Once you've completed Gertrude's Cat quest, she will Gertrude is going to give you adorable kittens. No charges or RS gold questions asked. There are no conditions included. Each kitten takes about three hours to mature. After that, it's eligible to exchange for Gertrude for 100 Death Runes or 200 once you've completed Ardougne Diary (easy) it seems odd, but it's the truth. You can keep mature cats in the bank and then turn them all in at once , if you want to be able to do so at your own convenience.
Level of Cooking Skill to 29. When you've mastered cooking up, get two bags from "the items" (reward of Trouble Brewing mini-game) four buckets of water four bushels barley malt Two ale yeast pots eight pinches of harrarlander as well as sixteen beer glasses that are empty and walk up to the top floor of Laughing Miner Pub where brewery is located.
Fill the vats (be attentive to the order you fill them with, it's essential) water, barley, "the stuff", harrarlander and cheap OSRS gold yeast then leave for anywhere from eight to two full days for it to ferment. Presto you've got yourself Two batches of beer ready for sale on the Grand Exchange!