A Roaster is a simple machine. It is designed to use heat and air (the two manipulatable elements of a roaster) to gradually increase the temperature of something as dry as a field of grass to very high temperatures as the roaster coaxes out the delicate flavours of the green coffee...
There are essentially two types of Roasters:
1. A Drum Roaster.
2. A Fluidized Bed Roaster, or "Air Roaster".
The fluidized bed roaster is the newer of the two technologies. It is designed to have coffee float on a “bed” of hot air. This method roasts coffee about 50% faster than a Drum Roaster. But that is not necessarily a good thing.
I have heard more than one roaster who chose a fluidized bed over a drum roaster, say that their main motivation for doing so is that “a fluidized bed roaster is gentler on the beans because a drum roaster scorches the coffee when it comes in contact with the hot surface of the drum”.
This popular opinion is less than half the story:
1. Scorching (or “tipping” as it is known to roasters) in a drum roaster is the affect of ineffective training, or a lack of knowledge on the part of the Roaster, and is easily corrected if the roaster has the skill to evaluate the density and moisture content of the bean prior to roasting. Hard beans (those grown at high altitudes and of incredibly high quality) are almost impossible to scorch and in fact require a very high “charge” temperature (when the beans are dropped from the hopper into the roasting drum).
Softer beans, (those grown in countries that lack high altitude growing regions, yet provide exceptional coffees like Brazil or Indonesia for example) will produce “SS” or Strictly Soft beans. These beans need to be handled with care, lowering the drop temperature and taking care to not let the roasting process develop too quickly by keeping the heat low without unnecessarily stalling the process.
In short, “tipping” is the result of a lack of knowledge and skill of the person (roaster), not the machine (drum roaster).
2. Drum Roasters that are produced in countries that tend towards copying existing roasters without fully understanding the reason for material choices, (Turkish Roasters for example have this reputation and tend to be more prevalent in developing countries), lean towards the use of Stainless Steel roasting drums. This is a major problem because Stainless Steel has no ability to disseminate heat, meaning the drum has definite and intense hot-spots which will scorch and tip coffee. Proper research and purchasing only the best equipment money can buy will further prevent scorching and tipping.
3. Probably the worst thing about air roasters, is the lack of control that a fluidized bed roaster provides.
In a Drum Roaster, the Roast Master controls the ambient and bean temperatures as well as the convective (air-induced heat) by controlling how much air is flowing through the drum. The more air, the quicker the temperature increases and the faster the beans roast.
Understanding that simply principle makes it easy to understand how a fluidized bed roaster consistently roasts coffee in almost half the time of a drum roaster. Why is that a bad thing, you ask?
Any Roast Master will tell you that the importance of being able to intricately control the temperature of the roast as the coffee approaches the first crack and between “Cracks”, as well as to be able to slow it down or speed it up (along with knowing when to do one as opposed to the other) cannot be overemphasized. Yet, this is not possible on a fluidized bed roaster. The only controlling factors on a fluidized bed roaster are: charge temperature, time, and drop temperature, rendering this a roasting method more suitable for “Quantity” roasting as opposed to “Quality” roasting.
Drum Roasters on the other hand place complete control in the hands of the Roast Master. Being able to speed up or slow down a roast at a moments notice, and being able to control the development of all the flavours in the beans as they are roasted with care and precision. While yes, it does take more time and effort to roast using a drum roaster, the quality of the final product cannot be disputed, and this is the reason that FIX! Coffee only uses Infra-Red Drum Roasters.