Cold crashing and oxidation

[olotti]

Using a three piece airlock if there's still solution in the airlock even if it's just say down to the last 1/4 of the airlock is it still possible to get oxidation. I would think thasolutiokn would still be forming a barrier but just curious.

 

[doug293cz]

When you cool the fermenter, the pressure of the gas in the headspace drops due to the temp change, and additional CO2 absorption by the beer. This creates a negative pressure in the headspace relative to the atmosphere, so the airlock will bubble "backwards" letting air into the fermenter. Doesn't matter if it's a three piece or "S" airlock.

Brew on

 

[GHBWNY]

Using a three piece airlock if there's still solution in the airlock even if it's just say down to the last 1/4 of the airlock is it still possible to get oxidation. I would think thasolutiokn would still be forming a barrier but just curious.

If the solution drops below the bottom edge of the inside cup, it's definitely letting air in, and even if it's above the bottom edge, but not up to the mid-line, it could possibly suck solution back into the fermenter. It's not as likely toward the end of ferm as activity slows down. But it's during post-ferm when oxidation is more of an issue.

 

[olotti]

When you cool the fermenter, the pressure of the gas in the headspace drops due to the temp change, and additional CO2 absorption by the beer. This creates a negative pressure in the headspace relative to the atmosphere, so the airlock will bubble "backwards" letting air into the fermenter. Doesn't matter if it's a three piece or "S" airlock.

Brew on

Ok I think this may be my problem. I've had oxidation issues with 3 of my last 4 IPAs and dipas especially, I've had some issues in the past but it was never every beer. they each had 3-4 day cold crashes in my fridge where the solution in the airlock def dropped but there was always a little solution still in the airlock, I thought I was ok. I go to great lengths not to add any unnecessary O2 when bottling so this was the only step I could think of that was causing this issue. Guess I'll quit cold crashing and just figure things will drop out when letting the bottles sit in the fridge.

 

[freisste]

Ok I think this may be my problem. I've had oxidation issues with 3 of my last 4 IPAs and dipas especially, I've had some issues in the past but it was never every beer. they each had 3-4 day cold crashes in my fridge where the solution in the airlock def dropped but there was always a little solution still in the airlock, I thought I was ok. I go to great lengths not to add any unnecessary O2 when bottling so this was the only step I could think of that was causing this issue. Guess I'll quit cold crashing and just figure things will drop out when letting the bottles sit in the fridge.

I've come to the same conclusion with my beers.

I read a similar thread earlier where someone was talking about a few myths (which I had wholeheartedly believed), including the "stable layer of CO2" which would protect your beer, etc.

Like you, I will no longer cold crash (outside the keg).

 

[55x11]

Ok I think this may be my problem. I've had oxidation issues with 3 of my last 4 IPAs and dipas especially, I've had some issues in the past but it was never every beer. they each had 3-4 day cold crashes in my fridge where the solution in the airlock def dropped but there was always a little solution still in the airlock, I thought I was ok. I go to great lengths not to add any unnecessary O2 when bottling so this was the only step I could think of that was causing this issue. Guess I'll quit cold crashing and just figure things will drop out when letting the bottles sit in the fridge.

I wouldn't rush to blaming cold crash procedure.
How do you transfer the beer to keg (or bottle)? That may be more crucial.
Why are you cold-crashing for 3-4 days? It takes a day or so to cold crash for me.

One thing you may want to try is: attach a balloon to the neck of fermenter to capture CO2 escaping from fermentation, a day or so before cold crashing. When it is inflated, cold crash - CO2 from balloon will go back into the headspace. Or just flush the headspace with CO2 if you have kegging setup as you are cold crashing.

in my opinion, exposure to mix of CO2 and oxygen for ~24 hours while its cold crashing is NOT the reason for oxidized beer. If this was the case, every home-brew in the world was oxidized.

It's more likely something else in your process. Like bottling/kegging.

 

[murphyslaw]

I wonder whether the amount of air that gets sucked back in is enough to cause significant oxidation.

 

[olotti]

I wouldn't rush to blaming cold crash procedure.
How do you transfer the beer to keg (or bottle)? That may be more crucial.
Why are you cold-crashing for 3-4 days? It takes a day or so to cold crash for me.

