How to Build a Coffee Roasting Machine

Build and operate your own roaster for full control over the color and flavor of the beans in your brew.

Photo by Jon Stika

Until the early 20th century, roasting coffee, like baking bread, was one of many common weekly household tasks folks did themselves. Much of the coffee was roasted in an open pan on top of a hot stove. The green coffee beans would be stirred as they popped and crackled, until they reached the desired degree of color and flavor. Later, as the nation recovered from the Great Depression, roasted coffee became more readily available, and home coffee roasting quickly faded away. But now, roasting coffee at home has been making a comeback as people strive to become more self-reliant and learn to appreciate a truly fresh cup of joe.

As in years past, home coffee roasting can be as simple as stirring beans in a pan over a heat source. However, roasting a batch of coffee beans still takes time. Manually keeping beans in constant motion for 15 to 20 minutes can be a bit tedious, and the process can generate enough smoke to set off smoke alarms.

In the years I’ve roasted coffee beans at home, I’ve gone through a progression of roasting devices with varying degrees of success. I began with a hot-air popper, which did a good job of roasting the beans but couldn’t handle extended use at high temperatures, and various electronic components would burn out and need to be replaced with regularity. Hot-air poppers also limit the amount of coffee that can be roasted at one time, so I needed to roast beans multiple times a week.

My next coffee roaster was a repurposed popcorn popper of the stovetop variety. It was a simple machine that I could heat with an electric or gas burner. It was reliable, and could handle up to a pound of beans at a time. The main drawback to this roaster was that I had to turn the crank that stirred the beans in the bottom of the pot for the time it took the beans to roast. Sometimes, turning the crank by hand seemed to take an eternity, so I developed a motor-driven coffee-roasting machine that would do the tedious part of the procedure for me! This liberated me so I only had to monitor the progress of the roast until the beans were ready to be dumped into a colander to cool.

To assemble this machine, I only needed to design a motor to turn the handle, since I already had an electric burner and the repurposed popper pot. Fortunately, I found a geared motor that turned at an appropriate speed (45 rpm), with a pulley radius that matched the radius of the popper’s handle rotation. This was perhaps the most critical component of my coffee-roasting contrivance, and it was available from American Science and Surplus.

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