‘Actually Pretty Simple’: The Wild World of DIY Coffee Roasters

Coffee roasters are expensive and slightly intimidating, but they are also fundamentally simple machines. As startup costs increase, no wonder people are building their own.

Finn Mclean's hand-built coffee roaster. Note the vegetable steamer cooling tray. Courtesy of Spaceboy Coffee.

Coffee roasting is, at its core, a pretty straightforward process: Apply heat to green coffee beans until they turn brown and delicious. But there are numerous ways to go about that process, and every roasting company approaches it differently, and at a different scale. There are multinational companies cranking out coffee ’round the clock in huge batches; sleek, venture-capital-backed brands roasting Cup of Excellence-winning coffees on state-of-the-art machinery; micro-roaster setups in sheds and garages; and everything in between. 

A big problem for many hoping to start their own company is that commercial machines are expensive. To roast enough beans to make it a viable business, you’re looking at a big up-front investment—a 6kg Mill City roaster starts at nearly £20,000. Although secondhand is an option, and places like Aliexpress will sell you something that at least looks like a roaster for a couple of grand, it can still be out of reach for many.

For prospective roasters, one option is to save up, which could take years. Another is to find investment, which almost always comes with strings attached. But there’s a third option, especially if you’re thrifty and practical-minded: Why not just build one yourself?

Welding Knowledge Not Needed

Working for a large specialty coffee company in Bristol, Finn Mclean spent a lot of time taking roasters apart to clean them. He began to observe that coffee roasters are fundamentally basic machines—there’s a big drum, a motor that turns it, a heat source that heats it, some form of air flow, and a tray to cool the roasted coffee in. “They’re actually pretty simple”, Mclean tells me. “I started thinking, I reckon with my zero knowledge of engineering I feel like I could build a machine that’s based on one of these but like, just from stuff from B&Q and eBay”.

It’s not a completely absurd idea. There are plenty of instructional videos and how-to guides on the internet, although Mclean built his roaster from scratch with no guidance (he didn’t know there was a whole Instructables guide until I told him about it during our interview). There’s definitely a crossover between those who are interested in home coffee roasting and those who enjoy tinkering in their sheds (and possibly losing their eyebrows in the process). But building a machine capable of commercial roasting is a whole different challenge.

After a year of contemplation—and despite not knowing how to weld—Mclean slowly began to build a coffee roaster. The first iteration had a hand drill for a motor, with a guitar string wound around the trigger that would speed up the drill the tighter it was pulled, inspired by dads on YouTube making drill-powered go-karts for their kids. At first, he used a hair dryer for airflow, but that proved too powerful and was quickly replaced with a gentler centrifugal fan.

After tinkering with it while completing his master’s, Mclean and his half-built roaster moved to Edinburgh in 2020. That’s where the machine really came together. “I really hit the accelerator—I was in our kitchen sawing metal; I wanted to get the thing going, and after a year and a half the kinks were ironed out and it was working pretty reliably”.

At that point, it became a matter of making the coffee taste good. “Once those things were reliable and repeatable, it was just a matter of experimentation and keeping my process exactly the same every time—just changing one thing”, Mclean says. “I’m a chemist by training, so it was quite natural to me, the experimentation of it. It probably took me like six good months of experimenting before I was happy with how the coffee was tasting”.

Connection, Appreciation

Mclean launched Spaceboy Coffee in the autumn of 2021, and although he has since bought a traditional, factory-built machine—a 5kg Toper he found on eBay—he still likes using the DIY roaster. “I still slightly prefer the little machine, and I use it all the time”, he says. “The Toper turns out the house coffee and stuff but I just love using the little machine, I use it for all my expensive coffees”.

At one point, Mclean and a friend tried to build a bigger roaster themselves, but it turns out there’s a reason why manufacturers like Probat, Diedrich, and Toper exist. “Me and my pal Janis, who runs Ride & Grind, we actually built a 5kg machine together. We were using that for a good year or two until it had a major malfunction and we were like, ‘Okay, we need something more reliable than this.’ It turns out that the physics that are exerted on a 5kg machine versus my 1kg machine—it requires a bit more engineering than I currently have the ability to do”.

While much modern coffee roasting is high-tech—automated profiling software and internet connectivity, instantaneous gas and airflow changes—a skilled roaster still needs to be attuned to the process. This is something Mclean values: “I feel like I have a connection with my machines, you know? I definitely have more of an appreciation now that I’ve built one; it gives me more appreciation for the work I’m doing”.

Fire and Movement

It doesn’t get much more connected than roasting coffee over an open flame. Wood-fired roasters date back hundreds of years—the oldest working roaster still in use is a wood-fired Probat from 1896—while roasting over fire is a key part of the Ethiopian coffee ceremony. While wood-fired roasters are still used around the world today, they’re usually refurbished traditional machines. In the Pacific Northwest, however, one company is trying a different approach.

Although the company’s name is Campfire Coffee, actually roasting over a fire wasn’t originally the plan. Quincy and Whitni Henry were in the process of opening a coffee shop back in 2018, and reached out to numerous roasters in the Tacoma, Washington area looking to find a reliable supplier. Every one turned them down or never replied at all. “In hindsight, I get it—they probably got tens if not hundreds of customers putting in orders for multiple locations, and here’s a shop that isn’t even open”, Quincy Henry tells me.