One thing you may want to try is: attach a balloon to the neck of fermenter to capture CO2 escaping from fermentation, a day or so before cold crashing. When it is inflated, cold crash - CO2 from balloon will go back into the headspace. Or just flush the headspace with CO2 if you have kegging setup as you are cold crashing.

in my opinion, exposure to mix of CO2 and oxygen for ~24 hours while its cold crashing is NOT the reason for oxidized beer. If this was the case, every home-brew in the world was oxidized.

It's more likely something else in your process. Like bottling/kegging.

I bottle so I cold crash that long to really clear any yeast, maybe it's to long as most of the dry hops have settled by the time I bring my fermenter upstairs to the cold crash fridge, my basement where I ferment is around 64 deg ambient. I think now I didn't cold crash a couple beers back when I wanted to make NE hazy IPAs they lasted well into 4-5 weeks bottled and they were never cold crashed, which makes me think the cold crashing is part of the oxidation I'm seeing now and previously I just never connected the dots.

 

[doug293cz]

I wonder whether the amount of air that gets sucked back in is enough to cause significant oxidation.

Yes, given enough time.

I did some calculations a while back for a 24 liter (6.4 gal) fermenter with 20 liters (5.3 gal) of beer and 4 liters (1.1 gal) of headspace. At the end of fermentation, the headspace is 100% CO2 at an absolute pressure of 14.7 psi. If the fermentation temp was 18˚C (64.4˚F) and you cold crash to 1˚C (33.8˚F), then the CO2 partial pressure drops from 14.7 psi to 13.8 psi. Due to the drop in CO2 pressure, 0.9 psi worth of air will suck back into the headspace, and the headspace will then contain 0.9 / 14.7 = 6% air and 1.2% O2 (about 12,000 ppm O2.)

Now since you cooled the beer, it will absorb more CO2 from the headspace. When equilibrium is reached, the CO2 partial pressure in the headspace will be 8.0 psi, and enough more air needs to suck back to make the air partial pressure 14.7 - 8.0 = 6.7 psi. The percentage of air in the headspace will then be 6.7 / 14.7 = 45.6%, and the O2 percentage will be 9.6% (about 96,000 ppm.)

So, immediately after cold crashing you will have about 12,000 ppm O2 in the headspace, which is more than enough to oxidize the beer over time. As cold crashing continues, the O2 concentration will rise towards 96,000 ppm. And, as the O2 concentration rises, the rate of absorption of O2 into the beer will increase, allowing for even faster oxidation of the beer.

I don't have data on how fast O2 absorbs into the beer, nor how fast the actual beer oxidation occurs at cold crash temps. The only advice I can offer is to keep your cold crash time to the absolute minimum, and also minimize any agitation of the beer which could cause additional O2 absorption.

Brew on

 

[doug293cz]

duplicate

 

[murphyslaw]

Yes, given enough time.

I did some calculations a while back for a 24 liter (6.4 gal) fermenter with 20 liters (5.3 gal) of beer and 4 liters (1.1 gal) of headspace. At the end of fermentation, the headspace is 100% CO2 at an absolute pressure of 14.7 psi. If the fermentation temp was 18˚C (64.4˚F) and you cold crash to 1˚C (33.8˚F), then the CO2 partial pressure drops from 14.7 psi to 13.8 psi. Due to the drop in CO2 pressure, 0.9 psi worth of air will suck back into the headspace, and the headspace will then contain 0.9 / 14.7 = 6% air and 1.2% O2 (about 12,000 ppm O2.)

Now since you cooled the beer, it will absorb more CO2 from the headspace. When equilibrium is reached, the CO2 partial pressure in the headspace will be 8.0 psi, and enough more air needs to suck back to make the air partial pressure 14.7 - 8.0 = 6.7 psi. The percentage of air in the headspace will then be 6.7 / 14.7 = 45.6%, and the O2 percentage will be 9.6% (about 96,000 ppm.)

