Spunding Valve Oxygen NEIPA Question

Ah. I see what you're getting at. To me, the answer then is to fix the numbers, not to discard the concept.

Is there something about the model that bothers you? Or is it just that it hasn't been tested with kegs? IIRC, NASA tested the "purge equation" (which I assume the chart used) with other gases (in their case, they were purging with O2, not trying to eliminate O2) and found it to be pretty good. Though my memory could be faulty.

 

I thought I would spell out my math and give a simple factor that you can use if you want to translate the chart into parts per billion of oxygen in your beer (see important assumption below). You can ignore this unless you are curious how I got my numbers earlier.

If you want to know how many parts per billion of O2 would be dissolved in your beer if the oxygen in the headspace fully dissolved into 5 gallons of beer, you can use the following factor:

0.07 ppb of O2 per liter of headspace in the keg, per ppm of O2 in the headspace

So in other words, take the liters of headspace in your keg (the space above your beer), multiply it by the ppm of O2 in the headspace per the infamous chart, and then multiply it by 0.07 to get the ppb of oxygen in your beer assuming it all dissolves.

I give my math below so that people can check it if they want. But first I want to note an important assumption I am making, which is that the oxygen fully dissolves into the beer. That's not entirely realistic since some will remain in the headspace in equilibrium. But as oxygen bonds with compounds in the beer, more oxygen should enter solution to restore the balance between oxygen in the headspace and oxygen in the beer. So you can think of these numbers as a sort of worst-case scenario, but one that should correspond to the amount of damage the oxygen will do to your beer.

First, we have to know how many moles of gas there are in a given volume, because the chart expresses oxygen concentration in parts per million. I used the ideal gas law P=nRT/V to calculate n (number of moles of gas).

P = pressure in atmospheres
n = number of moles of gas (a mole is Avogadro's number, it is a measure of the number of atoms or molecules)
R = a constant equal to 0.082057 liter-atmospheres per mole-degrees Kelvin
T = temperature in Kelvins
V = volume in liters

I assumed a pressure of 1 atmosphere, a temperature of 293.15 Kelvins (which is 20°C or 68°F—remember, this is the temperature of the gas in your keg while you are purging), and a volume of one liter. Plugging those numbers in, I got 0.04 moles per liter of gas.

That gives us the total number of moles in a liter of gas at room temperature and normal pressure. How many moles of those molecules will be O2? That's what the chart tells us. You just have to divide by a million because the chart is specified in parts per million.

As noted above, I am assuming that all of the oxygen in the headspace gets dissolved into the beer. So we simply take the moles of oxygen that we've calculated and convert them to grams by multiplying by 32. Then we divide 32 grams into 18.9271 liters (5 gallons) of beer, which we assume weighs 1010 grams per liter. (Water weighs 1,000 grams per liter and beer is a bit heavier than water as reflected by a typical FG of about 1.010.)

That gives us parts of oxygen per part of beer, and then we multiply by a billion to put it into parts per billion. I calculate it at 0.07. Remember, that has to get multiplied by the volume in your headspace and by the appropriate number from the chart.

 

Better? Used better numbers for O2 concentration in air and for the PSIs equal to 1 atmosphere (embedded in the formula). Terminology Tweak. And more reasonable significant figures.

 

Slight quibble, I think this is still ppm of O2 on a volume basis, not molecules of O2 per liter.

 

Doh.

 

Except for the simple fact you overlooked atmospheric pressure vs absolute pressure.

To calculate the headspace contribution to TPO use the following formula:
TPO = Headspace Vol * Headspace ppm O2 / Total Package Vol
A 5 gal ball lock keg has a total volume of about 5.3 gal. If volume was 4.7 gal, headspace volume was about 0.6 gal. If You did 3 purges at 10 psi, then the TPO contribution, just from the headspace, is:
0.6 gal * 44,267 ppm / 5.3 gal = 5011 ppm
If purges were done at 30 psi, then the TPO contribution is:
0.6 gal * 7469 ppm / 5.3 gal = 846 ppm
Too much O2 in either case.

 

I'm not sure I understand what you're saying, and quite possibly I'm misunderstanding.

But to the extent I understand, I think you're wrong. Parts per million is unitless, but it means different things in different contexts. In particular, you can't assume that parts per million translates seamlessly from gas to liquid. When oxygen is in gaseous form, we generally use ppm to mean the abundance of oxygen relative to other gases as measured by volume or pressure (this corresponds to the total number of moles of oxygen, and oxygen's molecular weight is irrelevant). But when oxygen is dissolved in a liquid, we use ppm to mean the mass of oxygen relative to the overall mass of the solution, and at that point its molecular weight is highly relevant. To translate between these it's necessary to do math along the lines I described above.

But again, maybe I'm just not following what you're saying.

 

Perfect.

This is a long way to get to an accurate chart, the one that should have been presented in the first place (and thanks for doing the math because math).

As far as the purge concept vs. purge reality, yes the mathematical model would seem to suit our needs. No doubt. The conversation took a detour but it is important.

