Picture of Sumiyaki Roasting Machine at Sapporo Coffee Kan, 30kg Capacity (Largest in Hokkaido as of 2026)
Introduction
I had the opportunity to present Sumiyaki coffee at local events such as Coffee Fest, I often explain about Sumiyaki coffee — how using charcoal instead of gas or electric to roast the beans gives the coffee its rich aroma.
The key difference is the type of heat. Charcoal produces far-infrared rays that penetrate deep into the beans and cook them from the inside out. Because of that, the overall roasting temperature can be kept lower than gas — the infrared is doing the heavy lifting from within the bean, not just scorching the surface.
Difference in temperature between gas and charcoal coffee roasting
And whenever I explain this — especially to people who are into specialty coffee or roasting themselves — the same two questions always come up:
"Okay, but how is the Sumiyaki machine actually different from a regular gas roaster?"
And:
"How does the heat actually reach the beans? A gas roaster has a drum with the flame right underneath it. So where does the charcoal even go?"
Good questions.
I decided to write this up properly with the help of Japan's renowned Charcoal Roasting Master, Mr. Ito, President of Sapporo Coffee Kan.
I had fun writing this — I hope you enjoy it!
Roasting with Sumiyaki Coffee Roaster
I will go deeper later in the conversation, but here is a video of the actual Sumiyaki Roasting Machine used at Sapporo Coffee Kan (our coffee).
videoid="ykGO7pYVfMw"
The capacity is 30kg (66 lbs), making it the largest sumiyaki machine in Hokkaido as of 2026. Such capacity is required as Sapporo Coffee Kan proudly serves the coffee at Hokkaido Airline (AIR DO) and all 11 cafes, including the popular cafe in front of Sapporo Clock Tower (read about Sapporo Coffee Kan here)
Mr. Ito says,
"Just because the drum holds 30kg doesn't mean we fill it to 30kg. Load it that full and you'll end up with uneven roasting. So we keep it to around 20kg maximum per batch." (３０ｋｇの容量があるからといって３０ｋｇの生豆を投入しますと
He continues,
"Each roast takes about 20 minutes on average — but it's never exactly the same. Outside temperature makes a real difference.
A cold winter morning and a hot summer day will heat up the chamber very differently at the start.
And because this is direct-fire roasting, there's also the risk of ignition from the natural oils in the beans and the silver skin （銀皮）— the thin papery chaff that separates from the beans during roasting.
This is why the daily roasting schedule is so important.
Every batch requires full attention."
He gives us an example of how a typical day is planned out:
"We start when the temperature is still low, so we begin with smaller batches and lighter roasts first.
Then, as the chamber warms up, we move into the larger batches and darker roasts.
Toward the end of the day, we gradually work back to lighter roasts again — slowly bringing the heat down, little by little, until the charcoal fire is finally put to rest."
He adds,
"Every roast runs at over 200°C (392°F), and we're checking the roast level in seconds — not minutes.
So the moment the beans come out into the cooling tray, two things happen immediately: we cool them down as fast as possible, and we check for any foreign material mixed in."
"The cooling step is more critical than people realize. If you don't cool the beans quickly, the residual heat keeps cooking them — and what you intended as a medium roast quietly becomes a dark roast. All that work, and the beans just keep going without you."
He also mentions something most people never think about:
"When you're roasting at these temperatures, the smoke can't just go straight outside — that causes all kinds of problems.
So we route it through what's called an afterburner, which burns off the smoke before it's released.
It's not glamorous, but it's important."
Afterburner to burn off smoke before releasing it to the environment.
Whenever he talks about coffee and coffee roasting, his eyes are different. You can feel the passion in every word — and honestly, you can taste it in every cup too.
Miki visited to meet Mr. Ito in 2025 winter, and she came back saying the same thing everyone says after meeting him: you just can't fake that kind of dedication.
Miki with Mr. Ito (Right) and Mr. Sugimoto (Left) at Sapporo Coffee Kan
What is “Sumiyaki” Coffee?