So, immediately after cold crashing you will have about 12,000 ppm O2 in the headspace, which is more than enough to oxidize the beer over time. As cold crashing continues, the O2 concentration will rise towards 96,000 ppm. And, as the O2 concentration rises, the rate of absorption of O2 into the beer will increase, allowing for even faster oxidation of the beer.

I don't have data on how fast O2 absorbs into the beer, nor how fast the actual beer oxidation occurs at cold crash temps. The only advice I can offer is to keep your cold crash time to the absolute minimum, and also minimize any agitation of the beer which could cause additional O2 absorption.

Brew on

Interesting, thanks.

Time seems to be the key. I usually cold crash for a day or two, then move to a purged keg.

 

[olotti]

Yes, given enough time.

I did some calculations a while back for a 24 liter (6.4 gal) fermenter with 20 liters (5.3 gal) of beer and 4 liters (1.1 gal) of headspace. At the end of fermentation, the headspace is 100% CO2 at an absolute pressure of 14.7 psi. If the fermentation temp was 18˚C (64.4˚F) and you cold crash to 1˚C (33.8˚F), then the CO2 partial pressure drops from 14.7 psi to 13.8 psi. Due to the drop in CO2 pressure, 0.9 psi worth of air will suck back into the headspace, and the headspace will then contain 0.9 / 14.7 = 6% air and 1.2% O2 (about 12,000 ppm O2.)

Now since you cooled the beer, it will absorb more CO2 from the headspace. When equilibrium is reached, the CO2 partial pressure in the headspace will be 8.0 psi, and enough more air needs to suck back to make the air partial pressure 14.7 - 8.0 = 6.7 psi. The percentage of air in the headspace will then be 6.7 / 14.7 = 45.6%, and the O2 percentage will be 9.6% (about 96,000 ppm.)

So, immediately after cold crashing you will have about 12,000 ppm O2 in the headspace, which is more than enough to oxidize the beer over time. As cold crashing continues, the O2 concentration will rise towards 96,000 ppm. And, as the O2 concentration rises, the rate of absorption of O2 into the beer will increase, allowing for even faster oxidation of the beer.

I don't have data on how fast O2 absorbs into the beer, nor how fast the actual beer oxidation occurs at cold crash temps. The only advice I can offer is to keep your cold crash time to the absolute minimum, and also minimize any agitation of the beer which could cause additional O2 absorption.

Brew on

Wow thanks Doug. I think this was the case with my latest dipa, I cold crashed it longer than I typically do so it achieved more suck back. The other dipa I bottled before that started showing signs at about 4 weeks buts that seems typical for my really hoppy IPAs and that was only cold crashed for about 24 hrs and now thinking back I avoided cold crashing some previous beers and those had an even longer shelf life but more sediment in the bottle, I think going forward I'll take that trade and may move to just using 22 oz bottles as those seem to last longer before any oxidation signs show up.

 

[55x11]

Wow thanks Doug. I think this was the case with my latest dipa, I cold crashed it longer than I typically do so it achieved more suck back. The other dipa I bottled before that started showing signs at about 4 weeks buts that seems typical for my really hoppy IPAs and that was only cold crashed for about 24 hrs and now thinking back I avoided cold crashing some previous beers and those had an even longer shelf life but more sediment in the bottle, I think going forward I'll take that trade and may move to just using 22 oz bottles as those seem to last longer before any oxidation signs show up.

Cold crashing longer just gives you longer exposure to oxygen, but the "suck back" only depends on the temperature. doug293cz gave a good rundown of physics involved.

I am still not convinced it's just cold crashing to blame for your oxidation problem.
I am not an expert on gas diffusion, but let's take forced carbonation as an example - it takes a long time, a week or so, to (deliberately) get CO2 from headspace to dissolve in a beer, at 1 atm, at very low temperatures.
In cold crashing, granted, we cannot tolerate even small fraction of oxygen, but we are not forcing it either, and there is still yeast to scavenge that oxygen.

How you bottle, in my opinion, has a lot more opportunities for splashing, which mixes oxygen much more rapidly than just sitting in the fridge, and assuming you don't flush every bottle headspace with CO2, that amount of air has a lot longer time of exposure to your bottled beer than 2 days of crashing.

Again, a lot of us (most of us) cold-crash for a day or two without any signs of oxidation.

