Oxidation while carbonating question, spunding

[Dland]

Thought I'd ask on this forum, as I know some of you know a bit:

If I am spunding in keg, with .006-.010 fermentation left to go, will beer absorb significant oxygen if keg not fully and completely purged? Beer will still be producing a fair amount of CO2, so there may be pressure out, but not sure that is how gas diffusion works. Also will remaining yeast activity consume any 02?

With lagers, ramps and D rest also done during spunding.

Reason I ask is I don't want to bother with full starsan displacement purge, mainly because my kegs have dip tubes shortened by 3/4-1 inch, and I do not want to leave all that starsan in there(yes, I know in theory it will not detract from beer). Also the full purge is somewhat time consuming & I have a couple dozen kegs in rotation.

I regularly do a partial purge and seal with CO2 to 10 PSI after keg sanitizing, which also assures keg is sealing well before fill. When kegs are filled there is only a couple of inches of head space, so not much gas left anyway.

Thanks for the help.

 

[Robert65]

There's no way around the need to properly purge.

Fortunately, it's dead simple to liquid-purge a keg with a trimmed or floating dip tube and get all the sanitizer out.

Trim the gas in tube so it is flush with or slightly recessed from the inside surface of the keg. After pushing out all the sanitizer you can through the liquid side, let a little pressure build. Invert the keg and position so that the gas post is at the lowest point in the whole system. Then pop on a gas disconnect and blow out the rest of the sanitizer through the gas post.

If you don't want to do this, your alternative is 16 full cycles of pressurizing to 30 psi and releasing. That's way more wasted time and gas to get the same result.

 

[IslandLizard]

your alternative is 16 full cycles of pressurizing to 30 psi and releasing. That's way more wasted time and gas to get the same result.

That! ^
And after the final gas purge likely still left with a higher ppm of O2 than a 100% liquid pre-purge would have.

Amount of CO2 needed (wasted): 16 x 5.5 gallons (keg volume) x 3 = 264 gallons of CO2.
That vs. the 6-10 gallons of CO2 needed for a single 100% liquid pre-purge. A factor 26-40 difference, per keg fill!

 

[Dland]

Thanks for the replies. Good idea trimming gas line(if needed, some kegs already flush w top of keg),

Not arguing that full displacement purge will leave less O2 in keg, just wondering about law of diminishing returns. I still have these questions:

Does yeast use any O2 in fermenting last .010 gravity?

Does fact that beer is "outgassing" CO2 limit oxygenation intake, even if only during closed transfer process?

When one is transferring prior to spunding, beer is still fermenting and releasing CO2 as it is pushed(by CO2) though the dip tube.

The volume of space occupied by gas at top of beer in keg is only equivalent to a pint or two, not the whole 5.5 gallons.