In case you are confused, let me explain what Sumiyaki Coffee is.
In Japan, sumiyaki (炭焼き) coffee roasting uses actual charcoal as the heat source instead of gas or electricity.
Sumiyaki (literally “charcoal grill”) roasting is a time-honored art – it requires skill to manage the fire and airflow (as you can see from Mr. Ito's comments above) so the beans roast evenly at the right temperature.
The result, however, is a uniquely rich and aromatic coffee.
Charcoal-roasted beans are often described as having a sweet, savory flavor balance with a full-bodied richness that many coffee lovers find unparalleled.
Modern Sumiyaki roasting machines are basically a marriage of old and new — charcoal heat combined with drum roaster technology. Ancient technique, precise engineering. The result is a roasting process that's part science, part craftsmanship. And you can taste the difference.
Binchotan Charcoal Fuel: Clean, Intense Heat Without Smoke
Sumiyaki roasters typically burn binchōtan (備長炭), a type of high-grade Japanese oak charcoal renowned for its clean, long-burning heat.
Binchotan logs (see image above) burn extremely hot and produce far-infrared radiation without adding smoky impurities.
In fact, quality binchotan (like the ones we use) contains very little moisture or resin, so it combusts with almost no flame or smoke once lit.
This means all that energy goes into heat and infrared radiation, not into steam.
Have you had charcoal grill dish like Yakitori (焼き鳥) or Yakiniku (焼肉)? Same concept there. Less moisture in the meat, crisp outside, soft inside.
The charcoal’s steady infrared output “cooks” the coffee beans evenly from the inside out, giving a deep roast without charring the outside. The lack of moisture in the fuel also improves heat transfer efficiency.
The downside?
Binchotan is hard to ignite and takes expertise to manage – roasters often use a small gas burner or blowtorch to get the charcoal glowing, and then carefully control it (sometimes even fanning by hand) to maintain consistent temperature.
It’s more expensive than regular charcoal, but it lasts 2–3 times longer and yields a syrupy, smoky, but not burnt flavor in the coffee.
In short, binchotan is the powerhouse behind sumiyaki’s famously robust yet clean roast character.
Infrared Heat from Charcoal Roasts the Beans from the Inside Out
One big difference with charcoal roasting is how the heat penetrates the coffee.
When binchotan charcoal burns beneath the rotating drum, it emits infrared (IR) and far-infrared rays that deeply penetrate the coffee beans.
Think of how a charcoal grill cooks food – the radiant heat can cook through to the center.
Gas Roasted Coffee Beans vs Charcoal Roasted Coffee Beans
In a sumiyaki roaster, this infrared energy heats each bean from its core, while the hot air from the fire simultaneously toasts the bean’s surface.
In effect, the beans are roasted from both the inside and outside at the same time.
This dual heating is gentler on the coffee’s surface and helps avoid the problem gas burners often face – a scorch on the outside while the inside lags behind.
Because the charcoal’s IR can cook the interior, the roaster doesn’t need to crank up the external temperature as high as a gas roaster might.
The result is a more uniform roast at slightly lower environmental temperatures, which preserves more of the bean’s aromatic compounds.
Roasters describe the finished beans as plump and evenly roasted throughout – no scorched exterior, and no undercooked center.
This is a key reason sumiyaki coffee often has a very balanced, mellow flavor despite being very full-bodied: the chemical reactions inside the bean develop thoroughly without the bitter char of a too-hot surface roast.
Perforated Drums Let Radiant Heat Surround Every Bean
To take advantage of that infrared heat, Japanese charcoal roaster machines use a special drum design.
The roasting drum – essentially a metal cylinder that tumbles the beans – is made of punch-perforated steel (パンチングボード) rather than solid metal.
Thousands of small holes (about 4 mm in diameter, totaling ~30% of the surface area) are punched in the drum’s walls.
