There are many ways to roast coffee at home. One of the most basic and least expensive methods is the oven. Yes, you can easily roast your own coffee at home using an oven. It doesn’t make the brightest, most flavorful coffee, but it works. If you’ve never home roasted coffee before, you may be impressed with the outcome.
What supplies will you need?
- A decent oven capable of reaching higher temperatures (more details below).
- A baking tray or cookie sheet. The best kind will have small perforations, like those used for cooking pizza.
- Timer or stopwatch.
- Oven mitt. Due the the high temperatures, an Ove Glove is ideal.
- Wooden spatula.
- Metal colander(s) for cooling.
- Water bottle with mist spray – if you live in a hot climate
- Green coffee beans. Between 1/3 and 1/2 pound works best.
More on the Oven
All ovens are different. What the temperature says and what it really is can vary. An ideal oven will be able to reach 470F – 500F. It will also have a window for clear visibility during the roasting process. Test your oven to see if it has a working light. If it doesn’t, you should have a flashlight handy. You’ll need that to perform visual inspections during the roast. The amount of time it takes to roast can vary from oven to oven and bean to bean. The last thing an ideal oven will have is excellent ventilation as roasting coffee produces smoke.
Preparing the Roast
While you prepare the coffee roast, turn on the oven and set it a high temperature. I’d love to tell you exact temperature, but it will vary from oven to oven and gas to electric. Try 475F for gas and 500F for electric to start. I’ll discuss dialing in the tempreature later in the article.
For oven roasting, I like to use a perforated baking pan. Be careful not to use one where the holes are too large, as some of the beans will fall into the holes and then expand during roasting. Spread the green beans over the holes in the pan so that the beans are 1 bean deep and touching. Don’t stack the beans on top of each other.
Smooth green coffee beans over tray. Note that the tray in this photo is not ideal. The holes turned out to be too large.
In addition to preparing the tray, you’ll also want to be ready for the smoke that is produced during the roast process. The more coffee you roast and the darker the roast, the more it will smoke. Your oven ventilation may not be enough to keep your smoke detectors from going off. The last thing you want during your first oven roast is a panic attack. Open windows, turn on fans and if you can temporarily disable your kitchen smoke detector. Also alert others in the house on what you are doing.
The last step in preparation is coming up with an exit strategy. When the beans come out of the oven, they will be extremely hot and still have chaff on them. Chaff is a thin tissue-like skin that you’ll want to knock off the beans as much as possible before grinding. But the most important task post roasting is to cool the beans. Your goal is to get the beans down to room temperature as fast as possible to prevent the beans from continuing to roast. My advice is to create a path from the oven to outside or to a patio. This is where you will cool the beans and remove the chaff. More on that later.
Monitoring the Roast
Once you’ve got your tray of beans ready and you have both a ventilation and exit strategy in place, confirm that the oven has been pre-heated and then place the coffee tray into the oven. Start your timer. The coffee will go from green to yellow to light brown to a darker brown. Color is very important to monitoring the roast. You don’t want to burn the coffee.
Oven Roast Progression
Since not all ovens or baking trays are equal, some beans – especially those on the outside edges – may start roasting faster than others. In you see an unevenness in the roast, pull the coffee out and use your wooden spatula to stir the beans. Then quickly place the beans back into the oven. Ideally, this should be done no more than twice during a roast cycle, as each time you open the oven door, the temperature will drop. If your oven struggles to get high temperatures, you may be better off letting it go and then picking out the burnt beans later.
Coffee roast with uneven edges. The beans on the outside are roasting faster. If this happens, pull the roast, give a stir and return to the oven quickly.
Listening to the Roast
In addition to watching the color of the coffee beans change, you’ll also be listening. Coffee produces a first crack and if you roast long enough a second crack. The first crack is a popping sound. At first you’ll hear a few beans and then more. Then the cracks will fade and the coffee beans will be quiet for a few minutes. Then comes second crack, which is more of a crackle sound. Depending on how you like your coffee, you may decide to end your roast here. If you like darker roasts, let it go a little longer, but not too much.
Listen to the 2nd crack of a coffee roast.
