I use the hardware store O2 cylinders and a 0.5 micron stone. I talk about the (admittedly somewhat subjective)formula for seconds of O2 I use in this thread... http://beeradvocate.com/community/threads/recap-2012-the-good-the-bad-the-bubbles.56165/#post-751600 And yes, you can over oxygenate.
Silly question from the previous thread: Does over oxygenation pre fermentation taste the same as oxygenation post fermentation? I don't think that I've had any problems with my beers, but I tend to stay way from brewing hop bombs and do a good job of transfering post fermentation.
use a sintered stone if you can. it is just about impossible to measure the actual dissolved O2 concentration in liquid without a meter. so unless you have $700 and lots of patience calibrating and maintaining the meter, don't sweat it. just blast it for 30 seconds or so (I actually have use of a good O2 meter and choose to skip it. they are that much of a hassle to use). a good trick is to move around the stone in the wort as you inject O2. if you see a lot of bubbles rising out of the liquid it means your gas is not dissolving into the wort but escaping into the atmosphere. move the stone around as you inject and the oxygen goes where it is supposed to. the risk of over oxygenating is real, though it is generally accepted that not enough O2 is a much greater problem then the small possibility of over oxygenating homebrew. Cheers.
over oxygenated wort (not beer) is sometimes described as having a yeast bite, whatever that means. no, it is not the same as the "wet cardboard" profile for oxygenated beer. I wouldn't know over oxygenated wort, but my understanding is that the yeast will remain anaerobic for too long while they suck up all the available O2 and this can lead to some fermentation problems later on. but I believe I can count on my thumb the amount of posts I have read regarding the problems of over-oxygenating homebrew wort, so how real a concern is it? that's just me though. Cheers.
From Yeast: Pure O2 delivered through a 0.5 micron stone at 1L/min gives these results to 20L of wort at 75F: 30 secs - - 5.12 ppm 60 secs - - 9.20 ppm 120 secs - - 14.08 ppm Over-oxygenated wort can create bad flavor problems, but according to White Labs and Wyeast this is not a big concern. http://www.wyeastlab.com/hb_oxygenation.cfm
