This probably refers to roasting in traditional drum roasters in batches.
There are basically two methods of roasting employed by commercial coffee roasters.
1. **Drum roasting**. Basically a Drum is heated from below and revolted to stir and mix the beans to heat them evenly. This takes about 15-20 minutes, depending on the desired darkness of the roast.
2. **Hot Air roasting**. Here the beans are heated by hot air and reach target temperature much quicker. This can be implemented in a continuous process for industrial scale production. Roasting times go from 3-6 minutes.
Both methods have their advantages and disadvantages. Most obvious is the different roasting time, which advocates of the drum-roasting claim to give the chemical processes in the beans more time to develop the flavor.
From a roasters perspective:
* Neutral reference
* Pro Small batch drum roasting
* Pro hot-air roasting