Author Topic: Oxidized DIPA -again...  (Read 1780 times)

Offline pointyskull

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Oxidized DIPA -again...
« on: January 15, 2018, 01:33:08 AM »
My second kegged DIPA is suffering what appears to be oxidation.
Keg was purged pre-fill, no splashing on transfer.

Here's my question:
I have been 'slow' carbing (11-12 psi over a couple of weeks) my homebrew kegs, as they share a C02 tank with some commercial kegs.

Question:
Does force carbing do anything to eliminate the potential for oxidation?
I know I am clutching at straws, but just trying to see if there is any homebrewer research on this.

I am frustrated, and googling like a banshee.

Offline Robert

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Re: Oxidized DIPA -again...
« Reply #1 on: January 15, 2018, 01:49:23 AM »
Quick vs. slow carbing won't change potential for oxidation; but if it takes a couple of weeks for symptoms to appear, time you're spending carbing, you'd at least get a week or so of drinking fresher tasting beer in.  That's all. Oxygen exposure (if you're sure that's the problem) is happening somewhere upstream in your process.
Rob
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Offline Robert

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Re: Oxidized DIPA -again...
« Reply #2 on: January 15, 2018, 02:24:08 AM »
^^^^
Just another thought as you trace the problem: you could still have oxygen pickup at kegging.  You say keg was purged, but if you mean you put on gas and "burped" the PRV a few times, there was lots of O2 in that keg.  The only sure way to purge is to fill to the brim with liquid (e.g. sanitizer) and push it all out with CO2.  There was a thread recently on the forum where a member posted calculations on "purging" by burping the PRV and your mind would reel at the number of cycles it would take!  You're also drawing air into the fermentor as you siphon beer out (if that's what you do) so you might search here on the forum for threads on "closed transfers." I've just gone that route.
Rob
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Offline pointyskull

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Re: Oxidized DIPA -again...
« Reply #3 on: January 15, 2018, 02:35:33 AM »
Thanks, Robert!

What psi do you use to do the sanitizer purge with C02?
 
fwiw the beer tasted great pre-siphon, but I will look into closed transfers, too.

I will investigate...

Offline Robert

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Re: Oxidized DIPA -again...
« Reply #4 on: January 15, 2018, 02:49:03 AM »
Psi doesn't matter, whatever will get liquid out.  You'll know liquid replaced air, and CO2 replaced liquid.  I say don't waste gas pressurizimg the keg too high when you'll just release it to add beer!

If it tasted great out of the fermentor, I bet you're on the right track here.  This point in the process seemed to be my Achilles heel. Purging the keg is probably the big problem, because air drawn into the fermentor is only making contact at the still surface.  But it's really easy to do a closed transfer (a carboy cap based rig to push low psi gas in and a racking cane leading to a QD to your keg) and if you like IPA, well, those hops sure do suffer from oxidation don't they! (Your LHBS has probably already helped others assemble the bits for closed transfer.)
Rob
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Offline klickitat jim

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Re: Oxidized DIPA -again...
« Reply #5 on: January 15, 2018, 03:00:04 AM »
Caution if using fermenters that don't play well with pressure. Like glass carboys..

Offline Robert

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Re: Oxidized DIPA -again...
« Reply #6 on: January 15, 2018, 03:05:17 AM »
Caution if using fermenters that don't play well with pressure. Like glass carboys..
ABSOLUTELY! When I say "low psi" I mean like 1 or 2.  I elevate my carboy above the keg, so I just need to apply enough gas to in effect start a siphon and then replace the volume of the draining beer.  It's slow but O2 free.
Rob
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Online denny

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Re: Oxidized DIPA -again...
« Reply #7 on: January 15, 2018, 04:47:41 PM »
Thanks, Robert!

What psi do you use to do the sanitizer purge with C02?
 
fwiw the beer tasted great pre-siphon, but I will look into closed transfers, too.

I will investigate...

These links might help....https://www.experimentalbrew.com/experiments/great-purge-does-full-liquid-purge-keg-protect-hop-aroma-better

https://www.experimentalbrew.com/purging-keg-etc-etc-etc
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Offline narcout

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Re: Oxidized DIPA -again...
« Reply #8 on: January 15, 2018, 06:40:33 PM »
I ♥ glitter beer

Offline The Beerery

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Re: Oxidized DIPA -again...
« Reply #9 on: January 15, 2018, 06:47:11 PM »

Here are the maths





You can see it's much more efficient to use sanitizer and push it out (10-12psi). Also trimming your gas diptube flush with the top wall of the keg and overfilling the keg in a closed transfer will be your best bet.
« Last Edit: January 15, 2018, 07:08:15 PM by The Beerery »
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Offline nbarmbrewer

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Re: Oxidized DIPA -again...
« Reply #10 on: January 15, 2018, 09:58:35 PM »
Remember heat speeds up oxidation or maybe your hops are oxidized.

Offline klickitat jim

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Re: Oxidized DIPA -again...
« Reply #11 on: January 15, 2018, 10:09:19 PM »

Here are the maths





You can see it's much more efficient to use sanitizer and push it out (10-12psi). Also trimming your gas diptube flush with the top wall of the keg and overfilling the keg in a closed transfer will be your best bet.
I'd be curious to see what 5, 10, and 15 seconds of 15psi on the out post would be.

