Coffee Shop
Transform an old air popcorn popper into a coffee bean roaster controlled by a Raspberry Pi and a slick user interface.
Roasting beans in a repurposed air popper
Lead Image © studiostoks, 123RF.com
A quest for delicious coffee led me to roasting my own coffee beans at home. Using fresh-roasted coffee beans produces coffee that is considerably better than even the most expensive commercial coffee. The home roasting process only requires two things: heat and a mechanism to keep the beans moving. The beans must be agitated so they are not burned when exposed to the heat. One device commonly used by home roasters is an air popcorn popper, which simply blows hot air into a chamber. The popper is ideal because it roasts the coffee beans and circulates them at the same time.
Coffee starts out as a green bean (Figure 1). Heat is applied over a period of 7 to 15 minutes to produce roasted coffee. The roasted coffee bean can reach temperatures close to 500°F (260°C). If the beans are roasted too fast, however, they can burn, imparting some unsavory flavors to the coffee.
The Setup
To get started, I visited a nearby thrift store, which resulted in the purchase of two identical Presto PopLite poppers for a total of $8. I began to use one popper immediately without modification. It roasted the beans in less than five minutes, which is too fast, so I began unplugging the popper for 30-second periods to slow the roasting process. This process grew tiresome quickly, so I extracted the fan and heater assembly from the second popper and added a thermocouple, an AC relay, some LEDs to simulate a flame, and a Raspberry Pi (Rasp Pi) to create the Electric Lights and Fire (ELF) coffee roaster (Figures 2 and 3). The smoke stack on ELF is the roasting chamber, and this is where the coffee beans are placed for roasting. Video of the ELF in action exists on my blog [1], and all the source code is available in a Bitbucket archive (see the "Downloading Source Code" box).
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