Here is a picture of the drum inside the roasting chamber, viewed from below.
A Picture of the drum inside the roasting chamber, viewed from below
This perforation allows the IR radiation and heat from the burning charcoal to pass directly into the drum and reach the beans.
In many gas drum roasters, the drum is solid or has fewer perforations, and the heat transfers mainly through the hot metal surface and convective air — not through direct infrared radiation like charcoal does.
The sumiyaki drum effectively acts like a mesh, bathing the coffee in direct heat. As beans tumble, they get evenly exposed to the charcoal’s radiant glow and hot combustion gases flowing through the holes.
The perforated drum still provides plenty of conductive heat (it gets hot, too), but it mainly serves to evenly mix the beans while letting the charcoal heat envelop them.
This design is akin to older “direct-fire” roasting drums – in fact, many small traditional roasters in Japan also used perforated drums with a gas flame directly underneath.
The sumiyaki roaster follows that direct-fire heritage, but using charcoal as the flame.
A Picture of Roasting Drum with mesh drum (view from the front)
The result is an efficient heat transfer: every coffee bean is surrounded by infrared-rich heat for a thorough roast.
Of course, the roaster must keep those holes clear of chaff and debris, so many machines allow the drum to open for cleaning (some designs have a drum that splits open for maintenance).
But as long as it’s clean, the punching metal drum ensures no bean is hiding from the heat. This is crucial to achieve the even, deep roast that sumiyaki coffee is known for.
A Picture of Roasting Drum with mesh drum (view from the front - Zoomed Out)
Gas Burners Are Used Only to Ignite the Charcoal, Then the Charcoal Takes Over
Interestingly, a charcoal coffee roaster isn’t 100% off-grid – most have a small gas burner built in, but it's purely to get the charcoal started.
At the beginning of a roast, the operator will load the firebox with pieces of charcoal and use a propane or city-gas flame to ignite them.
Once the binchotan logs are glowing red-hot, the gas is turned off, and all the roasting heat comes from the charcoal itself.
In essence, the machine behaves like a supercharged traditional charcoal grill from that point on.
The charcoal bed provides steady heat throughout the roast, typically without supplemental gas. (In fact, some purist roasters insist on turning off the gas as soon as possible to ensure the coffee truly roasts “over charcoal.”)
Because you cannot instantly throttle a charcoal fire the way you can adjust a gas knob, the roast master must skillfully manage the fire ahead of time.
This involves choosing the right amount of charcoal and timing the ignition so the coals hit peak heat at the desired stage of the roast.
Binchotan Charcoal (Sumi)
Some modern sumiyaki roasters do include automated controls for the airflow or have a small adjustable electric/gas heat source as a backup, but generally the charcoal’s natural heat provides the roast profile.
This approach demands experience – controlling a live coal bed is trickier than turning a dial, which is one reason sumiyaki roasting has a high learning curve.
Nonetheless, the flavor payoff and the romantic appeal of roasting on coals make it worth it.
Many roasters also believe the gentle, omnidirectional heat of the charcoal yields a roast that’s difficult to replicate with any other fuel.
Dampers Regulate Airflow to Control Heat and Roast Profile
If you peek at a sumiyaki roaster, you’ll notice levers or knobs for airflow dampers.
Managing airflow is the primary way to fine-tune the roast temperature in a charcoal system (since you can’t quickly raise or lower the charcoal flame itself).
Opening the damper increases the amount of air drawn through the roaster, feeding the charcoal more oxygen and also pulling more hot air through the drum.
This can boost the roast intensity and temperature. Conversely, closing down the airflow damper will choke the fire slightly (reducing its heat output) and keep more heat and smoke inside the drum, slowing the roast.
Skilled roasters constantly adjust these dampers during the roast to hit target temperatures at key milestones (like drying phase, first crack, etc.).
Essentially, the damper is the “heat control dial” for a charcoal roaster – much like gas pressure is for a gas roaster.
