What are seasoning beans in coffee roasting?

Seasoning beans are low-value green coffees - typically past-crop stock, old samples, or cheap commercial grades - used to condition a roasting drum before you run any quality production coffee through it. When a drum is cold, or when a new machine hasn't been broken in, the metal surfaces haven't yet absorbed the oils that develop through regular use. Running a seasoning batch first coats the drum interior, stabilises the thermal environment, and burns off any residual smells from a cold machine.

Most roasters do this at the start of every session - one throwaway batch at temperature before switching to their production coffees. The seasoning batch gets discarded or, if it's turned out drinkable, used for staff coffee.

The principle is exactly the same as seasoning a cast iron pan. You wouldn't cook a good steak in a cold, uncoated pan if you could avoid it. The first batch in a cold roaster is the same logic - protect the coffee that matters by not making it absorb the machine's cold start.