I've been asked to elaborate a little bit about this air roasting thing by a number of folks in recent days, and how it differs from the way most roasters roast their coffee. The bottom line is that fluid bed air roasting is a cleaner method of roasting coffee! While I won't say that it's bad to use a fueled (gas/propane) drum roaster because it has some advantages, I will say it's simply not as clean! One of the problems is that when you burn a fuel you get byproducts from not only the combustion gases but also from the delivery source such as the tanks and pipes. Unless you have a filtering system you could be getting all kinds of particulate matter and contaminates from the delivery system alone.
Excess fumes from any heating source can alter the aroma and flavor of any food that is cooked/roasted with it. Now, just think for a moment about the barbecue... not a bad thought! One of the big appealing things about barbecuing is that you get the flavor and aroma from the coals and or wood that you're cooking with. Right?! Well, when you roast coffee with a fuel the same thing happens. Now, I know for the most part you're not thinking that you're tasting anything "extra" on your coffee however, you have no frame of reference to base this on and most of the off flavors have been allowed to off gas from the coffee by the time it is sold to you so, unless you taste side by side you may not know (unless you taste everything like I do). When you take and compare beans to beans there is a notable taste difference between the air roasted and the gas roasted coffees. Not because the guy using the air roasting method is a better roaster! On the contrary. It takes a lot of years and hard work to roast a really good coffee (although it's not as hard as it's made out to be in the industry). It's that the air roasted coffee is cleaner and less polluted than the gas roasted coffee. Now, while it's not as extreme as the difference between a grilled steak from the BBQ and one from a frying pan there is a difference!
"So, I would have thought the more flavor the better!" This is very true when talking steaks but coffee is another fish altogether! Coffee has such an amazingly diverse flavor profile from each and every region around the world that it's grown in and based on the variety of blends and roast levels one might create with them. It's just a shame to mess with nature in this way. Kind of like using a fine single malt for your mixed drinks! While we all like having a good smokey meal off the barbecue with the enhancements of the fuels used to cook it with; we would never wax eloquent about the gas flavors or the particulate matter imparted to the coffee by the utility company's pipes!
We can argue about the need to let the coffee "rest" after roasting but... if we want to have a discussion about how cleanly roasted the coffee is there is no argument. If all you are doing is heating the air that you then are passing through the beans to roast them and if that air is heated with a non-fuel heat source, you are getting a cleaner and perhaps healthier coffee. And you're not using excess fuel just to have your morning Joe! And from that stand point if your goal is to conserve energy and pollute less then this is even better! Yes, it uses electricity! But, the system we use is very efficient, not really using much more than a regular roaster would use to operate on. The big difference is that we don't need gas on top of electricity to achieve the same (and maybe better) results!