I killed Corien 70 times, 3 times he dropped [Swift Brewfest Ram] and 4 times [Direbrew's Remote]
BUT, he dropped it ONLY when his Mole was active.
The mole spawns from the ground, then will be active for 5 seconds and then will start rotating and goes back to the ground.
Maybe you have to kill him when his Mole is active
Sorry for bad english