Saturday, September 21, 2013
I have had three small home coffee roasting machines. The first was a Cuisinart "robo cafe", which Cusinart U.S. claims never existed (it appears to have been marketed primarily in Japan, but I got one from a nice kitchen store in Boulder). It was designed to roast, grind, and brew, which is cute but basically a bad idea. My second was an air roaster from Hearthware, a Korean company, and it was excellent for the three or four years it lasted. Then I had the next model of Hearthware, which was nearly as good. And then Hearthware pulled back from the home coffee roasting market, stopped supporting their products well, and so ceased to be a good option. What to do?
The Hearthware units operated on the same principle as hot air popcorn poppers. They are also known as "fluid bed" roasters, because the hot air (the fluid) lifts and stirs the beans as it roasts them. This is the same principle used by large commercial roasters, and it works well. There are other fluid bed roasters on the market, but they are not as well made as the original Hearthware units. One can also hack some popcorn poppers to convert them to coffee roasters, but I've never felt comfortable doing that.
Small commercial roasters (like your local coffee shop, if it roasts its own) use drum roasters. These turn the beans in a metal drum, which transmits heat to the beans. There are also home roasters that use this approach. Air roasters cost around $100-$150 dollars; drum roasters for home use are in the $350-$700 range. I seriously considered this option, but it's a non-trivial investment, and in addition the drum roasters present a larger challenge in smoke management than the air roasters.
There is a third, relatively cheap option: Put the coffee beans in a metal dish (typically a dog food bowl), and apply heat with a heat gun, like those used to peel paint. Like air roasters, this method uses air to deliver heat to the beans, but the beans do not float on a fluid bed of hot air. Rather, they slide around a bit in the dog bowl, which gets pretty hot and possibly also transfers a bit of heat through conduction, like a drum roaster. (I am a little skeptical that this contributes much to the roasting.) There are pretty good instructions for getting started online. It seemed like a good idea to at least try this cheap method before investing in a drum roaster.
So ... after much delay, we bought a heat gun and gave it a try. First I tried roasting some older green coffee left over from when my last Hearthware died. It was pretty disappointing. Then we bought some fresh green coffee from Sweet Marias, my supplier of choice, and it was better. And a little better. And, eventually, really good.
Impressions so far: Dog bowl roasting is a lot more challenging than using an air roaster. It takes a good deal of trial and error to find the right amount of green coffee to roast and to find and technique to achieve even roasting and the desired roast profile. Currently I use 100 grams of green coffee (because that amount seems to stir well in the hot air, while also retaining heat well enough), and I use the heat gun on low and very close to the beans for several minutes to reach first crack, then switch to high heat from a greater distance to rapidly take it from first to the desired level of roast (usually a little into second crack). Results still vary a lot, after a month or so of roasting roughly every third day. Occasionally it is very good indeed.
Today we took pictures at 30 second intervals during a roast, to illustrate how the color of the beans changes during the roast, as well as to show the basic setup.