Roasting coffee in the oven is easy and often produces fine results, sometimes as good as those from commercial roasters. All you need is a little creativity and some green coffee beans, easily purchased from many companies online.
Making an Oven-Roasting Pan
An old pie pan works well for oven-roasting (a new one works, too, but it will be destroyed for pies) to convert into a roaster. First, the pie pan has to be holed – lots of little holes in it – with a hammer and nail. A drill bit also works, but low-tech or high-tech, the pan needs ventilation.
The ventilation is so that the beans will roast more evenly.
Using the New Roaster
Coffee beans roast at or above 450º, but it usually works better to start closer to 475º or 500º. Each oven is different, so taking careful notes for each roast and type of bean will ensure better results later on. Convection ovens give a superior roast, but also essentially work to raise the temperature, so with a convection oven, start the roast at 475º when learning.
One layer of beans is enough for oven roasting – more than that and the beans will receive different degrees of roast, and the yield will show too many color variations.
Roasts in the oven take anywhere from 8-12 minutes and the pan needs to be shaken gently at least once during the roast. There’s no sure-fire way to get a completely uniform roast in the oven, but by shaking once or twice, most of the beans turn and maximum uniformity can be achieved.
Tips for Roasting in the Oven
Un-monitored beans can quickly over-roast. A coffee-roast begins slowly but once the beans reach first crack, everything speeds up, and whether using the oven, a popcorn popper, rotisserie, or home-roaster, burning beans creates big problems fast. They can light on fire, create so much smoke the house smells for days, and ruin roasters in a hurry. Since green coffee beans cost $5-$10 per pound, it’s a real waste when they burn.
Cooling the Fresh-Roasted Coffee Beans
When the beans are pulled out of the oven, they have to be immediately cooled. They’re so hot that they continue to roast until they cool down. The best method is to immediately pour them into a metal colander, exit the kitchen, and stir them with a wooden spoon while they cool. The colander itself will take on the heat, so wearing a glove on that hand is a good idea.
The colander can be set in a 5-gallon bucket with an exhaust hole cut in the bottom attached to a shop vac. This takes some of the manual labor out of the process, but the concept is the same – keep cool air running through the beans.
The cooling process takes up to five minutes. When the beans are easily touchable, they’re cool enough that the roast is over. This is why you pull the roasting beans out of the oven slightly before they’re the desired color.
Coffee beans need to settle for several hours before brewing and most roasters need some time to cool between roasts. Taking care of the equipment and and taking notes helps to keep the finished product tasting as expected.
Enjoy the coffee.