Was reading about oxygenating wort, and the book was saying that the best amount of oxygen ppm is 10. It did say that over oxygenating was sometimes bad, but didn't state how much it took before it started affecting the beer. Any ideas/experience? Thanks!
I will start by assuming you have an pure O2 tank, regulator, and wand/diffusion stone setup. Because it is impossible for you to over-oxygenate your wort by any method that uses air rather than pure O2.
I don't think there is a scientific consensus on how much oxygen is too much, and even measuring oxygen levels is a tricky business. I think there is consensus that 43 ppm of O2 is about the theoretical limit at which you reach maximum 02 saturation.
The drawbacks from over-oxygenating your wort are :
(1) Yeast Stress: Yeast will over multiply due to availability of O2, which causes stress in the yeast and can even reduce yoru ABV (because glucose is used in synthesis of cell components rather than metabolized into CO2 and alcohol. It is theorized yeast can also suffer oxidative stress and premature aging because the excess O2 leads to the creation of free radicals that damage cells.
(2) "Oxidation of Wort:" All of the oxygen may not be used by the yeast, and the remaining O2 will cause lead to oxidation of your wort. This effect is countered by the fact that O2 will leave solution in the wort and go into the headspace, and if the yeast start producing Co2, it will dilute the amount of O2.
That being said, the practical solution is that we know that the ideal O2 level is 9-18 ppm for most worts, and we know that a flow rate of 1L/min. through a 0.5 micron stone leads to a dissolved O2 level in that range in 60 to 180 seconds. SO if you control your flow and duration, you should be fine.