Last year my wife bought me a countertop coffee roaster, and I’ve been hooked on home-roasting coffee ever since. Lately I’ve also been roasting in our convection open, which works great for medium- to medium-dark roast. (I use the countertop roaster for light- to medium-roasted coffee.)
Here’s a typical oven roasting session. Prep the house by opening several windows, because this will generate quite a bit of smoke! I pre-heat the convection oven to 500 °F (260 °C), the max for our oven. I also have some baking stones in there to help maintain an even temperature.
Load a perforated baking sheet (~12 x 18 inch) with about 12 oz (350 g) of green coffee — today I’m roasting Sweet Maria’s GCX-5443, Ethiopia Gera Jimma Nano Challa Co-op, my current favorite for medium-dark roast.
Put the loaded roasting pan into the oven, and listen for “first crack” (when the first coffee bean audibly pops open). Usually that’ll be about 5:00 minutes for me. About a minute later, it’s time to rotate the pan–this helps the coffee roast more evenly.
Ten minutes or so into the roasting process, I’ll start to see a bit of smoke coming from the oven. At that point, it’s time to start checking the coffee every minute or so. I pull the pan out of the oven just before I think the beans look “done”, because they’ll keep roasting a bit more from their internal heat. I pulled this batch out after 11-12 minutes. (I forgot to check the time.)
Now comes the hardest part: getting the 500-degree coffee beans from the pan into a colander. Then I take this and another colander outside, and pour the beans from one colander into the other. This helps the beans air-cool quickly, and also releases most of the chaff. Once the beans are cool enough to touch, I put them into a vented container and let them cool completely.
For more information on roasting your own coffee, check out Home Coffee Roasting: Romance and Revival by Kenneth Davids.