As the title suggests: Does Concentrate Poison Stack with itself?

This is one of those weird questions that I honestly would have expected to have been asked somewhere, especially here, but I haven't actually come across anything in searching.

For Reference,

Concentrate Poison

The alchemist can combine two doses of the same poison to increase their effects. This requires two doses of the poison and 1 minute of concentration. When completed, the alchemist has one dose of poison. The poison’s frequency is extended by 50% and the save DC increases by +2. This poison must be used within 1 hour of its creation or it is ruined.

Source [Pathfinder SRD][1]

Now, I can see a few options here and I honestly don't know what it is supposed to be RAI. First, you can concentrate only once and it doesn't stack. Second, You can keep concentrating as long as you have doses of poison and make an unbelievably powerful one (I hope that isn't RAI)

Third is a more likely scenario. You can concentrate, but it is a recursive thing. IE: You need two doses of concentrated poison to concentrate it to the next level and two of that level to go on, etc. Now, with the one hour time limit, this method would force a permeable limit on how concentrated a poison can get. But, would the timer start again when you re-concentrated it or would it maintain the time it had before?

As a completely bonus question. What is the maximum concentration you could get a poison to and what would the cumulative effects be?

P.S. Despite my searching, it is entirely possible this question has been asked before. If so, I apologize. [1]: http://www.d20pfsrd.com/classes/base-classes/alchemist/discoveries/paizo---alchemist-discoveries/concentrate-poison