How to Build a Coffee Roaster from a Popcorn Machine

If you’ve ever wondered whether you can roast coffee beans without dropping hundreds on a pro machine, here’s proof you can start small—really small. One coffee enthusiast did just that, converting a cheap popcorn machine into a functional coffee bean roaster with surprising results.

The answer is yes, you can build a working coffee roasting system using a $90 popcorn machine, an Arduino controller, a temperature sensor, and a few other parts. The system achieves a temperature control accuracy within ±1.7°C, enough for home roasting experiments.

What’s in the DIY Coffee Roaster Kit?

The core of the build is a small popcorn machine purchased on Taobao for around 90 yuan including shipping. The stock plastic wind guard melted at temperatures over 200°C during testing, so it was replaced with a homemade aluminum foil shield. Temperature control is handled by an Arduino Mega controller (though a smaller Micro version would suffice), paired with a temperature sensor module and a relay module to manage the heating element. A stainless steel bowl—purchased from Muji for 100 yuan—is used to collect the chaff, or “silver skin,” that separates from the beans during roasting.

How the Roasting Process Works

About 50g of green coffee beans are loaded into the machine’s drum, covering the bottom air vents. Heat from the popped air jets roasts the beans. A thermocouple probe monitors internal temperature in real time. Initial tests showed a temperature curve with a fast initial rise and a final cool-down phase (not shown), with the observed temperature hovering close to the target. The orange line represents actual temperature while the black is the set point; the maximum deviation recorded was around 5–6°C, later refined to ±1.7°C after calibration. The roast is controlled via custom curves programmed into the Arduino, developed after two days and more than 500g of test roasts.

Results and Roast Profile

The first successful batch produced 45g of coffee roasted to a level between city and full city roast—a preferred profile by the maker and their spouse, who find Starbucks-style dark roasts overly bitter. The roasted beans still carry some yellowish silver skin, which needs to be removed by hand. The roasted coffee should rest for 6–24 hours before brewing, and tastes best within 72 hours of roasting. This DIY system, currently in “Mark I” form, is set for future aesthetic improvements—including a new casing made from a Korean chili sauce box.

Frequently Asked Questions

Can I really use a popcorn machine to roast coffee beans?

Yes, with modifications. A basic popcorn machine can function as a coffee roaster if you replace parts that can’t withstand high heat, like the plastic cover, and add proper temperature control using sensors and a relay. This project proves it works with a $90 machine.

What temperature range is needed to roast coffee?

Coffee roasting typically starts around 180–200°C and can go up to 230°C depending on the roast level. In this project, temperatures reached above 200°C, and the system needed an aluminum shield to prevent melting.

How accurate is the temperature control in this DIY roaster?

The temperature control is within ±1.7°C (k=2) after refinement. Initial tests showed deviations up to 5–6°C, but the Arduino-controlled setup eventually achieved consistent and usable accuracy for home roasting.

What kind of coffee beans can you roast with this setup?

This setup can roast any green coffee beans, including single origins like Yirgacheffe or blends. The maker tested with Colombian beans and recommends resting the roasted batch 6–24 hours before brewing for best flavor.

Is the Arduino controller necessary?

An Arduino (or similar microcontroller) is not strictly necessary but enables precise temperature control through programmed roast curves. Without it, you’d have to manually control the heat, making consistency much harder to achieve.

How long should roasted coffee rest before brewing?

Coffee should rest for at least 6–24 hours after roasting to allow CO₂ to degas. The optimal flavor window is within the first 72 hours post-roast.

Recommended FrontStreet Coffee for Home Roasting

Try FrontStreet Coffee’s Ethiopia Humbera for bright floral and citrus notes, or their Yirgacheffe for juicy berry and stone fruit complexity—both ideal for experimenting with light to city roast profiles. Their Colombia beans also respond well to medium roasts, balancing nutty and caramel tones. Freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.