Spunding Valve Oxygen NEIPA Question

What is helpful to 99% of most all of us is that the “experts” (engineers, chemists, physicists, etc) break the hard, foreign language data into useable knowledge for the layman.

I have a medical background, masters in health administration. Those technical articles do nothing for me. I think 99% of brewers are not literate in that level of technical info.

Cheers to their expertise, happy to have it, more happy if it’s something I can understand.

 

Btw what is considered a “purge cycle”?

The decompression of entire keg to 0 psi?

Or 3 second burps? 5 second burps? Etc

 

Fully filling the keg and emptying it would be my guess. Seems like a massive waste of true.

 

By filling with Star San/H2O and pushing say a pint or two out then doing your purge cycles then continuing to push out the rest of the liquid you waste a lot less than doing full purge of an empty keg.

 

My understanding (bear in mind that I don't keg) is that a "purge cycle" consists of:

1. Attaching the keg to the CO2 tank and pressurizing it to one of the levels shown on the chart (e.g. 30 psi).

2. Disconnecting the keg from the CO2 (or at least cutting off the pressure) and venting the gas from the keg until it reaches 1 psi (or maybe slightly above).

As you do this cycle multiple times, the proportion of CO2 in the keg rises and the proportion of oxygen falls, since your CO2 tank is the only source of new gas for the keg. But some oxygen always remains, because you can't truly purge the keg of all gas, you can only bring it down to the level of atmospheric pressure (at least with this method). By doing multiple cycles, you can push the oxygen down to tolerably low levels, and the chart is meant to show you how many cycles you need.

To help make that determination, I calculated that you can multiply the number from the chart by 0.07, and by the number of liters of headspace in your keg once the beer is added, to determine the ppb of oxygen in your beer assuming (for simplicity) that all of the oxygen in the headspace dissolves into the beer. So for instance, if your keg has 1.5 liters of headspace, and you do 4 purge cycles at 25 psi, then there will be enough oxygen remaining in your headspace (after you rack in the beer) to add about 413 ppb oxygen to your beer. Here's the math:

3935 (from the chart) × 1.5 × 0.07 = 413 ppb

That is likely an overestimate, because not all of the oxygen in the headspace will dissolve into the beer, but it gives you an indication of how much oxygen you are dealing with. To put it into context, @TheBeerery's blog post claims that professional breweries commonly get their packaged beer down to 40 to 150 ppb oxygen. And that's dissolved oxygen from all sources, not just from headspace.

It occurs to me that astronauts actually don't need to push sanitizer through their kegs, they can just vent them to space. But on the other hand a kegerator is really heavy, and every gram is expensive to get into orbit, so they probably just bottle. Anyway if you are on the space station and you are kegging your homebrew, you can safely skip all this math.