Practising the dark arts

With an increasing number of home roasting machines on the market, we investigate whether the results justify the time and effort. Photo by Gary Smith

A simple bit of maths on the back of the envelope will tell you it makes little financial sense to buy green beans and the necessary equipment to roast your own coffee at home when so many good value, quality roasts are available online and in the shops. But as with many things, cost is really only part of the equation. Learning to roast your own beans at home can be great fun and will help you learn more about the amazing coffee-making process.

Not everyone agrees. “Roasting is a complicated process,” says Paul Bonna from Kaffeekommune. “It’s easy to make coffee brown, but it’s so hard to roast properly.” But while it’s true there are many variable to consider when roasting coffee – from bean size and density to drying times, drum speed and airflow – there’s nothing stopping the enthusiastic coffee consumer from trying it out for themselves. With the help of Tom Haigh, coffee roaster and head of green coffee at Climpson & Sons, we thought we’d put some of the latest machines through their paces.

That’s not to say Tom wasn’t sceptical. “I’ve always been somewhat torn by the subject of home roasting,” he says. “Having worked in the industry for a few years, I’m familiar with the difficulties and frustrations of flavour profiling when it comes to coffee roasting.”

Sourcing quality green beans from a local speciality roaster or a reputable supplier such as Pennine Tea & Coffee or Has Bean should be your first priority. After that, it’s a question of how to roast them. The most basic method is in a pan or wok (the lovely guys at Finca Café in Dorset sent us some detailed instructions on how to do this – see fincacoffee.co.uk/WOK.pdf). Coffee folklore has it that during his time as a prison officer, Steve Leighton of Has Bean would wok-roast coffee during lunch break, although it seems that’s a little wide of the mark. “I’m afraid it’s a case of Chinese whispers,” says Steve. “I did used to roast in a pan, but not for production. Production roasting was done on a baby 2kg Amber roaster.”

The main issues when roasting coffee are smoke and chaff, so wherever you choose to roast make sure there is adequate ventilation. Our first attempt at roasting was in popcorn popper and we got a crash course from Marco Arrigo, who has been roasting coffee in this way for a few years (we even interrupted him teaching at a coffee and Italian spirits masterclass at Bar Termini, Soho, so he could do so). The guys from Volcano Coffee Works gave us some green coffee to play with, a Tanzania Mondul AA, and some professionally roasted beans for comparison.

Initially, we were stunned by how simple the process was. We simply threw some green beans in the popcorn machine and switched it on. We managed to get the coffee to 205°C and well past second crack – while the roast was way past what we’d usually want, we were trying to see if we could get the machine to cut out, but it didn’t and we stopped the roasting before the coffee got really dark and oily. We managed to get it in the espresso machine and pulled a half decent shot, which we were very impressed by.

Test conditions

Buoyed by our experience, we took all our gadgets to Climpson’s Arch for some extensive testing. Tom chose a Musasa Dukunde Kawa Ruli from Rwanda to roast. “We’re aiming for a roast that’s even, medium-light and developed,” he explained. “I chose this coffee for it’s brightness, delicacy and acidity. It’s an accessible coffee to achieve a great flavour with, although it’s tricky to develop balance in the cup.”

In Climpson’s Loring, such beans take around nine minutes to roast. This is just past first crack – listen for the sound of snapping twigs as the beans heat up. If you continue to apply heat, the popping slows, then stops. Shortly afterwards a less prominent snapping – known as the second crack – can be heard. This is too far for most speciality coffees and produces a darker roast towards a French or Italian style.

Our aim was to get all our coffees to a similar level, 20% past first crack. The beans were to be judged on time and colour, and we’d finish the experiment with a blind cupping alongside the professionally roasted versions.

Popcorn maker

First up was a secondhand Prima PCM001 popcorn maker we picked up from eBay for £10. Tom’s initial thoughts on the machine were positive. “It’s very cool,” he said. “I love the compact design, accessibility, functionality and retro look – it looks like something you’d get after collecting tokens from cereal boxes. The sensory availability during the roast is also ideal thanks to the open top.”

We switched on the machine and allowed it to warm up for a few minutes before adding 50g of green coffee. Immediately, the coffee started swirling around the chamber and it looked like all the beans were moving freely. It was interesting to watch the colour and aromas gradually develop. But while having an open-top machine like this allows an unparalleled view of the developing coffee beans, it also allows a lot of chaff to blow into the air, so it may be best to use this machine outside or at least directly underneath an extractor fan.

