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Old 06-26-2013, 06:45 PM   #1
rubikcube
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Default Calculating Dissolved Oxygen

I am brewing a barleywine this weekend. Last time I tried barleywine, my fermentation stalled and I ended up throwing the batch out. This time, I am getting setup with a starter and oxygen system to avoid any possible problems. I have a welding O2 bottle, regulator, filter, and .5 micron diffusion stone.

My main question is how do I know once I have enough dissolved oxygen? I know that a lot of people say to just run the oxygen for 1 minute. I have also seen people who have bough meters to take measurements. However, I'm pretty sure there has to be a better way.

We can know the temperature and specific gravity of the wort and the partial pressure of the oxygen. Given these things, would it be possible to take a desired level of oxygen saturation, say 12ppm, and calculate a temperature at which a given wort would saturate to that level?

For example, if I knew that at 171 degrees my wort would max out at 12ppm on pure oxygen, I could stop my wort chiller at that moment and run the oxygen for several minutes to saturate. Once I feel reasonably confident that I am saturated (not exactly sure about this), I can turn off the oxygen and continue to chill.

Does this sound reasonable, or am I just crazy? If so, is there anyone who could help with the calculation?

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Old 06-27-2013, 02:21 AM   #2
ajdelange
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Originally Posted by rubikcube View Post
My main question is how do I know once I have enough dissolved oxygen? I know that a lot of people say to just run the oxygen for 1 minute. I have also seen people who have bough meters to take measurements. However, I'm pretty sure there has to be a better way.
Having a meter and measuring what you actually have has to be the best way. After a few runs you should know that running the regulator at 1/2 psig for 1 minute oxygenates X gallons of wort to Y ppm at a particular temperature.

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We can know the temperature and specific gravity of the wort and the partial pressure of the oxygen. Given these things, would it be possible to take a desired level of oxygen saturation, say 12ppm, and calculate a temperature at which a given wort would saturate to that level?
Yes you could do that but as you are going to oversaturate WRT atmospheric oxygen most people try to oxygenate as late as possible so that there is little opportunity for O2 that you went to so much trouble to inject to escape to the air. I, and many others, inject oxygen and yeast simultaneously into the line filling the fermenter.

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If so, is there anyone who could help with the calculation?
Do a web search on 'Henry Coefficient Oxygen' or consult a chemical engineering text or tables and, if lucky, you'll find the coefficient as a function of temperature.
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Old 06-27-2013, 12:06 PM   #3
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I, and many others, inject oxygen and yeast simultaneously into the line filling the fermenter.
How do you, and many others, inject the yeast?
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Old 06-27-2013, 02:41 PM   #4
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With a peristaltic pump. Have a look at the picture at http://www.pbase.com/agamid/image/84072882/large
which clearly shows the starter (in the carboy) and the pump (on the stool). The injection device is nothing more than a straight section of stainless steel pipe with a smaller piper welded into it with its end interior to the larger piper pointed downstream. Thus appears in the picture just behind my colleague's right wrist. It might be easier to select the 'original' size image in pbase and blow up the portion by his wrist. You can't see where the yeast line connects but you can see the handle of the valve (right hand one) which shuts yeast flow off. The white hose which appears to emerge from under Tim's left knee is the chilled wort line. Note that the other blue lever valve handle is for the oxygen injection valve which feeds the oxygen injector section which contains a sintered stainless steel 'stone'.

The peristaltic pump is the key. The injection device can be any of a variety off things. Even a simple Y should work.

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