Ale yeast is an essential ingredient for brewing ales as part of the Cooking skill. Yeast is the final ingredient that must be added to a vat, and begins the fermenting process, which can last anywhere from two to four days.
Players can purchase ale yeast from one of two brewing assistants found in breweries. These assistants are Blandebir, who can be found in the Laughing Miner Inn in the dwarven city of Keldagrim and charges 25 coins; and Metarialus, who is found in the basement of The Green Ghost inn of Port Phasmatys and charges 5 ecto-tokens (the amulet of ghostspeak is required). Players must also have an empty pot in their inventory to put the yeast in.
In Keldagrim, a pot can be found respawning near the vat and you can fill it from Blandebir for 25 coins. More can be purchased from Gunslik's Assorted Items in Keldagrim Palace. In Port Phasmatys, they can be purchased from the General store.