ends, I chose readily available, inexpensive, robust materials and components for my roaster builds. 

So here are ten of my finished machines, presented in chronological order, from a total of 22 that I’ve made.  The first four builds include links to online articles in Make: magazine.

Keep in mind that all successful coffee roasting machines (from the tiny to the behemoth) must do two things very well: keep the beans moving, and furnish an even amount of relatively high heat for around 10-15 minutes. (Big commercial machines can take a bit longer.)

Figure 1. Our saga begins in 2006 with the propane-powered Nirvana Machine.

I. The Nirvana Machine (Make: Volume 08)

After much sophisticated (ha!) research and many mostly unsuccessful attempts — not to mention burned beans — a decent small-batch roaster finally evolved, which I optimistically dubbed The Nirvana Machine (Figure 1). Easy to build and use, it roasts about a half-cup of green beans, which yields about 3/4 cup after roasting. Green beans (very hard, grey-green seeds that smell a bit like, um, grass) were at that time more easily bought from commercial coffee roasters. 

The Nirvana Machine had two big advantages: it was easy to see the beans while they’re roasting and it was portable, powered by batteries and a small propane camp stove. (One of the biggest annoyances of most coffee roasters is that it’s difficult to see (and hear) the beans as they’re roasting.) Completely different from anything on the market, it roasted the beans in an open-ended spinning wire-mesh bean basket tilted at a 45-degree angle over a camp stove. Commercial, and some home-roasting, machines include a built-in “tryer” to monitor the roasting progress. The tumbling basket exposed all the beans to the same heat. The basket could have been spun by hand, but I’m not a fan of cranking. So I used a $10 battery-operated, Black+Decker (hereafter referred to as B+D) AS6NG screwdriver (amazingly still on the market), reconfigured to use 2 D-cell batteries. Yes, it needed to run at half-speed, but it readily turned the bean basket.

Heat from the propane burner was monitored to roast the beans evenly and not burn them; a few ounces of beans usually needed around 10-15 minutes for a medium roast, depending on ambient temperatures. The little roaster even served for the occasional camping trip (if I didn’t forget batteries!), along with a manual coffee grinder. I’m not aware of any self-powered roaster commercially available today.

The build plans are still right here:

Figure 2. An ambitious, semi-automated version of the original propane roaster.

II. Semi-Automatic Coffee Roaster (Make: Volume 46)

Soon I began to think of ways the experience could be even more satisfying.  Aha — the roaster should be automated, set-and-forget, and continuous. Rather than build a whole new one, I started with the Nirvana Machine. Eventually, after much contemplation and consternation, a new roaster emerged that loaded, roasted, and dumped the beans under microprocessor control.

The finished, clearly over-elaborate machine (Figure 2) was impractical and definitely not portable, but tons of fun to design, build, and use. I wound up using three B+D screwdrivers controlled by an ancient Parallax HomeWork microcontroller board. One rotated the bean basket. Another, using a worm gear and a bandsaw-cut 60-tooth gear, moved the constantly spinning basket through a 135-degree arc into three positions: vertical to load the beans, at a 45-degree angle over the propane stove for roasting, and horizontal for dumping the beans into a fan-cooled wire mesh tray. The third screwdriver rotated a plastic bean-loading auger — a mechanical and pecuniary challenge, as it’s typically used vertically in a chocolate fountain!

There’s a one-page summary in Make: Volume 46, and here’s a link to the build saga:

Figure 3. My automated version of the popular dog bowl coffee roaster, using a heat gun instead of propane stove.

III. Dog Bowl/Heat Gun Roaster (Make: Volume 65)

One of the more web-popular, cheap, non-commercial, quick-and-dirty ways to roast a decent amount of coffee at home is with a heat gun, a stirrer such as a wooden spoon, and a (new) dog bowl. Yep, a dog bowl.  Pour in a cup of green beans, point a heat gun (normally used for removing paint and such) at them, stir like mad while simultaneously waving the heat gun at the beans, and about 15 minutes later enjoy an OK batch of home-roasted coffee. I’m defining “OK” as mostly evenly roasted, with a few light beans and a few almost burnt ones.

But I found no heat-gun/dog bowl roaster on the web that was even slightly automated, so natch I cobbled up a machine (Figure 3) that held the bowl, the heat gun, and two B+D screwdrivers. One turned the bowl, thanks to the bowl’s rubber anti-skid ring; the other one stirred the beans with a hand-made spiral whisk. I chose the cheapest heat gun on the market — Harbor Freight 56434, for about $17 — and screwed it firmly in place, pointing at an angle to the beans in the bowl. No waving around necessary. To ease bowl and bean removal, I added a kitchen mixer-like pivot to rock the stirring motor out of the way. Automation produced a much more evenly roasted batch of beans.