The airflow also affects bean flavor development: More airflow can increase convective heat transfer for a faster, brighter roast, while less airflow yields a slower roast that may develop more body.
Too much airflow can strip away moisture and lead to a sharper profile, whereas too little can cause smokier flavors as smoke lingers.
Therefore, sumiyaki roasters must balance the damper to manage heat and also vent out smoke appropriately.
In modern machines, an exhaust fan pulls the air; the damper (a movable plate or valve in the duct) lets the roaster precisely control how much air goes through the drum.
Mastering the damper is part of the craft – it’s one of the key tools to ensure the charcoal roast turns out neither underdeveloped nor burned.
Afterburners Burn Away Smoke and Odor for a Cleaner Roasting Operation
Roasting coffee produces a lot of smoke, and charcoal fires can add even more smokiness.
To keep the roastery (and neighbors!) happy, many commercial sumiyaki roasters include an afterburner.
This is a secondary combustion chamber or catalytic converter in the exhaust system that incinerates the smoke and volatile compounds coming off the roast.
For example, Sapporo Coffee Kan’s new 30 kg charcoal roaster is equipped with a special afterburner mechanism that eliminates excess smoke and unpleasant odor.
Afterburner to burn off smoke before releasing it to the environment.
As the exhaust air leaves the drum, it passes through a high-temperature burner or catalyst which burns off the smoke particles and oils, drastically reducing visible emissions.
Afterburners are common in large gas roaster setups too, but they are especially useful for charcoal roasters, which can produce a heavy campfire-like smell otherwise.
By cleaning the exhaust, the afterburner not only reduces pollution but also prevents the roasted coffee from picking up any acrid smoke flavors.
The use of afterburners means a sumiyaki roaster can operate in urban environments or indoors without smoke complaints.
It’s a modern technological addition that makes traditional charcoal roasting viable on a larger scale.
Some roasters also point out that binchotan charcoal itself is very clean-burning (producing minimal smoke once fully lit), so the afterburner mainly tackles the coffee bean smoke.
Either way, this feature ensures that all you smell is the sweet aroma of roasting coffee – not a bonfire – when you visit a sumiyaki roastery.
Batch Sizes and Roast Duration: Big Drums, Smaller Loads
Charcoal roasters come in various sizes, but a typical commercial machine might be rated for around 30 kg of beans per batch.
In practice, roasters often fill about two-thirds of that capacity (for example, ~20 kg in a 30 kg drum) to allow good airflow and bean movement.
The extra headspace helps the beans roast evenly, as too large a batch can trap heat or lead to inconsistent results.
Even with real coal as the heat source, the roast times aren’t much different from conventional roasting.
A medium roast usually takes on the order of 15 to 20 minutes in a sumiyaki roaster, similar to the timing on a gas drum roaster.
Side view of the sumiyaki roaster - the bottom part is where charcoal goes in
The process begins with a gentle drying phase (as moisture in the green beans is driven off), then ramps up to first crack (around 8–10 minutes in, depending on batch and heat), and then development until the target roast level is achieved.
Charcoal’s high steady heat can actually accelerate the roast if not carefully controlled, so experienced roasters watch the bean temperature closely.
Many will start with dampers more closed (to build heat slowly), then open up near first crack to avoid stalling, and adjust as needed to hit a total roast time near that 15–20 minutes sweet spot.
Because the charcoal bed holds heat so well, it’s also possible to do back-to-back batches once it’s going – the second batch may roast a bit faster as the roaster is fully heated.
Modern sumiyaki roasters often have temperature probes and data logging, just like gas machines, to help the operator repeat profiles.
Still, there is a hands-on aspect; you’re guiding a live fire, which makes each roast feel a bit special.
Capacity-wise, these machines are generally used by small to mid-size roasteries – a 30 kg charcoal roaster is considered “large” in this category. (For comparison, industrial gas roasters can be 60–120 kg per batch or more.)
The batch sizes are inherently limited by the need to manage an open charcoal flame and ensure safety.
