The term used for the process of separation of grains from chaff is:
Wind winnowing is a method developed for separating grains from chaff. It is also used to remove weevils or other pests from stored grains.
In its simplest form, it involves throwing the mixture into the air so that the wind blows away the lighter chaff, while the heavier grains fall back down for recovery. This includes techniques like using a winnowing fan (a shaped basket shaken to raise the chaff) or using a tool (a winnowing fork or shovel) on a pile of harvested grain.