I don't think cooking level is a factor, nor cooking experience with a particular ale. My very first batch of anything that I brewed was Chef's Delight and it was a Mature batch!! I didn't realize it was special until I brewed the next batch, which came out normal. Cooking level was in mid-60's. After about 18 more batches of Chef's Delight I obtained another Mature one. After about 30 total, now at cooking level mid-70's, those 2 are all i've had so far. A friend with cooking level 61 obtained a batch of Mature Axeman's Folly after 2 normal ones and 1 batch of normal Chef's Delight - these were the first ales he had ever brewed. Since then he has brewed 2 more Axeman's and 3 or 4 more Chef's, no more Matures. Even though the occurrence is "random", anyone who has done programming knows that the event has to have a probability attached to it. If they would bother to find out from their programmers, Jagex could tell us what the chances are - 1 in 100? 1 in 1000? There must be a number-factor in the program somewhere, which determines that. [pokemama edit 10/5: unfortunately, Jagex prefers to keep players guessing - when you find out the system for the Ring of Wealth, please let us know, lol! Remember that "The Stuff", which can be bought from Honest Jimmy using Pieces of Eight from the Trouble Brewing game, improves the chances of brewing Mature ale to 50% (a fact actually provided by Jagex!) A Crewbie doing a large amount of brewing for other research has verified the 50% as accurate. It took me about 3 batches before I struck mature, but it has been pretty even for me since then.]