Another benefit to working with an open top like this is that it’s easy to hear the first crack. We took the roast to five minutes, then tipped the beans on to a tray and shook it to cool them while blowing away as much as the chaff as possible.

Gene Café roaster

This is much bigger and more impressive looking than the popcorn maker. It has an off-axis rotating cylinder so the beans are never still, and hot air is pushed through the chamber to roast the beans as they tumble. The glass cylinder gives a good view of the beans. “The chaff collector and hot-air design also promised clean flavour potential in the coffee,” said Tom.

As with the popper, we ran the Gene empty to warm it up, but found removing the roasting chamber and filling it with beans quite cumbersome. “The fastidiousness of the design makes for a panicked and less-relaxing roast,” said Tom. By the time we got the beans in the chamber, the internal temperature had dropped more than 100°C.

This is a remarkably quiet machine: the electric motor that rotates the drum and clack of a steel grate inside are all you hear. On the downside, the chamber is so insulated we couldn’t easily hear the sound of the coffee cracking and we’re still not sure it ever got there. We ran two lots of beans through the machine, aborting the roast at 11 minutes the first time and using the machines specific “cooldown” phase on the second roast after nine and a half minutes. The machine can theoretically take up to 300g of coffee each time, although we only used 100g.

Ikawa home roaster

Many of you will have seen Ikawa’s new digital home coffee roaster at the London Coffee Festival or on Kickstarter. Now available for pre-order from £600, this is a seriously technical piece of kit. The roaster works with an iOS app so you can plot, perfect and save your roast profiles. Much of the tech has trickled down from the professional version, which has been celebrated by many leading figures in the coffee industry, including Morten Münchow of CoffeeMind. “I recommend my clients to use the Ikawa as a sample roaster because we can easily exchange roast profiles and be sure we evaluate coffees in the same way even over long distance,” he says.

Looking into the roasting chamber there is a striking resemblance to the popcorn roaster but there are some obvious differences when it comes to temperature control and air power, and the chaff is also collected in a separate jar.

Tom was evangelical about the Ikawa. “I love this machine,” he said. “It’s sexy and well designed. The app is a dream to use and opens innumerable doors of experimentation, and the roast profiles can be set beforehand, as well as changed during the roast. It ticks all the boxes.”

The Ikawa’s cooldown phase is also impressive, bringing bean temperature down very quickly to kill the roast.

Blind cupping

After testing the machines, we conducted a blind tasting of the results. On an aesthetic note, we were pretty impressed with the colour of the beans from all the machines.

The two roasts from the Gene Café were flat and lacking interest, with an absence of acidity and an overriding bakiness in the cup. There was a relative amount of sweetness as the coffee cooled, however, and some good body. It appeared that the Gene Café didn’t get heat into the beans quick enough, even with our attempts at preheating. If you want to roast a fair amount of coffee for espresso for friends and family this would probably do a very good job, but its strengths don’t lie in getting the brightness and clarity needed to make a good filter roast.

The popcorn machine was a surprise hit for Tom. “I was expecting underdevelopment and ‘greenness’ in the cup due to the speed of the roast, but the coffee was unexpectedly balanced,” he said. “I tasted clean, cherry-like acidity, good body and candied sweetness. All-in-all I was really impressed.” It felt like the popcorn maker had a lot of untapped potential.

The Ikawa did win, but not by much. It produced a winey, balanced and crisp coffee. Our best roast was juicy with red apple acidity and a hint of caramel, but was still a tad underdeveloped at seven and a half minutes. However, we know we’d be able to tweak this on future roasts – the level of control is amazing. The app is intuitive to use and as the machine becomes available you’ll be able to download roast profiles and share yours with other users.

All this control comes at a price of course, but if you want to take coffee roasting seriously – maybe with a view to a career in the coffee industry (commercial air roasters work in a very similar fashion) – this is the machine for you. However, if you’re looking for a bit of fun and to produce some outstanding coffee along the way while learning about bean development, it’s got to be worth picking up a secondhand popcorn machine. If you want to gain more control over the heat, dimmer switch hacks are available online. After some research, the Prima PCM001 seems to be the best (not the novelty duck-shaped one) but we didn’t test them all.