The greenman's ale barrel can be built in the Barrel space of the Kitchen in a player-owned house. It requires 26 Construction and 29 Cooking to build and when built, it gives 184 experience. The player must have a hammer and a saw in their inventory to build it.
The barrel, when used with an empty beer glass, supplies the player with an unlimited amount of greenman's ale. The beer obtained from this barrel cannot be taken outside of a player-owned house.
This is one of the more useful ale barrels, as greenman's ale is one of the few ways to obtain a guaranteed boost for Herblore.