Tired Of Popcorn? Roast Coffee Instead

We’ve seen a lot of coffee roaster builds over the years. [Ben Eagan] started his with a hot-air popcorn maker. If you think it is as simple as putting beans in place of the popcorn, think again. You need to have good control of the heat, and that requires some temperature monitoring and a controller — in this case, an Arduino. [Ben’s] video below shows how it all goes together.

With the Arduino and the power supply strapped to the sides, it looks a bit like something out of a bad post-apocalypse movie. But it looks like it gets the job done.

In addition to the Arduino, a thermocouple measures the temperature and that takes a little circuitry in the form of a MAX31855. There’s also a relay to turn the heater on and off. There are other ways to control AC power, of course, and if a relay offends your sensibilities you can always opt for a solid state one.

The only other wrinkle was the addition of an extra power supply so the fan could operate without the heater. There might have been some other ways to manage that, but power supplies are cheap enough and at least the strapped on power supply counterbalances the strapped on Arduino on the other side of the popper.

We’ve seen popcorn poppers used like this before, of course. Thermocouples are a great way to measure high temperatures, but there are lots of other ways to measure that particular quantity.

17 thoughts on “Tired Of Popcorn? Roast Coffee Instead

  1. I used a small variac to adjust the fan speed and a Omega temperature controller for the heating element. My Chinese solid state relay recently died and shorted closed. I knew it was an $8 fake and supposedly rated for 40 amps. It was potted nice enough inside and used a 16 amp triac! They were so close to actually building a decent copy. Guess I might splurge on the next Mouser order and get a legit $35 SSR.

    1. I do buy quite a lot of stuff including semiconductors from China, but i have a personal rule to not buy any power-related devices like SSR there and nothing that will be safety-critical like optocouplers that will be used in mains-connected stuff, fuses, … With this basic rule i off course had a few bad surprises but nothing dangerous at least. And to my big surprise all the AVR i bought and all the 74′ are fine at first look.

  2. Been home-roasting raw peanuts (thanks to nuts.com for bulk raw peanuts!) and it’s easy and surprisingly consistent in my toaster oven. Has anybody tried roasting by placing the beans on a tray in their toaster oven?

    1. The issue with coffee is the higher roast temperature at end of roast, and the need to stop the roast process at the desired temperature with minimal heat coast. If you roasted peanuts to french roast temps, I suspect they would be burnt in taste. Toaster ovens have been used and discarded as too difficult to control.

      Your peanuts stop roasting at a temperature below a “City” roast which many people do not like.

    2. The beans also need to be agitated/mixed to aid in achieving an even roast. I still prefer my drum roaster to any hot air blower-roaster. I have BBQ-roasted coffee in a cast iron pan while stirring frequently with the resulting roast having a broad variance.

  3. “You need to have good control of the heat, and that requires some temperature monitoring and a controller”

    I don’t doubt you are better off with these things than without. But do you “need” it? I knew a guy who roasted coffee beans in an air popper. I don’t remember it being modified with sensors or controllers though it was a long time ago. I think he just was well practiced and had done the experimentation to know just when to stop. He made good coffee, I’m no connoisseur but I’m confident saying it was better than anything I tried that was store bought and certainly better than that burnt motor oil that sells so well at Starbucks.

    I’m just saying.. it’s a nice build but don’t discourage anyone who isn’t ready to make the same effort!

    1. I agree with this! Making any coffee yourself is awesome, and not modifying the popper at all will still deliver some good coffee and fun results. What temp control gives is the ability to roast “profiles”. Holding your beans at specific temperatures is supposed to bring out different flavours. So even if the beans are exactly the same shade of brown in the end, they can taste very different.

      In other words, in the end, it was really about the colour of the bean, but rather the duration of chemical reactions we met along the way!

      1. I’ve been roasting coffee for 7 or 8 years, about 70 lbs a year. I started with an air popper. I don’t see the point of such an elaborate setup, especially when you’re roasting such a small amount. A popper has to be constantly monitored and shaken nearly the entire time. It’s done somewhere between the beginning of first crack and the first few seconds of second crack. My current roaster has a lot more settings than a popper, but I still go by ear and nose for when to stop it.

    2. “and certainly better than that burnt motor oil that sells so well at Starbucks.”

      An apropos definition of their product!

      (of course, if they made their coffee properly, people wouldn’t spend so much on additives (sugar, cream, flavorings) to hid the hideous taste)

  4. Suddenly a wild thought appears… so if coffee roasts at similar temps that popcorn pops, could one twist up some coffee beans and 3 or 4 kernels of corn in some tinfoil, yeet it into the campfire and yoink it out when you hear the popcorn pop???

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