Separating the wheat from the chaff
Distinguishing between quality and worthlessness.
This one is biblical and can be found in Matthew 3:12, where John the Baptist says, ‘His winnowing fork is in his hand, and he will clear his threshing floor, gathering his wheat into the barn and burning up the chaff with unquenchable fire.’
Chaff was only good for animal feed. Wheat fit for human consumption.