Elixir Master
From WoWWiki
Elixir Mastery is a specialization of Alchemy. It allows an alchemist to sometimes create an additional elixir when brewing elixirs. Note that this effect also applies to the creation of Flasks, which are considered a variation on elixirs.
Notes
It appears that the benefit (over time) is about a 25% increase in the number of elixirs created. Each time it procs, it may result in some number of extra elixirs, typically 1-3 extras (IE 2-4 total), but getting as many as 9 extra has been reported.
It has been reported to proc even on "Grey recipes", indicating that the difficulty level, and perhaps the item level, of the recipe has no influence on whether or not it occurs.
Patch 3.1.0 doubled the amount of flasks produced by all recipes. There have been reports that this doubling also applies to the number of bonus flasks from Elixir Master, if true, this would mean that bonus flasks are now always created in multiples of 2.
Obtaining the Elixir Master specialization
This specialization is directly obtained by completing the quest 
[70] Master of Elixirs from Lorokeem <Grand Master Alchemist> at the Shattrath City. You must be at least level 68 to be offered this quest.
An alchemist who has specialized in one of the other two specializations can switch to this one by talking to the quest giver of their current mastery and pay a 150g fee. The character then has to talk to the quest giver of the mastery desired and instantly get the new mastery. This is possible only after the character has completed the quest to gain one or another of the Mastery abilities.
