Earlier this year, Cook’s Illustrated ran a little blurb about using a hot-air popcorn popper to roast coffee. (The March 2013 article is online, but behind a pay wall.) If you’ve followed my blog, you might suspect that this is something that would intrigue me. It involves coffee, and it’s quirky (like making my own marmalade or maple syrup). But until recently, I’ve had two problems: no green coffee and no hot-air popper. Show stoppers.

In the last month, I’ve taken care of both of those problems…

Green coffeeIt turns out that Laurelville’s new director is also a home-roasting coffee aficionado. When he arrived in May, he pointed me to Theta Ridge, a supplier of direct and fair-trade coffee (and gave me some green coffee to experiment on). And when he placed his most recent order, I asked him to get me two pounds of beans, as well. The beans arrived yesterday. Problem #1 solved!

(But wait – it gets better. The coffee I ordered is of Mennonite origin! It comes from Strong Tower Children’s Home. The home is a ministry of Conservative Mennonite churches in El Salvador, and their coffee supports their work.)

West Bend hot-air popperAs for the second problem, the solution was even easier. Laurelville had an old, unused popper in the attic of the Dining Hall. And the nice thing about old poppers is that they lack some of the safety features of newer poppers. (“And why is that a good thing?” you ask. Thanks for asking. Let me tell you…) This particular popper doesn’t shut down the heating element when it gets above a certain temperature. This is important if you like a dark-roasted coffee. Just make sure that you don’t melt the sides of your popper…

And with those problems out of the way, the fun began. I had run some (mostly unsuccessful) trials earlier, but I got serious yesterday…

Massing the coffeeRoasting with a popper is definitely a small-scale operation. Given the volume of the popper, I use about a quarter cup of coffee (about 46 grams, which is what I used in the first batch) at a time. (And yes – I tared the scale with the measuring cup in place. I’m a scientist, after all.)

After getting the popper warmed up, I dumped in the coffee. At first, I tried to roast with the popper uncovered, but that took longer than I wanted. (If the roasting process goes on for too long, the beans end up baking.*) So I tried covering the opening with foil, but then the process went too quickly. In the end, having the popper half-covered worked well.

Roasting the beans* A couple of weeks ago, Ordinary Spouse described the flavor of some of my baked coffee as ‘rustic’. This time, I wanted something better than rustic.

After about a minute (with the popper half covered), the chaff was flying off the beans, which were turning yellow. And a minute or so later, the beans reached ‘first crack’. (This is a point in the roasting where one can hear a sharp snapping sound as steam and carbon dioxide are liberated from the bean.) If you like a light roast, you can stop after first crack. I kept roasting.


At about five minutes, the beans were getting dark – roughly a medium roast by my standards. Soon thereafter, the ‘second crack’ began. (This sounds a bit like a bowl of rice krispies – not as loud as first crack, but maybe more exciting.) During second crack, little bits of the outside are getting flung off the beans. This is a dark roast. In my roasting yesterday, I was still experimenting with when to stop the process. Sometime during second crack, I dumped the coffee onto a cooling sheet.

Roasted coffee

(If you look closely at the coffee above, you can tell that it comes from two different batches. The coffee on the right is a medium-dark roast that I stopped near the beginning of second crack. The coffee on the left is darker. I pushed it most of the way through second crack.)

At first, I wasn’t real impressed with the coffee smell. It was just a smoky, roasting smell. But as the coffee cooled, it started to smell really nice. Things were looking good, but the tasting was yet to come. Finished massBy the way – the roasting process drove off roughly 7 grams of water or other volatile compounds (15% of the pre-roast mass).

All told, I roasted a cup and a half of green coffee yesterday. Interestingly, the final volume was double the beginning volume – three cups total. And I roasted more today.

This morning (after letting the coffee mature for about twelve hours, which is supposedly ideal), I made a cup for Ordinary Spouse, who is the official judge of my roasting skills. She has declared it to be a success!

I’m having way too much fun.


(A lot of my information has come from Sweet Maria’s, which is a great source of information for home roasters. If you’re interested in doing your own roasting, I recommend that you start your learning there.)