Trimming the gas post... why haven't I thought of that?

Offline Robert

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Re: Oxidized DIPA -again...
« Reply #12 on: January 15, 2018, 10:27:19 PM »

Here are the maths





You can see it's much more efficient to use sanitizer and push it out (10-12psi). Also trimming your gas diptube flush with the top wall of the keg and overfilling the keg in a closed transfer will be your best bet.
I'd be curious to see what 5, 10, and 15 seconds of 15psi on the out post would be.
I've been looking over some past threads on purging.  It's been mentioned several times that there may be info on purging with a flow from the bottom, but nobody's posted a link. Anybody please?
  (Liquid still seems to me the surest thing.  Dalton' s Law and all.)
Rob
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Offline The Beerery

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Re: Oxidized DIPA -again...
« Reply #13 on: January 16, 2018, 12:12:08 AM »


Close to full oxygen when just flowing in. Gases don’t stratify, they mix.


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Offline The Beerery

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Oxidized DIPA -again...
« Reply #14 on: January 16, 2018, 12:15:42 AM »

Here are the maths





You can see it's much more efficient to use sanitizer and push it out (10-12psi). Also trimming your gas diptube flush with the top wall of the keg and overfilling the keg in a closed transfer will be your best bet.
I'd be curious to see what 5, 10, and 15 seconds of 15psi on the out post would be.
I've been looking over some past threads on purging.  It's been mentioned several times that there may be info on purging with a flow from the bottom, but nobody's posted a link. Anybody please?
  (Liquid still seems to me the surest thing.  Dalton' s Law and all.)


You mean like this?

“So, what happens if instead of doing pressurize/vent cycles, we flow CO2 into a vessel that originally contains air?  Does the flow improve the dilution and removal efficiency of O2 compared to the cyclic process?  We can argue that if the CO2 inflow is fast enough that CO2 comes in faster than it can mix with the air, then it could form a sort of gas piston that would push air ahead of it towards the vent, and that this would push out more O2 per volume of CO2 than if complete mixing of incoming CO2 and existing gas occurred (as it does in the pressurize/vent case.)

The best case for non-mixing of CO2 and headspace would be if there were absolutely no internal "air" currents, such that the only mixing of CO2 with headspace gas would be via diffusion.  So the question comes down to: Is the linear CO2 flow rate faster than the diffusion velocity of CO2 in air? If the CO2 flow rate were much faster than diffusion, then mixing would be limited, and continuous flow would be more efficient than purge/vent.  If CO2 flow rate were much slower than diffusion, then gases would be mostly mixed, and continuous flow would not be any more efficient than pressurize/vent.  If the flow rate and diffusion rates were of the same order of magnitude, then there would be significant, but not complete, mixing, making this the most complex scenario to analyze.

To start we need to get an estimate of the diffusion velocity of CO2 in air.  If we limit our analysis to one dimensional flow (say from bottom to top of a keg, uniform velocity across the width), things will be much simpler, but still valid.  Fick's first law of diffusion is (ref: https://en.wikipedia.org/wiki/Diffusion):[indent]Flux = -D * (ΔConc / ΔDist)
Where Flux is in mass/area-time,
D is the diffusion coefficient, and
ΔConc / ΔDist is the concentration gradient[/indent]If we divide Flux [mass/area-time] by density [mass/volume] we get linear velocity [dist/time] which is what we are looking for.

The diffusion coefficient for CO2 in air is about 0.15 cm^2/sec (ref: http://compost.css.cornell.edu/oxygen/oxygen.diff.air.html)  Now if we make some assumptions about gradients we might encounter, we can estimate a linear CO2 flow rate due to diffusion.  We will use approximate numbers for simplicity, since we are only looking for order of magnitude estimates of velocity.

A corny keg has a volume of about 20 L or 20,000 cm^3, and a height of about 55 cm, leaving a cross sectional area of about 20,000 cm^3 / 55 cm = 364 cm^2.  The density of CO2 at STP is about 2 g/L or 0.002 g/cm^3 (ref: http://www.engineeringtoolbox.com/gas-density-d_158.html.)  If we assume 2.5 cm of pure CO2 at the bottom of the keg, and 2.5 cm of air at the top of the keg, and a uniform concentration gradient from the bottom to the top, the CO2 gradient becomes:[indent]ΔConc / ΔDist = (0 - 0.002 g/cm^3) / 50 cm = -4.0e-5 g/cm^4[/indent]The CO2 flux becomes:[indent]Flux = -D * (ΔConc / ΔDist) = -0.15 cm^2/sec * (-4.0e-5 g/cm^4) = 6.0e-6 g/cm^2-sec[/indent]And finally the linear velocity of CO2 due to diffusion is:[indent]CO2_Diffusion_Velosity = CO2_Flux / CO2_Density = 6.0e-6 g/cm^2-sec / 0.002 g/cm^3 = 0.003 cm/sec[/indent]



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