But within those limits, sumiyaki roasters produce enough volume for a busy specialty coffee shop or a small coffee chain, all while maintaining artisanal control over each roast.
Rapid Cooling Prevents Over-Roasting Once Beans Are Done
Just like any roasting method, charcoal-roasted coffee must be cooled immediately after it’s dumped from the drum.
In fact, cooling is especially critical in sumiyaki roasting because the beans themselves may be extra heat-saturated (having been cooked from the inside) and the environment of the roaster is very hot.
If beans were left to sit, they would continue to “coast” and could easily over-roast or scorch.
Sumiyaki machines usually have a large cooling tray with arms that stir the beans while a fan pulls ambient air through them. Once the roast reaches the desired level, the operator opens a hatch and the freshly roasted beans rush out into the cooling tray (often with a dramatic plume of smoke and chaff).
Powerful fans suck air through the beans, dropping their temperature from over 200 °C down to near room temperature in just a few minutes.
This rapid cooldown halts the roasting process in its tracks, effectively “locking in” the flavor profile that was achieved.
It also helps vent out residual smoke and chaff. Some charcoal roasters incorporate an air shaker or air shooter after cooling – essentially blowing the cooled beans to remove any remaining chaff – ensuring only clean, glossy beans make it to storage.
The importance of quick cooling is universal in coffee roasting, but with charcoal there’s an added twist: the equipment remains very hot and radiates heat, so even after beans exit the drum, they could singe if not cooled and moved away.
A good cooling system, therefore, is part of what makes modern sumiyaki roasters effective. In fact, many machines recycle the hot air from cooling into the afterburner or chimney (an efficiency trick borrowed from other roaster types).
The bottom line is that once you’ve got that perfect charcoal roast, you want to chill those beans ASAP – preserving the nuanced flavors and avoiding any bitter overdeveloped notes.
Different Types of Sumiyaki Roasting Machines
Though I have been explaining one type of Sumiyaki Roasting Machine that we (Sapporo Coffee Kan) use, there are a couple of different types of Sumiyaki Roasting in Japan.
Here are illustrations of three common Sumiyaki Roasting Machine Types. (a) in the picture below (Direct Heating) is what you have been reading about and what we use.
Type (b) — the semi-hot air type — uses the same basic drum structure, but without the punched holes in the metal. That one small difference changes how the heat reaches the beans.
And (c), the hot air type, works completely differently. The heat source isn't directly beneath the drum at all — it's positioned separately, and hot air is blown in, almost like a giant hair dryer. This is the type used by large commercial roasters who need to process high volumes at a time.
Of the three, type (a) — the direct-fire type — is by far the most difficult to master. The variables are constant, the margin for error is small, and it demands full attention from start to finish. But when it's done right?
It produces the best Sumiyaki coffee.
That challenge is exactly why Mr. Ito chose it — and why the result tastes the way it does.
Charcoal vs. Gas vs. Hot-Air Roasting – How Do They Differ in Flavor and Technique?
Now that you have an idea about Sumiyaki Roasting Machines, let me explain from an angle of gas vs charcoal roasting.
All coffee roasters aim to turn green coffee into delicious brown beans, but the heat source and roasting style can impact the flavor and the roasting experience.
Charcoal roasting vs Gas: The most obvious difference is the presence of far-infrared heat in sumiyaki charcoal roasting, versus its absence in standard gas roasting.
In a gas drum roaster, the beans are mostly heated by the hot drum surface and hot convective air, which warm the outside of the bean first.
Reaching the core of the bean can be a challenge, so roasters sometimes compensate with higher temperatures or longer roast times – which can risk over-roasting the exterior of the bean.
This is why very dark gas-roasted coffee can sometimes taste flat or ashy: the outside got burnt before the inside developed, destroying some flavor compounds.
Charcoal’s infrared heat, by contrast, penetrates and cooks the inside, allowing a fully developed roast at a slightly gentler overall temperature.