However I am concerned that this basic data, the foundation for everything else, was not even accurate when it was presented as "See, this chart proves my point". No it doesn't.

Trying to unbury the data by throwing out some other equations, in an authoritative manner, leads me to the same conclusion as usual.

The concepts may be real and valid but the presenter is lazy, mis-informed or worse, full of shit on occasion, and demonstrably incorrect. Everyone is entitled to their own opinion. But no one is entitled to their own facts.

That is mostly opinion but not entirely. And I am cranky.
Cheers.

 

Suck it up buttercup.

http://web.mnstate.edu/marasing/CHEM102/Chapter Notes/Ch_01 ho.pdf

 

Thanks for the insight.
This really doesn't get started until page 101 but I think it is evident without getting into the weeds.



http://www.unc.edu/math/Faculty/met/complex.pdf

 

When I looked up the “purge equation” some time ago there were some papers that had the theoretical curve along with experimental data points. Those data were close enough to say that the purge equation is useful.

My conclusion was that to get down to a best practice of low O2 levels I would be wasting a lot of CO2. I fill with sanitizer and push that out with CO2 now. A guy in my club told me about that technique back around 2000, so it is not new.

 

Jeff, do you have a link or a reference to a paper with those curves? I would be interested in reading about this.

Cheers!

 

No. They were on line, from a University IIRC.

 

A few points.

1. I don't see why the "purge equation" is controversial. It's a straightforward extrapolation from the assumptions. Let's say I've got a bag with 100 marbles in it, 21 of them red and 79 of them black. Then I add 200 black marbles and shake the bag thoroughly, so that the marbles are randomly assorted. Then I remove 200 marbles. Then I add 200 more black marbles and shake. I repeat as many times as I think sufficient to reduce the expected number of red marbles to an acceptable level (which is a subjective question). The chart just tells me how many red marbles I should expect in the bag after N cycles. I don't see how anyone could argue with the math here, unless you disagree that the purged gas is proportionate to the aggregate gas in the keg (that is, you aren't disproportionately purging any particular gas). The reason the chart has different columns is that at different pressures you are adding different amounts of CO2 (the black marbles in the analogy—note that in my analogy, all non-oxygen gases, most notably N2, are also represented by black marbles). Of course one big difference is that instead of 100 marbles we have more like 0.8 moles of gas molecules, a truly huge number, meaning that we're not going to see nearly as much variance in the proportion of oxygen molecules removed in each cycle.

2.

I think if we're going to have a reasonable discussion, stuff like this is unhelpful. First, the tone is obviously disrespectful. But more importantly from my perspective, I can't tell what this is meant to establish. I can't see that it has any relevance to the discussion, and I'm not going to spend a bunch of time trying to figure out what you might be driving at. A while ago @VikeMan speculated that LODO was controversial because "HSA proponents rarely take the time to frame the discussion in terms of a good-better-best continuum or a marginal improvement type of scenario, and HSA sceptics feel like they are being told their beer sucks." I would suggest that another plausible explanation is that HSA proponents often appear to be more interested in dunking on their interlocutors than they are in presenting their ideas helpfully and clearly. I thought your recent BYO article was great and I wish you would carry that spirit into these forums.

3. If I've made some mistake in my math please point it out with specificity.

 

So its totally cool for Bill to continually take personal shots at me, over a topic that he is clearly wrong about, and the minute I back up my data. I get blasted?

THIS is the problem, it's totally cool for everyone to burn the witch, but the minute the witch fights back he is shamed.

It's nothing new, it's been this way from day one, however it's now been 3 years and its getting quite old.

Once again, I did not make the chart, HOWEVER, the chart IS correct, as is the so called "irrelevant" link
210000.00 IS THE NUMBER.

 

I'm pretty certain 20.95% is the accepted average number among chemists/physicists and that the document you linked simply used the oft-quoted rounded number (the one I can remember hearing in high school chem) of 21%. Rounding to 21% doesn't particularly bother me, as I think the concepts are the more important thing here, and 21% is pretty dang close to 20.95%.

Old Timers know I enjoy a spirited debate, but it's a shame there has to be a name-calling peeing contest (on both sides) over this issue, or over whatever has gone down in the past, but there it is. <Cue Rodney King.>

 

At 2:48 he'll mention purging. I assume this is what all brewery's do instead of filling with water/sanitizer unless this is done when cleaning.

 

English?

Are you a mathematician?

 

This is just the same pissing match that's been going on for a while. It's really annoying because both participants provide a lot of expertise to the forum, and have a lot to add, and yet it's like cats and dogs whenever they interact. Personally I would like to see a deescalation. It's not about allocating blame, it's about being able to coexist on a forum where both participants are valued for their knowledge. This shit makes it really unpleasant.

 

In order to avoid any real work on this Saturday morning, I went ahead and added a PPB section to my version of the chart. Engineers/Chemists/Assorted Geeks will note that I have made no attempt to resolve significant figures...I simply rounded spreadsheet answers to the nearest whole numbers. If someone would like to remove slop, please have at it.