Not to be confused with Apple barrel.
Apple Barrels are found at the two breweries in 'The Laughing Miner Pub' and 'The Green Ghost,' which are in eastern Keldagrim and Port Phasmatys, respectively. They are used to create apple mush by using four cooking apples on it while having a bucket in the inventory. Apple mush is used in brewing cider.
An apple barrel is also found in the apple orchard just outside the Tree Gnome Stronghold. While it is primarily used during the quest Mourning's Ends Part I to create a rotten apple barrel, it can still be used to create regular apple mush.

A player mushing apples in an apple barrel.