In terms of flavor, charcoal-roasted coffee often has a distinct charcoal aroma, described as a toasty, sweet smokiness that gas-roasted coffee doesn’t have.
Gas roasting typically yields a “cleaner” taste – especially at lighter roast levels – because there’s no direct contact with smoke.
However, gas roasters can produce smoky or roasty notes too if chaff burns on the drum or if the roast goes very dark.
Charcoal roasting tends to neutralize some acidity in the coffee; experts note that charcoal ash is alkaline and can subtly reduce the acidity in the bean, leading to a smoother, rounder flavor profile.
Gas-roasted coffee may retain a bit more bright acidity (again, noticeable in lighter roasts).
Hot-Air (Fluid Bed) roasting vs Charcoal
Hot-air roasters like fluid bed machines (or modern recirculating roasters) work purely by convection – a stream of hot air suspends and heats the beans.
This produces a very uniform roast and avoids any contact with metal surfaces or flame.
The cup profile from hot-air roasting is often described as brighter and cleaner, emphasizing the coffee’s origin characteristics with less “roast” flavor imprint.
In terms of scale and day-to-day operation, each method has its own tradeoffs.
Gas drum roasters are the industry standard for a reason — they're precise, easy to control, and come in every size imaginable. If you want to turn a dial and get a consistent result, gas is your friend.
Hot air roasters are great for consistency too, and they're efficient. But a lot of roasters feel the cup comes out a little too clean — bright and clear, but missing some of that deeper body and sweetness you get from a drum roast.
Charcoal roasters are in a different category entirely. They're smaller, harder to manage, and honestly, more work. You're dealing with a live fire, not a dial. But that's also the point. The roasters who choose charcoal aren't looking for the easiest path — they're after a flavor that's just difficult to get any other way.
It's a bit like barbecue, honestly. A gas grill gets the job done. But if you've ever had something cooked low and slow over real charcoal — you know the difference.
Conclusion
If you've made it this far — thank you. This ended up being a longer article than I planned, but honestly, it's hard to talk about Sumiyaki coffee without going deep. There's just so much to it.
The short version is this: charcoal roasting is harder, slower, and more demanding than gas or hot-air roasting. It requires skill that takes years to develop, attention that never switches off, and a genuine love for what you're doing. Mr. Ito has all three.
Every cup of our coffee carries that.
The far-infrared heat, the binchōtan charcoal, the carefully planned daily roasting schedule, the rapid cooling — none of it happens by accident.
I love that we get to share this story with you. And I hope the next time you brew a cup of our coffee, you think about the fire behind it.
As always, if you have any questions, feel free to reach out. We'd love to hear from you.
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About the author
Kei Nishida
Author, CEO Dream of Japan
Certification: PMP, BS in Computer Science
Education: Western Washington University
Kei Nishida is a passionate Japanese tea and coffee connoisseur, writer, and the founder and CEO of Japanese Coffee Co. and Japanese Green Tea Co., both part of Dream of Japan.
His journey began with a mission to introduce the world to the unparalleled quality of Japanese green tea. Through Japanese Green Tea Co., he established the only company that sources premium tea grown in nutrient-rich sugarcane soil—an innovation that led to multiple Global Tea Champion awards.
Building on this success and his passion for Japanese craftsmanship, Kei expanded into the world of coffee, pioneering the launch of Japanese Coffee Co., the first company to bring Sumiyaki charcoal-roasted coffee to a global audience. His dedication to authenticity and quality ensures that this traditional Japanese roasting method, once a well-kept secret, is now enjoyed worldwide.
Beyond tea and coffee, Kei has also introduced Japan’s legendary craftsmanship to the world through Japanese Knife Co., making handmade katana-style knives—crafted by a renowned katana maker—available outside Japan for the first time.
Kei’s journey continues as he seeks out and shares the hidden treasures of Japan, one cup and one blade at a time.
Learn more about Kei
