An Asgarnian ale flatpack can be made at a workbench (Wooden workbench or better) in the workshop of a player-owned house. Like when making the normal Asgarnian ale (barrel), this requires 18 Construction, uses 3 oak planks, 8 Asgarnian ales and gives 184 experience. The flatpack can then be used on a beer barrel hotspot in a Kitchen.
