This is a step-by-step guide to roasting green coffee with a popcorn popper. Read all of this before starting out.
Read This First: Roasting coffee uses very hot temperatures and can be dangerous. Always roast coffee outdoors away from combustible materials and keep a fire extinguisher nearby. Never leave roasting or hot coffee beans unattended as they could start a fire.
Additionally, popcorn poppers are not intended to roast coffee. Choosing to use a popcorn popper to roast coffee, including any appliance you may have purchased directly from us, is done at your own risk and you assume all liability if you decide to do so. The information provided below is an amalgamation of information widely available from many sources and provided here for convenience only, not as any recommendation for you to roast coffee in a home popcorn popper.
The Utter Basics
Without getting too much into the science of roasting (you can learn more HERE), roasting coffee with hot air – called a "fluid bed" – is a long standing practice. Simply speaking, the term is derived from the idea that a forced stream of hot air is used to both heat and stir the beans during a roast – exactly like an air popper makes popcorn.
With that said, this is a basic breakdown of what happens during a roast:
Green coffee has moisture trapped inside it. When you heat up coffee beans, this moisture eventually converts into gas. As this happens the coffee will begin to change color, and you will notice a few different smells, colors and even sounds. Once the moisture turns into gas, it will want to escape. To escape, it cracks open the outside shell of the bean, in an exciting, aromatic chemical reaction. This escaping gas will have an audible sound, known as “First Crack.” After First Crack is complete, your coffee will continue to roast (at a much faster rate) until the non soluble compounds expand and initiate their own escape, resulting in what is called (you guessed it), “Second Crack.”
Sometime after the beginning of First Crack and shortly after Second Crack is the range coffee is palatable and appropriate for brewing. But the range of flavors is dramatically different based on when you terminate your roast. Too early, your coffee will likely be acrid and sour; too late, your coffee will taste burnt. In either case, you can end up with something undrinkable.
If this is confusing, I promise it will make more sense after you roast and brew a few batches.
The biggest thing with roasting in a popcorn popper is that everything happens really fast. So do your best to prep everything before you get going. You’ll be running around like crazy if you don’t. Below is a bulleted list of what you’ll need – more detailed explanations and functions of each tool can be found at the bottom of this article.
- Fire Extinguisher
- Metal colander/strainer
See below for detailed descriptions of the above items
First things first. Get your popper located in a safe and convenient place outside and plug it in. Once you eventually get roasting, the chaff (the papery outer skin) from the beans will start flying out so pick somewhere outdoors. (Though a water bowl placed under the mouth of the popper does a good job at catching a majority of the chaff).
Gather all your other materials and tools outlined above.
When everything is ready, turn your popper on. We do not recommend preheating your popper before dropping your beans, as it gives the beans a few more precious moments to come up to temperature. We also recommend letting your popper cool down if you are doing multiple roasts in succession.
With the machine whirring, drop your coffee and immediately start your timer. Gently stir the green beans until the machine starts doing this by itself (after 15-30 seconds the beans will begin to shed moisture and weight and flow without stirring). If you’re doing more than 80g, you may need to stir throughout the roast – that’s fine.
At about the one minute mark you’ll begin to notice some visible changes in the color of the beans. What was previously green is now beginning to show signs of YELLOWING. At the same time you will begin to see some of the chaff begin to fly about. You can stir the beans during this period to encourage the chaff to fly out, and might use a small water bowl under the popper opening to collect it.
This is where things really get going.
At about 1 minute and 15 seconds, the beans will appear darker yet and you’ll notice a change about every 15 seconds. Check HERE if you want to understand the various phases of bean change.
More change is coming.
At about 2 minutes in, you’ll hear the beginning signs of FIRST CRACK. Note that first crack refers to a particular stage of roasting defined by a symphony of cracking, not one or two isolated pops. Timing of first crack changes based on bean type, processing techniques, and other factors, but in our experience with an air popper, this usually happens around two minutes and ends around three minutes. Just know that if yours starts later, not to worry. You will know First Crack is over by a trailing off of the popping frequency toward relative silence.
