I'm changing things up a bit here. I'm having a heck of a time getting predictable oxygenation with the oxygen stone. It's just not that consistent. So, the new idea is instead of oxygenating the wort, lets try oxygenating the fermenter head space.
I picked up one of these drill mixers things. It's kind of spiffy. It's folds down to fit inside the carboy and fans out when spinning. This thing really whips up the liquid. I did some tests with water.
Water just splashing into the fermenter from the faucet came in around 3-3.5 ppm. Note you brewers who just "fan" the wort into the fermenter. That's probably not doing the job. I then used my cordless drill at ~600 RPMs to stir. I put a stopper on the stirrer to seal up the fermenter. The thinking here is to avoid sucking in a bunch of air to contaminate the beer, but also an attempt to control the O2 levels. I don't want to get a bunch of O2 into solution to just have it degas out if I can help it.
After about two minutes, I got about 8 ppm in the water, which is about spot on. This should be perfect for ales. Note that this is just water, and could be lower with wort. With that stopper holding things back, I think the head space only holds enough O2 to do about 6-7 ppm, so I did it twice one minute each. Between spins, I pulled out the stirrer. That seemed to get me my 8 ppm the quickest.
I then emptied the carboy and started again. This time I put the O2 hose into the neck of the carboy and gave it 10 psi for 15 seconds. I stirred for 30 seconds, and it was 20+ ppm. That was fast...
I tried few more times, and came down to using 5 psi for just a second or two w/ 30 seconds of stirring gave me 12 ppm. Perfect. If I did the same spurt of O2, but did 8 ppm with just air first, that gave me 14 ppm. I did this a few more times and was pretty consistent. Again, this will likely change with wort, but I think I've got my ball park solution.
What's remarkable is how very little O2 is needed to get oxygenation. Just a spurt is all it takes.
Oh, and this thing is great for cleaning kegs too! I fill with cleaner, swirl it up and let it sit.
04-15-08 UPDATE: I used this on wort tonight. Two batches of German Pils at 1.044. I used just aeration for 2 minutes, and that gave me 8.3 ppm. I then gave the second fermenter my 1 second whiff of 5 psi O2, and stirred for 30 seconds. That gave me 11.6 ppm. I wanted to go a just a little higher, but I called it good. Next time maybe try two seconds of O2.
I'm pretty happy with this solution. It's pretty consistent and gets what I want on my first try. No fussing around.
04/29/08 UPDATE: I ran this on the recent Flanders Red, which was about 1.068 or so. I got 7.7 ppm, so we're starting to see the affects of original gravity on dissolved O2. At this point, the yeast should also have higher O2 requirements, so we have inverse conditions working against us. For my own brewing, I might call 1.065-1.070 the break point for aeration on ales. From there, I may want to start giving some O2 to the head space.
06/29/08 UPDATE: Just a quick update on the technique. I'm having great results doing this. Since I first tried this, I've got 13 batches in. What I've settled in with is I shoot for 12-16 ppm on all beers, just to make things easy. I'm not seeing anything negative on ales or lower gravity ales at those levels, so I'm going with a unified technique. What I do is I give the wort 3 seconds of O2 at 5 psi, then mix for 20 seconds or so. That gives me somewhere between 14-15, with some variations on wort gravity.
Comment feed for this post
A cheap and easy way to aerate and oxygenate wort.
Quick question, you said:
I think the head space only holds enough O2 to do about 6-7 ppm, so I did it twice one minute each.
Between each 1 minute treatment, did you just let it sit or slosh it about?
Cheers.
What I did for just aeration, I stirred for a minute. remove the stirrer, pulled a sample, and got my results, then went back. It seems with that, O2 diffused into the head space to finish the job. Other times I went for 2 minutes and didn't get the target 8 ppm, but removing the mixer and restarting it got me there.
Great experiment. It really shows that only little O2 is needed to get to 8 or 12 ppm DO. I don't have a DO meter (certainly wish I had ;) )or a flow meter on my O2 system, but may want to make a mark on the regulator nob that allows me to keep the setting the same everytime I oxygenate.
I (had to) run some numbers and 10ppm O2 in 17l of wort (avarage fill for a 5 gal carboy) require 170mg of O2. At atmospheric pressure, this is about 240 ml (~1 pint) of pure O2 (molaric volume = 22 l/mol; molaric mass = 16g/mol) and a little over 1qt of air. The 2 qt of head space in the fermenter do seem good enough to get to 8 ppm since not all the O2 will end up in the wort.
I like the fact that your experiments are in line with a quick calculation of the O2 volume needed.
When you say 10 psi O2 into the fermenter, did you pressurize the fermenter or did you just hold the hose into the opening, assuming that the pressure will lead to a particular flow rate of O2?
Kai
As far as adding the O2, no the the carboy isn't pressurized. That would be bad. What I am doing is I'm setting my O2 to 5 psi, then I just stick the hose into the neck of the carboy for 1 second, or what I call a whiff. As I mentioned, it seems 2 seconds might be closer to ball-park 12-14 ppm.