Google "fluid bed vs. drum roasters" and you'll find a thousand opinions on which is best. The truth is I've had great coffee from both systems. I do prefer fluid bed and here are some reasons why.
1. The longer and hotter the beans are roasted, the more flavor escapes. A commercial drum roaster can take 15, 20 or more minutes to roast a batch of green beans. The same batch size of green beans can be roasted in 6 to 8 minutes in a commercial air roaster. The longer the beans are subjected to roasting temperatures, the more flavors and aromas volatilize away.
2. Air Roasters provide consistent temperatures to all of the beans in a batch. Fluid bed air roasters are called “fluid” because of the fluidity of movement the beans are allowed, not because water is involved. No water soaking is involved in any air roaster we have heard of. We do recommend spraying clean filtered water on the beans in the cooling pot after the roast to bring the bean temperature down more quickly. The water turns to steam immediately and is evacuated through the exhaust system. Hot air coffee roasters are a lot like hot air popcorn poppers. The beans float on a bed of air in the roasting chamber, allowing all of the beans to be heated to exactly the same temperature at exactly the same time. Degree of temperature directly correlates to degree of roast. In drum roasters, the beans sit in the drum and are stirred with a mechanical arm. Depending on whether they are directly on the drum surface or in the middle or top of the batch of beans, the coffee beans reach the optimum temperature and ultimately the “second crack” at different times, resulting in an inconsistent roast. Roasting can be uneven and some beans that remain in direct contact with the cylinder too long are scorched. This is a much less controlled method.
3. Drum Roasters trap and burn coffee bean chaff. In a drum roaster, much of the chaff that comes off of the roasting coffee beans remains in with the beans throughout the roast. The chaff burns and smokes, causing a burnt flavor, especially in dark roasting. In an air roaster, the chaff rises into the cyclone and is deposited into the chaff collector as it comes off of the beans. It does not burn and damage the flavor.
4. Operating an air roaster takes far less training than drum roasters. Drum roasters include a lot of complicated controls that the vast majority of roasters do not use. In all my travels I've yet to see a roaster who used all the fancy controls provided with the roaster. Walking up to a drum roaster with controls that resemble an aircraft cockpit does not instill confidence.
5. Fluid bed roasters are so fast you can custom roast one pound orders back to back while customers wait. This is something no drum roaster can do! These are the main reasons one would choose an air roaster over a drum roaster. The drum vs. air debate has been going on for a long time. Most consumers do not know the difference. They just know what they like and as the average person’s palette is becoming more educated, they are turning away from the traditional burnt taste of drum roasting. There is one thing fluid bed and drum roasters do agree on. Fresh roasted coffee from either system is vastly better than the stale coffee consumers buy at the supermarket.