From here, your coffee and the sugars inside will really accelerate and every small increment of time/heat will affect the color and flavor of your coffee – Second Crack will not be too far off. Deciding when to stop your roast is a matter of personal preference and style. We recommend aiming for a color that approximates the color of coffee you normally purchase. Or, stop your roast right after the end of First Crack. Either way, you’ll need to brew the coffee to evaluate what range you prefer. We urge you to be extremely careful if you are roasting coffee to a dark color or into Second Crack as the oils gathering on the coffee bean surface can become combustible. Again, fire extinguisher nearby!
After a couple batches and brews you’ll get an idea of where you like your coffee. For us, we usually pull quickly after (or sometimes even during) first crack. But know that this roast will yield a brighter cup with more acid and nuance. If you are roasting for espresso or prefer a darker coffee, consider going a bit longer toward or just at the beginning of Second Crack.
Whatever you decide, when you’ve reached the color you’re aiming for, turn off the popper and immediately pour your coffee into your metal cooling tray/colander and turn off your timer, noting your discharge time.
Cooling and Resting
Cool your coffee by continually stirring the beans in the colander until they are cool to the touch (about five minutes) and then let it rest in a tray or on a plate for a few hours. Roasted coffee continues to develop (and brews differently) as it sits and releases CO2 gas. If you brew it right away, you won’t get the same profile as you will if you wait a day or two.
But, what the heck, if you want to give it a brew, go for it, without shame!
After a few hours, store it in something airtight like a ziplock bag. Note that for a day or two your coffee will continue to expel CO2 gas, puffing up the bag like a balloon. This is the sign of fresh roasted coffee!
And that’s it. Drink and repeat. And don’t forget to take notes on your roast techniques and the flavors of your coffee that you discover from changes you make. Use your notes as an invaluable guide to refer back to when roasting in the future.
If you have any questions, check out our LEARN PAGE where we provide a deeper dive into the various aspects of coffee roasting. Or, check out our 2 Minute Tips that provide a brief synopsis on all things coffee.
Important / Helpful Equipment
Don’t skip this. While no one ever expects to have a fire, that’s not an excuse to not prepare for one when you’re playing with hot things.
A scale is an important, but not a totally necessary piece of equipment to have. We usually do around 80 grams per roast, and then weigh it again when we’re done to calculate moisture loss (another variable worth tracking). If you don’t have a digital scale, 80 grams is about one cup (though different beans will have different density).
It’s important to note that you can roast more than 80g at a time, but the more you do, the more you will need to stir the beans. We’ve found that 80g is good for minimal stirring, and 115g is about the max you can do – stirring constantly throughout the roast.
A wooden spoon about 12 inches long or so works really well for stirring your beans while they are inside the popper. It’s critical to stir your beans right after dropping them inside, to give them a push start until the machine starts doing the work for you.
You can also use the stirrer during the roast to slow the swirl and check on your beans and examine their color, or mix them around to ensure a more even roast, and an ideal tool to agitate the beans while cooling.
The base of the popper tends to get quite hot during a roast, so we recommend a potholder or oven mitt to protect your hand when moving your popper, especially when dumping your beans into your colander or cooling device after you’ve terminated your roast.
We strongly urge you to use a notebook to log notes about your roasts. The more comfortable you get with roasting, the easier it will be to take notes while you’re doing it. The more variables you can identify, the more actively involved you will be in the process. As mentioned, your notes and the discipline to think about roasting details will accelerate your knowledge and understanding, leading to better coffee for you and your friends.
A timer is critical for keeping a useful roast log and replicating roasts. Start it when you drop the beans (the “charge”), keep track of when First Crack starts and ends, and also discharge time. The more experience you gain, the more you will be able to identify the different stages and their respective times. Either a portable oven timer or a phone stopwatch will work fine.
It’s critical that you cool your coffee immediately after you pull it from the roaster. Coffee will keep developing while it is still hot, so try to cool it as fast as you can. As mentioned, a metal colander and wooden spoon is the easiest method we’ve found. If you have two colanders/strainers, you can pass the coffee from one to the other. Anything to get the beans in contact with ambient air. For the real home-hacks, you can probably rig something up with a portable fan but we’ll let you take the lead on that one.
Water Bowl for Mess Control (optional):
If you’re okay with chaff all over your back yard or balcony, feel free to skip over this tip. If not, we recommend filling up a bowl or pot with water and placing it underneath the mouth of the popper. If you roast with the plastic popper lid on, the chaff will be redirected out of your popper, and stick in your bowl.