Through my time of being a coffee roaster, I have found an important relationship between specialty coffee, time, the roaster size, and its capasity.
Fast food chains need their money, and the people need their coffee. As a result, mass production of coffee, and roasting coffee in large volumes may result in unmanageable time and inconsistent data, and an undesirable beverage (unless it is packed with milk and sugar). I would consider this to be called commercial roasting or "big batch" roasting.
While "big" roasters may look better, the performance is not always reliable compared to "littler" roasters. Larger roasters are difficult to operate considering the limited time the roaster has to profile the coffee until the coffee is dropped, burned, baked, or destroyed. Quality roasting profiles are of vital importance to a finished product when it comes to roasting coffee. Especially specialty coffee.
Every roaster has different maximum capacities. The maximum capacity is the amount of green coffee the roasters drum is capable of holding. Roasting the maximum capacity, and or "overloading" is dangerous. Choosing to roast such a way will over-expose the beans to heat, slow the drum speed, significantly slow air flow, disatisfy the bean thermal probe, and ultimately break the roaster.
So, what is the correct capacity for a roaster considering a roasters size, material makeup, and the maximum capacity assigned to the machine? I have heard anywhere from 50%-80% of the maximum capacity. Personally, 70-80% is my comforatbility spot.
As far as providing a cup of coffee to meet top requirements, small-batch and micro-roasting have shown to provide the best results, thus maintaining the integrity of specialty coffees, and sensory roasting.
