Can we roast green coffee in a hot-air fryer, will it taste any good? What is a hot-air fryer anyway? 
It’s one of these new kitchen devices that promise to fry anything (french fries, chicken wings, etc) and bake (bread, cake) with hot air and with little or no fat at all. These fryers have now been on the market for a couple of years and are becoming increasingly popular and more affordable. In essence, these are small convection ovens, ideal for a single household or a household of not more than three persons. The maximum temperature this machine can supply is 200°C (392°F). I have measured the temperature with an electronic thermometer which unfortunately could only read up to 200°C. After three minutes of pre-heating, the thermometer said “out of range”, meaning the temperature was more than 200°C, I would guess close to 210-220°C.
Is this temperature enough to roast coffee? Good coffee? I experimented with several different vintages of coffee, varied the time (but not the temperature). The best results were achieved with an Arabica from North Sumatra which I had dried at 40% ambient humidity for several months. The process was ridiculously easy: Preheat (3 minutes), then roast for 9-10 minutes, stir the beans a few times during this period. First crack is heard after about seven minutes. When done, immediately, put the beans on a cool surface (I am using a fresh kitchen towel). Done. The roast (see picture on the right) is what would be best described a “City Roast”, a medium degree of roasting. After a few days of letting the coffee rest in a jar, I tried: Perfect, for my taste! OK, other people may have different expectations, but as regards me, I as quite pleased with the result.
There are drawbacks: medium “City Roast” is the maximum; due to the temperature limitations of the fryer. Roasting longer, say, 15 minutes does not make the beans any darker. Also, another test with a different vintage of Robusta beans from West Java just did not make it: The beans remained too pale which later yielded a coffee that was just acceptable but far from perfect. I suppose, – as always – there needs to be some testing with every new batch of green coffee.
Conclusion: Roasting coffee with a hot-air fryer is surprisingly easy, works fine and is a simple process that can be done at home. Taking into account that there are computer-controlled roasting machines on the market which cost more than US$ 1,000.- (I wonder if their output tastes so much better?), I am quite delighted with the process and the result.