The Henrys have always been outdoorsy—“We got engaged on a camping trip, our honeymoon was a camping trip”, Henry says—and this was going to be the theme of the coffee shop. But without a supplier, how could they open? Then Whitni’s sister threw out a suggestion: “‘You guys are always camping, you’re always cooking around a campfire—have you ever thought of trying to roast your coffee over a campfire? Because you just need a heat source right?’ And so I’m like, ‘Okay, we really don’t have much of a choice because all the roasters that we’ve reached out to and wanted to work with don’t seem interested’”.

Their first ‘roaster’ was a fire in their backyard and a popcorn shaker from Amazon, using green beans they found on some random website. “As you could imagine, it wasn’t very good”, Henry laughs. He had never roasted coffee before, so he did what many of us do when we need to figure something out: He went on YouTube. Eventually, he found something. “There was a video of a guy out in the jungle in Africa, it had to be from like the ’80s, and he had this big fire and he had a big drum and he was turning the drum and then he was dumping the coffee out onto this big tarp after it was roasted. I was like, ‘Okay, so it’s really just the fire and the movement of the beans—I think I can figure that out’”.

One of the differences between roasting with gas or electricity versus over a campfire is that the wood smoke can have a big impact on the final taste. Commercial machines have powerful fans to remove any smoke created by the beans, but anyone who has ever sat next to a campfire can tell you how hard it is to escape wood smoke. “One of the big things I've learned is how wood flame interacts with coffee”, Henry says. “You have some batches where the smoke does have a little bit of influence on the flavour profile—and that’s a good thing!—but sometimes it’s too much. And so the different wood types, the amount of smoke they put off, all of that factors in”.

After some feedback from a friend who had worked at legendary Seattle coffee roaster Caffe Vita—“she said, ‘I’ve had Ethiopians, but I’ve never had one taste like this before. I think you got something’”—the Henrys decided to really pursue this fire-roasting thing, and Campfire Coffee was born. But there were still a couple of things to figure out. As Henry puts it, “How do you do this in a way where the fire department’s not gonna shut you down?”

The customised popcorn shaker that started it all. Courtesy of Campfire Coffee

‘The Best Thing That Could Happen’

The pandemic-driven rise in home coffee brewing resulted in huge demand for Campfire’s beans, and meant that the company had to scale up quickly. The Henrys moved into a dedicated roasting space in late 2020, although it came with a neighbour who called the fire department on them. However, rather than being the end of Campfire, that brush with the authorities was actually a turning point.

“With the fire department, that was probably the best thing that could happen because they were like, ‘No, this is totally cool, you can do this, however we need you to make this into a proper firebox’”, Henry says. For safety reasons, it needed to be enclosed on both sides and have a lid. “So then we had to get a drum fabricated, we had to step up and make it a real thing”.

Because of growing demand, Henry had four roasters made, which meant he was able to go from producing a few hundred pounds of coffee per week to more than 1,000. “I had four of these little 10lb roasters going with these little fireboxes, and little homemade cooling trays that I had gotten the design off the internet or something. And we’ve been doing it like that until just recently, when we moved into another facility and got one big firebox made and a big drum, and that’s been like two years in the making”.

Campfire is now stocked in Trader Joe’s, among other retailers, and demand keeps growing; the company has shipped coffee as far as Japan. But Henry is particularly proud of the number of customers who have been buying from Campfire since the beginning. “We’ve had a handful that do kind of keep track of like, ‘Okay, you roasted this with fir and cedar, but when I first had this you roasted it over maple, and I can definitely tell the difference’”.

Sweet Spot

If you thought that roasting coffee over a fire would be tricky, you’d be right. With a factory-built, gas-powered roaster, a slight turn of a dial will adjust the heat being transmitted to the beans. Over the course of 10 minutes, an operator might make eight, nine, maybe dozens of tiny adjustments to control the exact amount of heat at the exact right time to ensure an even roast. 

With a wood-fired roaster? “I can control the flame, but not the same as a gas power, where you can just hit a knob or turn the electricity or turn the air off”, Henry explains. “I do have a choke mechanism for the flame but it’s still going to be really hot. Pretty quick, I learned that I had to throw any idea of consistency out the window—that’s why now everything I roast is just medium-dark, because that’s my sweet spot”.

The Henrys now have their coffee shop, as well as an outdoor gear library as part of their commitment to making the wilderness accessible to everybody. They fundraise for local summer camps, and hope to inspire the customers who visit their cafe to find a nearby trail or camping spot—and maybe take some wood-roasted coffee with them.

Here’s to the Roasting Renegades

While these sorts of self-built coffee roasters might not become widespread—as Mclean notes, once you try to build to a certain size it can be difficult, if not downright dangerous—they’re nonetheless an interesting subgenre of the coffee industry. Much of modern coffee roasting is quite removed from the elemental nature of the process, all fire and heat and chemistry. When you’re churning out roast after roast to meet orders, it’s not always possible to really connect to what you’re producing until you taste the finished product.

I’m a coffee roaster in my day job, and while I would never attempt to build my own machine—I would 100% blow myself up—there’s definitely something romantic about getting so close to the process. And that’s not to mention the democratisation and affordability that comes along with just doing it yourself.

The coffee industry can often feel dominated by those with cash to splash on the fanciest equipment. But roasting renegades like Henry and Mclean show us that it’s possible to create a successful coffee company using tools already at hand—and that anyone with a modicum of knowledge and a lot of bravery can build themselves a machine that creates delicious coffee.