Here are the plans:

Does it seem like I’m slightly hooked on this off-beat hobby?  Sure: fresh-roasted coffee literally courses through my veins. And I was still hell-bent on building an even better roaster, always with my new mantra in mind: CREW — Cheap, Reliable, Easy to build, and Works great!

Figure 4. Upgrading from dog bowl to flour sifter.

IV. Simple Sifter Coffee Roaster (Make: Volume 71)

At this point I was enamored with the cheap Harbor Freight heat gun. There’s no better value, really, and it gets plenty hot on normal house voltage, cranking out 1500W on its higher setting. The home-built roasters on the ‘net use it a lot, either with a dog bowl or occasionally a modified bread machine or a flour sifter. 

Wait, what — a flour sifter? Sure! Mount it an inch or so over a heat gun pointing straight up, add some green beans, and turn the crank for a few minutes. Ta-da — home-roasted coffee!

Of course removing the sifter crank handle was a must — no manual cranking for me! This time I used a 12VDC motor from Amazon, powered by an adapter. The motor’s smaller than the B+D screwdriver and relatively easy to couple to the cut-off end of a sifter crank. It turns at approximately 60rpm and the sifter usually worked well. However, an errant bean would occasionally jam between the wires and the inside wall of the sifter, stalling the motor. Since I monitored the roast constantly, I could quickly reverse the motor with a DPDT switch between the adapter and the motor, which usually freed the jammed beans.

But “usually” wasn’t good enough, so I replaced the beater wires with two twisted paddles, 180 degrees apart.  No more bean-jammin’. The sifter then easily agitated 1-1/2 cups (9-10oz) of green beans, which yielded almost 2 cups roasted.

For easy bean dumping, the front edge of the sifter (opposite its handle) hinged on a vertical wood support.  This allowed users to simply lift and pivot the sifter to dump the roasted beans into a waiting cooling tray.  An SPST switch under the handle turned the motor off while the beans were dumped.

Speaking of cooling: coffee beans crave to be cooled immediately after they’re roasted. (They’re in the neighborhood of 400°F–450°F.) Skip this step and your lovely beans will “cook” significantly more and will emit considerable grayish-blue smoke (if they haven’t already). My goal has always been to stop the roast just into the second crack, when the smoke usually starts in earnest. 

OK, about cracks: Coffee beans make crackling sounds at two points during a roast, cleverly called first and second crack — often referred to as 1C and 2C — caused by the expansion of the beans as they’re heated.  When the beans expand, they shed light, thin chaff, or silverskin — the outer covering of the green beans.  Further into the roast they crackle more quietly, which to me means “get ready for a quick-cooling dump” into either a large baking pan, which makes a great heat sink, or a fan-cooled wire-mesh tray. Another popular small-batch cooling method is to quickly dump the beans into a metal colander. Then shake, shake, shake.

The roaster is shown in Figure 4, and can be updated to a Wobble Disk roaster by replacing the paddles, detailed in Volume 76 of Make: magazine.

Complete plans are here, including an optional dual-fan cooling tray:

Figure 5. Total overkill: automated feed auger, bean stirring, and dumping of the finished beans.

V. The Bean Machine (early 2020)

This microprocessor-controlled version of the Sifter Roaster (Figure 5) was also overkill; don’t attempt to build it! One B+D screwdriver loaded the beans using the the same chocolate fountain auger from the automated Nirvana Machine. I sawed the handle off the cheap Harbor Freight heat gun to save some space. Another screwdriver spun the bean-stirring paddles. When the beans were fully roasted, pressing a small switch started a third screwdriver that controlled the rack-and-pinion dump sequence. (The rack and pinion came from a cheap camera tripod and worked great!)

Here’s a video, compliments of Sweet Maria’s (a popular website for home coffee roasters):

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Figure 6a. Mounting an eccentric Wobble Disk in the sifter greatly improves the evenness of roasting.
Figure 6b. My first roaster built around the Wobble Disk.

VI. First Wobble Disk Roaster (late 2020)

This roaster is a mash-up of previous roasters, built around only the guts (heating element, fan, and fan motor) of the Harbor Freight heat gun. I removed its plastic housings, rescuing only the above guts, which were thankfully all electrically connected. I replaced the sifter wires with a 5-1/2″-diameter disk made from 1/32″-thick stainless steel sheet, mounted on the sifter shaft at a 45-degree angle. The Wobble Disk was born!  When turned by a small 12VDC motor, it tossed the beans back and forth in the sifter, ensuring very even roasting.  See Figures 6a and 6b.

Figure 7. Replacing the flour sifter with a smaller, DIY version.