The downside to roasting coffee in an oven is that you can’t quickly move the temperature up and down. A dedicated coffee roaster will usually start a lower temperature and then heat is increased gradually throughout the remainder of the roasting cycle. This allows the coffee to develop more complex flavors. You can’t really do that with an oven, which is why the roast temperature starts and ends high.
This means the roast will often be faster than other methods. If your oven is extremely responsive, you can start the roast at a lower temperature and then increase the temperature as the roast progresses. This is will enable a longer roast cycle to develop more flavors without burning the coffee.
Dialing in Your Oven Roasts
My roasts with an oven tend to be around 10 minutes. If you can get 15 minutes without burning that would be great. Anything shorter than 10 minutes and I’d advise dropping the temperature. Take notes on times, temperatures and of course taste. Also make sure you are using the same amount of green coffee each time. After a few roasts, you should start to get a feel for your oven.
Stopping the Roast and Cooling the Beans
Once the beans achieve your desired roast, stop the oven and remove the beans. Use a Ove Glove or a really good oven mitt. Also be prepared to be face to face with a cloud of smoke. Don’t panic. Take your coffee to where you plan on doing your cooling. I like going straight outdoors or to a patio, but it isn’t required.
Dump the beans from the baking tray into the metal colander. If you live in a very warm climate and there is no breeze, you may need to lightly spray mist water on the beans to cool them down. Don’t drench the beans, just lightly mist the cold water over them. It should evaporate immediately and cool the coffee beans in the process. If your squirt bottle can’t mist, don’t use it. Anything more than a mist will do more harm than good. Be sure to test the mist before using it. Some home roasters disagree with this method, but I’ve used it many times when I lived in Florida and Southern California. Another idea is to roast in the early morning when it is cooler.
I use a 2 metal colander technique for quickly cooling the coffee beans.
Once the beans are in the metal colander, shake them gently. I use two metal metal colanders and pass the beans back and forth. Doing this also knocks the chaff off the beans.
Oven Roasting Step-by-Step
- Preheat the oven to 475F – 500F or whatever temperature you’ve calculated works best for your oven.
- Spread the beans over the perforated baking pan so that they are no more than one bean deep. Make sure they are close together.
- Open windows, turn on vents, alert family members and possibly disable kitchen smoke detector.
- Set up cooling station with metal colander, preferably outdoors.
- (hot climates) Have spray bottle on mist ready to go. You just want a light mist. Test spray bottle before using.
- Place pan into oven once it is pre-heated.
- Monitor the roast for color, sound and roast evenness. The beans will take about 10-17 minutes to roast.
- If beans are roasting uneven, remove from oven, stir with wooden spatula and quickly return to oven.
- Once roasted, turn off oven, remove the pan and head to cooling station.
- Place the beans into the metal colander and begin (gently) shaking to cool and knock off chaff.
- (hot climates) Apply a light mist with your water bottle.
- Let house clear of smoke. Using a floor fan will accelerate this provess.
- Apologize to any firefighters that may have arrived to your home.
- Enable smoke detector and confirm oven has been turned off.
- Allow 24-48 hours for beans to de-gas before brewing.
How much you enjoy oven roasting coffee will really depend on your environment and how picky you are about your coffee flavors. Kenneth Davids, the author of Home Coffee Roasting: Romance & Revival, states that oven roasting isn’t best for very light or very dark roasts.
Ovens tend not roast the beans as evenly as other methods. When I roasted from a small apartment using an electric oven, my coffee tasted flat and my apartment was filled with smoke for 30 minutes. My cat was not amused. Then when I tried in a larger kitchen using a new gas oven, my results were much better. Will it work for you? Give it a try and find out.
In 2007, Michael moved to America's coffee capitol Seattle, Washington. He has visited close to two hundred different coffee places in Seattle, Portland and Vancouver and met many of the top roasters and baristas in the country. Since 2009, Michael has been the Organizer of the Coffee Club of Seattle, which is a Meetup group of over 600 coffee enthusiants. Besides the social aspect of the group, the Coffee Club of Seattle partners with local coffee professionals for educational events such as coffee cuppings, brewing demonstrations and roasting tours.
Unrelated to coffee, Michael has a personal blog at CriticalMAS.com which covers several topics including fitness, cooking and finance.