This blog post will discuss the Whirley Pop method of home roasting. All you need is a stove top and a hand-crank popcorn popper. To improve the process, you'll want a thermometer (that reads up to 400 degrees Fahrenheit), a timing device, a vent fan, and a couple of colanders (for cooling the beans).
Home roasting is an activity that's growing in popularity and there's numerous methods for doing it. At the most basic level, you could throw some beans on a cast iron skillet and move them around with a wooden spoon until their roasted. The most popular method seems to be using a air popcorn popper and you can find ample information on that with a simple web search. Stove top roasting is how I got my start, so that's what I'll discuss today. Its been over two years since I last roasted with my Whirley Pop and when I pulled it out this morning to give it a try again I felt both apprehensive and excited. Once I got going, the excitement took over as I remembered the thrill and intimacy of roasting a small batch of coffee on my own stove. Ultimately, roasting coffee is pretty simple and you too could experience the joy of brewing a cup of coffee that you roasted the night before.
Now to the fun part. I measured out 8 ounces of green coffee (if you don't have a scale, use a volume of between 1.3 and 1.5 cups). I opened a few windows (ideally you should have a good vent fan), set the Whirley Pop with thermometer on the stove and cranked it on to level six (you may need to tinker with you heat levels, especially if you have a gas stove). My goal was to roast the coffee in about 12 minutes. If you roast too fast you will lose some control over the process and flavors might not develop well enough, too slow and you will waste precious minutes of your life, plus stalling the roast can lead to imperfect flavor development. But don't fret too much about that; any coffee that is fresh will likely be better than most of what you buy off the shelf at the grocery store.
I watched the temperature climb and when it hit 100 degrees I poured in my beans, started my timer and cranked away. Now, you must crank without ceasing until the roast is over or else you will scorch and burn the beans. My strategy is to watch the timer and every thirty seconds I lift the Whirley Pop and give it a shake (see video below) in order to keep the beans thoroughly mixed around; I believe this helps contribute to a more even roast.
As I cranked away, the minutes passed and the temperature continued to climb. My goal was to get it to 300 degrees and then have it stabilize between 300 and 350. After about seven and a half minutes it got up to 300 and I turned to stove down from level six to five. The temperature continued to slowly climb, which was what I wanted.
At eight and half minutes I heard the first cracking sound. This is important because I am gauging the roast level primarily by sound (with the temperature reading as a guide). While you can open the lid to look at the bean color, I prefer not to because it lets a lot of smoke and heat out, and its rather hard to see the beans clearly through the smoke anyway. When roasting, you need to know about first crack and second crack. First crack occurs when the beans have reached an internal temperature of around 390 degrees (remember that our thermometer reading will be lower than that since the surface of the popper will be hotter than the air temperature above the surface). As the bean temperature rises the sound of popping/cracking beans will accelerate and then taper off as the roast progresses. These are the sounds of chemical transformations happening within the bean and it's the critical period when your green coffee seed is being converted into a delicious and aromatic coffee bean. After first crack is complete you can cut of the roast at anytime. This would be a light roast. You may want to use a flashlight to check on the color and keep roasting until you are satisfied (as I said before, my preference is to not open the lid). For a darker roast, you will keep going until you hear "second crack." This occurs at a bean temperature of around 445 degrees and will sound more like a soft, rapid crackling as opposed to a loud popping. As second crack gets going you are entering the stages of a "Full City" or "Vienna" roast. Smoke production will start to increase and if you let it go too much longer (entering the realm of a French Roast), the smoke will really go crazy and probably overcome the limits of your vent fan.
Back to my roast. As first crack accelerated and then tapered off, the temperature reading stabilized at around 340. I didn't want the temp to start reducing, since the beans were going to require more heat input in order to continue their progression, so I turn the knob back up to level six.
I kept cranking away and at around 12 minutes I heard the first signs of second crack. At 12:30 "second crack" was pretty clearly underway, smoke was started to emerge a little more rapidly, and I was satisfied. I turned of the heat, grabbed my colander and Whirley Pop and rushed outside. Once you dump the beans into the colander, the smoke will come rushing out, so I don't recommend doing that inside. Its a good idea to have a second colander or bowl ready so that you can pour the beans back and forth in an effort to cool them down as rapidly as possible. There will also be a coffee chaff present that you will want to separate from the beans. When you pour the beans between colanders, simply blow on them to release the chaff. Don't worry about getting it all out; it won't hurt anything.
My eight ounces of green coffee produced 6.7 ounces of roasted coffee (coffee loses weight but gains volume from roasting). I'm rather proud of the results. The coffee looks and smells amazing and I can't wait to brew it tomorrow morning.
If you've followed these steps and now have the freshest coffee you've ever seen, you need to know that your beans will be emitting CO2 for the next few days. If you seal them tight in a mason jar overnight, you might get a bit of a scare when you open them in the morning and the lid comes flying at you. My general rule is to keep the lid loose for a day. After that you still need to make sure you release the pressure periodically. Off-gassing will slowly taper down but won't stop completely for about a week.
The video below shows two minutes of the roasting process as it went into first crack. Unfortunately, you can't hear the cracking very well over the noise of the cranking.