Despite all of the years that drum roasters have been around, the technology has remained simple and relatively static. Essentially, a drum roller is a cylinder that is rotating on a completely horizontal axis. Paddles, vanes and flights will mix the beans, and heated air will move through the drum, effectively removing the roasting byproduct.
There are a couple different types of drum roasters. The design is made to provide more heat transfer, something you cannot get with a drum that is solid.
Why Drum-Roasters Are Always A Prevalent
The tangential is typically what is used in Europe for roasting, drum roasters are used throughout North America to roast roughly 70% of all of the coffee Beans that is produced. For many reasons, drum roasters are extremely popular in the US. First, these roasters have much smaller capacities, so they are more suitable for mid-sized and small businesses, or for larger ones that are able to roast coffee throughout the day, even simultaneously with multiple drum roasters. These tend to be more affordable, though they are not as fuel-efficient as other roaster types.
In fact, drum roasters are very popular for those that are in the specialty coffee industry because they have manual control options. Roast masters are able to manipulate the dampers, and also eyeball samples at the mid-roasting point, allowing them to achieve the best copy profile, similar to how a painter is able to use different pigments to create unique hues for the painting. If you are artistic, and you would like to apply this to the roasting process, a drum roaster is definitely what you want to use.
If you are going for dark roasts, drum roasters are the best ones to use and they are in high demand throughout North America, specifically in the US. You really can’t roast very quickly, and also achieve a dark roast simultaneously, without risking what is called a exothermic reaction; you have to slow down the entire process, allowing the flavor of the beans to fully manifest. When you are able to use a drum roaster, you can do all of this, usually with a single batch taking no more than 20 minutes. The reason this is possible is because the drum roasting mechanism utilizes less convective heat transfer, roughly 85%, in comparison to other roasters on the market today. Only 15% of the heat transfer, via conduction, occurs, plus there can be heat transfer between beans with a drum roasting unit.
As long as the beans are able to stay together while the drum is turning, it permits the liberal development of aroma, flavor compounds, and the acidity to transfer between the beans, allowing for a more flavorful end result. Roast masters are capable of manipulating these compounds in order to develop specific flavor profiles, creating a very artistic end result through the process.