Coffee beans, how should one be roasted? Would it have to drum roasted in a fancy European nineteenth century machine, the way coffee beans were traditionally roasted? Or should they be roasted in speed in an air roaster? In the world of coffee this seems to be the most debated topic.
So what is the fuss about? So let’s look at each of them in detail: There are two methods of roasting coffee beans. The most common method is the drum roasting method. Nearly all commercial roasters are drum roasters. Conversely, most home roasters are Air Roaster or a Fluid Bed Roaster. A fluid bed roaster uses a stream of hot air to roast the coffee beans. The air is of sufficient force to cause the beans to circulate or to swirl which gives the beans the appearance of being a “fluid bed.”
Of course, it seems to be a hopeless discussion which one produces better coffee, since we are talking about a process where the final arbiter of the result is the tongue of an individual and we have not invented a tasto- meter to measure how much one likes the taste of something. Drum roasting has artistry on its side. It’s is like fine dining with the freshest ingredients, slow cooking the sauces and faithfully oiling ones cast iron skillet. The equipment is one that can belong to any museum. Commercial drum roasters are big, attractive, expensive, old-world-European-looking machines. So in essence it is a tradition roasting one of them.
Air roasting has less intrinsic charm, unless you are really into hair dryers. But the roast is easy to observe, the process is “clean” because there is no effluence from atmospheric gas burners, but it’s mighty fast and don’t have to sit from 9 to 5.
In either case, a heat source is necessary to roast beans. Quite simply, the roasting process is a process by which heat is transferred from the source to the coffee beans. The important portion of the coffee bean is the internal temperature and not the surface temperature of the bean. This is significant in determining the flavor that is brought out in the coffee. This becomes important because the two basic methods of roasting bring the bean to this point at different rates of heat transfer.
The significant difference between drum roasting and air roasting is in the rate of heat transfer. Air roasting has a much higher transfer rate (some say as much as two times) than drum roasting. It is this difference in time and temperature that creates a difference in flavor because the chemical change in the bean is achieved differently.
So what happens to the taste of coffee?
While the differences are many, for an amateur like me the primary difference is that the fluid bed roasted coffees tend to have a higher acidity. This means the aroma is very detectable. What this means in the cup is that it has a lighter mouth feel and less body. So you don’t have that strong after taste or a lasting impression.
Essentially the reverse of this is true for drum roasted coffees. Drum roasted coffees generally have more less distinct flavors in the cup, but have a much richer and fuller mouth feel. Drum roasters do have a greater ability to bring out the nuances of flavor.
Bottom line, drum roasting is akin to slow cooked meal, complex flavor levels, but a time consuming end product and is for a connoisseur. Air roasting is like making instant noodles, quick and efficient, end product enjoyed by all.