This post is newly revised and updated after previous publication on my Tumblr in 2013.
As some readers may be aware, I roast coffee at home, and have done so for a number of years. For the first two and half years, I roasted with a hot air popcorn popper (as I discuss in the above link). But when my popcorn popper died, and the replacement died immediately too, I decided, after consultation with my friend Brian Gumm, to start roasting with a heat gun instead. (Brian has since graduated to a professional roaster and roasting business, and I’m thrilled for him. Try his coffee!)
Heat gun roasting, however, is not Sweet Maria’s-supported, so whereas you can learn all you need to know about roasting with a popper on a single website in a short amount of time, it’s much harder to educate yourself about heat gun roasting. So I’m putting up this post to aggregate a few of the best resources I found and add a few of my notes on how to roast successfully. I’ve done about a dozen roasts now with the heat gun now, so I feel like I have the basics down, but these should still be taken as initial notes–and I’ll likely update this post later.
Why you should roast with a heat gun
A popcorn popper is still the most sensible option if you’re just getting started with home coffee roasting, because it’s hard to screw up and a great way to learn the ropes. However, a heat gun offers one major advantage–the ability to roast more than about a half-cup of beans–without being significantly more complicated or more expensive. You could probably roast a pound at a time with a heat gun, and although you should know a little bit more about the changes the beans go through as they roast, it’s not that much more than you need to know for popper roasting. An added benefit, once you get familiar with the process, is that you have a lot more control over the roast and the ability to tweak it for better flavor. But the bottom line is that whereas with a popper I was roasting about every other day, with the heat gun I roast about every 4-5 days.
The most comprehensive guide, via Brian Gumm and mercifully preserved by the Internet Archive.
The most useful video, involving roasting in a metal bowl rather than a bread machine.
Scott Rao’s book on coffee roasting is a great resource if you feel like dropping the money on it.
You can also find tips on listserv archives and forums, but that’s a lot of work and I don’t have readily-available links to anything crucial.
These are going to reference that first video link, because that’s the closest to how I do it.
I roast in a metal bowl rather than a bread machine. It requires a little more physical effort, but it’s not bad.
I skip the trick from the video where the guy puts the smaller bowl inside–I found myself jostling the smaller bowl no matter how hard I tried to avoid it, with the result that beans would get stuck under the little bowl and fail to roast.
Instead, I have found it to be very important to preheat the bowl for a couple of minutes before I put the beans in. This reduces my time to first crack from around 10 minutes to around 6 or 7. This is not only efficient, but if you’re aiming for lighter roasts (as I am), you’ll get better flavor from a faster roast development, and make sure to avoid undesirable “baked” notes.
I avoid stirring the coffee with the heat gun (as the guy in the video does), because I have had occasions where a bean will get stuck in the gun and burn to a cinder. YMMV depending on your heat gun, though. I do hold the gun as close as I can to the beans until I get to first crack, and keep my heat gun on its hottest setting (I bought the cheapest, smallest one from Home Depot, and it has two settings) for the whole roast.
Once first crack starts, however, I’ve found it to be necessary to hold the gun farther from the beans, or you can end up crashing through into second crack way too fast. That’s obviously a problem if you want to keep the roast light, but even if you want it darker it will taste better if there’s about 2-3 minutes between first and second crack.
For cooling, I use a pizza pan rather than a colander–because I had it and wasn’t using it for anything else, and because it works. I have also used a fan, a water sprayer, and a colander. I don’t think any of these tools or methods is vastly superior to another.
As my previous post on this states, my priority in coffee roasting is to make it simple for myself. I’m not a hard-core roasting expert or a gadget-making tinkerer, although I do obsessively refine any process like this that I perform regularly. This is a little more fussy than popper roasting, but it still works for me during a phase of life with two small children in the house.
I’d love to hear other tips, see other resources, or answer questions, so get in touch if you have feedback.
I’ve been roasting long enough now to offer a few more tips.
If you are shopping for a heat gun, I would recommend getting one with no less wattage than 1200. I have the standard Wagner they sell at Home Depot, and I have sometimes found myself wishing I could get more heat out of it, so if it’s in your budget, I would spring for something bigger. I’ve found that roasting a whole pound does not work well with my current setup, and ambient temperatures below about 40 degrees make roasting nearly impossible.
After I mastered the basic technique, I’ve begun to explore using the manual control afforded by the heat gun method to achieve certain roast profiles. I’m not using a thermometer (yet), so this is purely based on observation. Right now I’m working on accomplishing the roast curve outlined by Scott Rao, in which the coffee undergoes an initial spike of heat, then a drop followed by a curve up to first crack, then completing the roast within about 25-30% of the total roast time. To achieve that technique, I’m trying a couple of things: in the first minute or so of the roast, I stir the coffee only minimally, to produce that heat spike. Then when I get to first crack, I keep the heat on high (the gun as close as possible to the beans) for about the first minute of the roast, then back off by about an inch until the completion of the roast.
Update January 2018:
Note on heat gun purchases: save your receipt and cash in the warranty if it dies on you, as it well may. I have had two die within a year of purchase, and was able to get one replaced on warranty.
Pretty soon, I intend to move beyond the heat gun method and set up this roaster that my friend Daniel Grey put me onto. It costs about $70 to set up and loses you some control, but it’s hands-free and lets you roast more than the heat gun. Further bulletins as events warrant.