 

[olotti]

Cold crashing longer just gives you longer exposure to oxygen, but the "suck back" only depends on the temperature. doug293cz gave a good rundown of physics involved.

I am still not convinced it's just cold crashing to blame for your oxidation problem.
I am not an expert on gas diffusion, but let's take forced carbonation as an example - it takes a long time, a week or so, to (deliberately) get CO2 from headspace to dissolve in a beer, at 1 atm, at very low temperatures.
In cold crashing, granted, we cannot tolerate even small fraction of oxygen, but we are not forcing it either, and there is still yeast to scavenge that oxygen.

How you bottle, in my opinion, has a lot more opportunities for splashing, which mixes oxygen much more rapidly than just sitting in the fridge, and assuming you don't flush every bottle headspace with CO2, that amount of air has a lot longer time of exposure to your bottled beer than 2 days of crashing.

Again, a lot of us (most of us) cold-crash for a day or two without any signs of oxidation.

Oh I'm sure there's something going on with my bottling process. It was mentioned to me that maybe not capping right away could be part of the prob as I'll fill a case of bottles then I'll cap them then do another case and cap when I should try literally be filling one and capping it right away. I use the wand that attaches to the bucket spigot so I just depress it and fill until a little flows over and set it aside then do the next.

 

[doug293cz]

Oh I'm sure there's something going on with my bottling process. It was mentioned to me that maybe not capping right away could be part of the prob as I'll fill a case of bottles then I'll cap them then do another case and cap when I should try literally be filling one and capping it right away. I use the wand that attaches to the bucket spigot so I just depress it and fill until a little flows over and set it aside then do the next.

+1 to capping immediately after filling, rather than filling a bunch and then capping.

Brew on

 

[olotti]

+1 to capping immediately after filling, rather than filling a bunch and then capping.

Brew on

I hope the fix is really this easy.

 

[khillian]

I never had fresh commercial quality IPA until I switched to kegging. Oxidation is the blame for lots of bland meh homebrew. After reading the purging thread on here when kegging I now purge 30PSI 7 times after filling my keg. I have taken cold crashing primary out of my process as beers clear in the keg over 7-10 days. I don't mind cloudy beers anyway. Lately my hoppy beers don't last more then 3 weeks but the aroma/flavor is commercial quality the whole time.

 

[jappler]

Now you guys got me worried. My beers been cold crashing for a little over 2 days now. I'll be running home to transfer it to the keg

 

[Bilbo1usa]

I haven't seen this mentioned, so I thought I'd share my technique.
I'm not claiming it's better or worse, but it seems to work for me.

When I begin my cold crash, I remove the airlock entirely, covering the top of the carboy (still with the stopper) with some sanitized aluminum foil.
I squeeze the foil tightly and use a rubberband to secure it.

I crash to 32*...usually takes a couple of days to get that cold.
The foil gets sucked pretty tight at this point, but not remarkably so.
Note: I use plastic carboys, so that might account for some flex as the negative pressure builds. Glass carboy might require a little pocket or space under the foil at the top?

Then I pull the chilled carboy out and let it warm back up a bit while I prepare my kegging/bottling equipment. (maybe an hour?)
It doesn't warm back up too much in that time, maybe a couple of degrees, but it seems to be enough to relax some of the pressure in the carboy and on the foil.

I then keg or bottle as normal.
The beer tends to taste pretty good.

Good brewing!
Bill

 

[murphyslaw]

I doubted the significance of this issue until I attended a homebrewcon seminar last week about oxidation. Now I"m really paranoid about oxidation.

I normally cold crash in primary, but last night I transferred to a fully purged keg (displaced sanitizer) and began my cold crash in there. Now I"m all worried about how to avoid oxidation on the bucket side of the transfer and when I open to the keg to add gelatin/dry hops.

 

[Northbank]

However did all those gabillions of people brew beer for centuries without positive pressure equipment and a lab?

 

[murphyslaw]

However did all those gabillions of people brew beer for centuries without positive pressure equipment and a lab?

Less well.

 

[freisste]

Less well.

+1.

"Good enough" and "best we can do" is not necessarily "optimal"