Drum roasters are designed for smaller batches and artisan roasters. Machines start at 1kg and go up to 120 kgs in drum size. As a rule of thumb one can say that the larger you get, the more you lose the ability to bring out detailed flavours. Intrinsic heat and the larger batch sizes are the reasons for this.
We roast on a 25kg roaster by Probat, Germany. The double drum gives us an air pocket between the metals, passing on heat very gently to the beans. We have a flat oxygen-gas burner for efficient energy supply (and lots of it!), airflow control, and an enlarged cooling tray for full control of our roast cycles. As an addition we have drum speed control (for smaller batches) and a de-stoner, on the off-chance that there are any small stones in our green beans. This rarely happens, but we want to be extra sure this will never be the case.