Take the Crudely-written Log to Kelek Skykeeper in southern Felwood.
The Winterfall are no longer a threat to me, but if you still want to find out what was driving the furbolg to create and consume this strange firewater, I think you should seek out Kelek Skykeeper.
He is part of a group known as the Emerald Circle, druids that are committed to their work in Felwood, healing the land from the corruption.
Kelek has much experience with the furbolgs in Felwood, and may be able to tell you more about the log.
Thank you, again, [player].