We’ve always been intrigued by the idea that roasting coffee beans at home could be as simple as calling for an air popcorn popper, a method embraced by DIY diehards.
Air poppers use a fast-spinning vortex of very hot air (just under 500 degrees) to agitate the popcorn kernels so that they heat evenly and don’t burn—conditions that in theory should make these gadgets ideal for quickly roasting green coffee beans. (Green coffee can be purchased online, or even from your local barista.) We dug out one of our air poppers to give it a try and were amazed by how easy it was—and how much we liked the results—once we learned to follow these guidelines.
PROPER VENTILATION IS ESSENTIAL
Roasting coffee emits smoke, so if you don’t have a vent, consider roasting next to a window fan or on a porch (but not on a cold day, which can prevent proper heating of the beans).
The amount of coffee that you can roast in an air popper is small—usually about 1/2 cup.
CATCH THE CHAFF
As the beans roast, a thin, papery outer membrane (chaff) will slough off. Place a bowl beneath the popper chute to catch it or orient the popper chute next to the sink.
WATCH THE TIME
Roasting will take anywhere from 3 to 7 minutes, depending on how dark you like your coffee. Since beans will continue to darken even after you remove them from the popper, stop roasting just before they reach the desired color.
LISTEN FOR "CRACKS"
After about 3 minutes, the coffee beans will emit a loud “first crack,” an indication that they’re at the “light roast” stage. A minute or two later they’ll be at “medium roast.” At about the 6-minute mark, the beans will emit fainter, more tinny “second crack” sounds (the “dark roast” stage). If you haven’t already done so, take them out immediately, before they burn and turn bitter.
Dump the beans into a metal colander that’s been chilled in the freezer and then agitate them quickly until they are just warm to the touch.
LET THEM REST
The beans will taste better the next day as the flavor develops. Freshly roasted beans also emit a lot of carbon dioxide, so wait at least 12 hours before transferring them to a sealed container.