VII. Second Wobble Disk Roaster (early 2021)

This roaster (Figure 7a) used the same principles as VI, but was even more compact. To make it smaller, I made the ‘sifter’ by rolling up two layers of 10″-wide aluminum flashing into a cylinder. I fashioned its sieve from ordinary window screen by forcefully pushing it down over a crude silo-shaped form (Figure 7b), then screwed it into the cylinder. I used the same motor and couplings to power another slightly smaller Wobble Disk which I cut from a small aluminum pizza pan: much easier to fabricate and much cheaper than stainless steel.

Figure 7b. Smooshing metal window screen around a rough wooden form to fabricate my own “sifter” sieve.

The lower housing (mostly aluminum flashing and three wooden legs) surrounded only the guts of the heat gun. Its legs also supported the upper housing. Overall height was reduced by 2″ and the diameter reduced by about 1″ compared to the first Wobble Disk roaster.

The other unique characteristic of this roaster was the use of two pairs of 1/8″-thick, 1/2″-diameter neodymium magnets. These were located under the wooden handle to hold the housings together while in use and also to conduct 12VDC to the motor. When the upper housing was lifted to dump the beans, the magnets separated and cut power to the Wobble Disk motor.

Sweet Maria’s put a video online here:

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Figure 8. A simple “pot” handle stays cooler and makes dumping easier.

VIII. Wobble Disk ‘Pot Roaster’ for Heat Gun or Gas Grill (early 2021)

The ‘Pot Roaster’ (Figure 8) features a Wobble Disk bean-stirring module with a horizontal wooden handle, giving it a pot-like appearance while keeping the handle further from heat. The handle is mounted to another aluminum-flashing cylinder surrounding an 8-cup sifter sieve. That fits onto a lower housing containing the heat-gun guts, similar to the other Wobble Disk roasters. It can also be used over a gas grill with a standard galvanized steel heat-duct adapter (Figure 9).

Figure 9. The pot roaster can also be adapted to a gas grill instead of its usual heat gun base.
Figure 10. All-in-one housing — just turn the whole thing over to dump finished beans.

IX. All-in-One Wobble Disk Coffee Roaster (mid-2021)

This one is similar to VI (above), is a bit harder to build, but is probably the most professional looking of the lot (Figure 10).  Instead of two aluminum-flashing housings, its shroud is made of one piece of standard 14″ aluminum flashing, rolled and riveted into a cylinder. Inside the cylinder are the Harbor Freight heat gun guts, another homemade sieve (Figure 7b) and an adapter which powers a small Amazon gearmotor turning yet another Wobble Disk. Its handle is a piece of 1″ dowel. To dump the beans, simply pick up the whole shebang and dump the beans into your favorite cooling apparatus. Intuitive!

Here’s a predecessor on Sweet Maria’s YouTube channel, before I discovered 14″ flashing.

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Figure 11. The ultimate easy-build DIY roaster, at long last?

X. EZ Wobble Disk Coffee Roaster (mid-2021)

This is my most recent (last?) roaster (Figure 11). It’s designed to be as easy to build and use as possible. I borrowed several functional parts from previous roasters: an unmodified Harbor Freight heat gun, a readily available 8-cup flour sifter (making my own was just too finicky), and a B+D screwdriver for a 5-1/2″-diameter Wobble Disk. There are no metal brackets to cut and bend, and the basic structure is made of plywood and 1″ wood dowels. The B+D screwdriver is now my go-to Wobble Disk spinner, thanks in part to its low price, high torque, and an intuitive way to turn the sifter shaft with an ordinary 5/16″ hex nut driver. It’s about as simple as it gets.

Here’s a video kindly posted on Sweet Maria’s website:

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Are We There Yet?

So, ten roasters later, what’s left to do? Well, the sifter and motor mounts could be prettied up a bit, for sure.  The small Amazon motors seemed to struggle with bean loads of more than about 10oz. But the B+D screwdrivers are very strong and not one has failed. Maybe Wobble Disk speed control? Add-ons like a thermocouple and timer to create a few crude profiles would be nice. But all these add up to more money, more parts, longer setup time, and more chances of error and breakdown.

Figure 12. All 22 homemade coffee roasters I’ve built over the past 15 years.

I’ll leave you with a composite photo of all 22 roasters (Figure 12) and this link to an expert’s guide to coffee degrees of roast:

And here are a few of my ‘build-anything’ recommendations, for whatever you’re making:

1. Collect stuff to build with for your entire life.

2. Don’t ever stop thinking and planning.

3. Espouse a “build and improve” philosophy.

4. Do something — even if it turns out to be wrong.

5. Be prepared to cheerfully fail — one of the best ways to learn.

6. Be prepared to scale back your goals somewhat, at least temporarily.


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Larry Cotton

Larry Cotton is a semi-retired power-tool designer and part-time community college math instructor. He loves music and musical instruments, computers, birds, electronics, furniture design, and his wife — not necessarily in that order.

View more articles by Larry Cotton


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