formula to calculate O2 addition?

[laserghost]

Posted this first in the wrong forum (general brewing).

I haven't brewed in a while and am revving up for a brew day. One of the things I needed to refresh my memory on was how long I was running my pure 02 tank (through a .5 micron stone) to oxygenate the wort before pitching. I have a medical regulator on the tank and can control the flow down to .12 liters/minute. Historically, I think I'd run it at 1 liter/minute for 60 seconds for 5.5 gallons of 1.060 wort, and run it a little longer if it was a bigger beer, but it was mostly guess work, though the results were always good.

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Re-reading Chris White and Jamil's book, YEAST (pp 77–84, "How Much Oxygen Is Needed?") it states that for 5.3 gal of 1.077 wort, you would run oxygen at 1 lpm for 1 minute through a .5 micron stone to reach an ideal ~9.2 ppm dissolved oxygen. For higher gravity beers, or larger batches you would need to use more yeast, and therefore more oxygen.

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I was playing around to come up with a formula to accurately oxygenate a batch of wort based on volume and gravity, but I'm not really sure if this is solid or not. Maybe the actuals are not quite so linear? Any feedback is appreciated!

(this is assuming pure O2 run through a .5 micron stone at 1 lpm to reach ~9.2 ppm dissolved O2)

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FORMULA

(volume in gallons · gravity points) / 6.8 = time in seconds

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EXAMPLES

(5.3 · 77) / 6.8 = 60s

(5.3 · 57) / 6.8 = 44s

(15 · 67) / 6.8 = 148s

(.75 · 80) / 6.8 = 9s

yeast starter (.5 · 37) / 6.8 = 3s

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Thoughts?

 

[rhys333]

I honestly can't advise as to how much O2 is recommended using a tank, and at the risk of being a bit of a pest I'm going to offer a contrarian opinion. In my experience appropriate O2 levels are easily achieved without O2 equipment. Simple stirring, or just passing the wort though a fine mesh strainer (as I do), will provide more than enough to do the job well.

 

[IslandLizard]

It's more complicated. O2 absorption also depends on the height of the liquid (wort).

Using the "1 l/m for 60 seconds" guideline, I oxygenate a 5.5 gallon batch in a brew bucket at 1/4 l/m for 4 minutes, moving the wand every 30". In the beginning I still see a little bit of rippling on the surface, that becomes quickly covered up with foam.

Pitching enough cells (per yeast calculator) from a recent starter slurry or vitality starter, I always get fast lift off, usually within 6 hours.

 

[IslandLizard]

A few years ago, someone posted an Excel "Wort Oxygenation" calculator, buy I have no idea where he got the formulas from or what model it is based on. I tinkered with it, but settled on the 1 l/m for 1 minute model from Yeast, except I use it 4x as long at 1/4 of the rate.

 

[MaxStout]

There are a lot of variables as to how much O2 will be dissolved. Flow rate, size of apertures in the aeration stone, temperature, etc. Even the SG of the wort plays a part in how much O2 will be dissolved. Short of having test equipment to measure dissolved O2, the best you can do is guess. Running the O2 at a low flow rate, for a longer time (maybe a minute or more) will likely result in more going into solution. Higher flow rates tend to cause most of it to bubble to the surface.