Cold crash and oxidation

[marchio-93]

mediant says his fermenter draws back up to 1.5 litres? That seems like quite a bit when on average headspace is normally 4-5 litres. Also, cold crashing is a slow event, like others have said the "bubbles" of sucking back air happen slowly while the beer is cooling from your ferm temp to whatever you are crashing to.

And I add, I think it would be difficult to not hear 1.5 litres trough a 30 cc airlock

 

[yoop89]

If you would like to visually monitor how much suckback you get during cold crash you could buy or build something like this. Hook it up for fermentation and watch how much sanitizer/co2 is pulled back.

https://www.norcalbrewingsolutions.com/store/CO2-Carbon-Dioxide-Harvester-Kit.html

I was considering something like this but just stopped cold crashing.

 

[McKnuckle]

...the only reason I don't hear or see any bubble is because the amount of O2 gone through the airlock is very little, and so I can not hear it. The amount of Co2 that get out during fermentation is not very huge, but you hear that sound for days.

Actually the amount of CO2 leaving during fermentation is pretty large (gallons worth), and it's pressurized with respect to the atmosphere around it. So the force of leaving the bucket through the airlock causes obvious bubbling.

In contrast, the amount of air entering during cold crash is only enough to fill the head space at atmospheric pressure, and it is probably drawn in slowly (I'll correct my post above), which is why it's not as easy to see.

I haven't cold crashed with an airlock in a long time, but when I did, I never saw the ingress of air, BUT I could tell that it happened, because the airlock liquid became visibly depleted.

 

[marchio-93]

If you would like to visually monitor how much suckback you get during cold crash you could buy or build something like this. Hook it up for fermentation and watch how much sanitizer/co2 is pulled back.

https://www.norcalbrewingsolutions.com/store/CO2-Carbon-Dioxide-Harvester-Kit.html

I was considering something like this but just stopped cold crashing.

Thanks! I think I'll start with a balloon and watch what happen

 

[yoop89]

And I add, I think it would be difficult to not hear 1.5 litres trough a 30 cc airlock

Are you inside the fermenter? The noise of a bubble is caused on the surface of the liquid it is breaking. When drawing air back in that surface is now inside a bucket insulating it ever so slightly. I guarantee it bubbled albeit very slowly so possible you just didnt "catch" one?

 

[RPh_Guy]

Sorry double post

 

[RPh_Guy]

Here is a link to anyone who wants to see for themself how gases mix.

It says exactly that if a gas it's heavier than another it takes a lot of time to mix

In the clip, the Br2 and "air" is fully mixed after just half an hour. Br2 is about 4 times as heavy as C02.

It was implied here that CO2 diffusion is faster because Graham's Law states that the diffusion rate is inversely proportional to the square root of the mass of the molecule. Also notice that the mixing starts immediately and the initial rate of mixing near the interface is (exponentially) higher because of the higher concentration gradient.
The physics of gas movement is well understood.

Of further interest, during a cold crash two processes are occurring:
1. Thermal contraction of the liquid and gas in the headspace. This is more than enough to pull in too much oxygen in its own right, and the amount of air pulled in can be easily calculated using the ideal gas law.
2. The solubility of carbon dioxide increases, so a lot of the gas in the headspace gets absorbed into the beer. This process pulls in the majority of the outside air.

It's a scientific fact that air is being pulled into a fermenter when the temperature drops significantly, when there is only a fluid-filled airlock.

I can not hear people say "you completely wrong" or things like that, to other people, as they have the truth in their hand, when their is nothing more approximate than our hobby. Maybe to justify thousands of dollars' worth of equipment, and then repeat the same sentence without giving a real scientific answer

I know you're not referring to me because the first thing I suggested was spunding instead of cold crashing.
Spunding is the ultimate way to reduce cold side oxidation.

Please be respectful when people are putting out information to help answer your questions. We are all trying to help.

 

[mkopec1]

What do you mean by spunding instead of cold crashing? Dont do cold crashing? Im not sure I understand.

 

[marchio-93]

In the video there is a small amount of gas, I had 10 litres of Co2 in my fermenter, so cold crashing in some days, not in one minute, I think my headspace is not full of 02 in few seconds as you said.

The only one who did not respect other people opinions was you, because you did not just put some notions in those posts, but you said other people were completely wrong and saying cold crash 02 would STRONGLY affect the beer, so I repeat to you maybe email the judges of the Belgian IPA, heavely hopped, and say them to change their hobby/job

 

[RPh_Guy]

What do you mean by spunding instead of cold crashing? Dont do cold crashing? Im not sure I understand.

Yes, that is what I'm recommending.
Actively fermenting yeast protect beer from oxidation by rapidly absorbing any dissolved oxygen.
The longer the beer sits after fermentation ends, the more oxygen exposure occurs.

In the video there is a small amount of gas, I had 10 litres of Co2 in my fermenter, so cold crashing in some days, not in one minute, I think my headspace is not full of 02 in few seconds as you said.

Mixing of gases occurs fast enough that there is no such thing as a CO2 blanket, even during active fermentation. This is based on the science of gas physics.

Air is drawn into your fermenter over a period of hours-days. The headspace mixes relatively rapidly. Oxygen in the headspace forms an equilibrium with some of it dissolving in the beer. Oxygen radical species from dissolved oxygen are what causes the "oxidation" changes in flavors. Since the dissolved oxygen is consumed by these reactions, Le Chatelier's principle dictates that even more oxygen will dissolve into the beer to maintain equilibrium.

The only one who did not respect other people opinions was you, because you did not just put some notions in those posts, but you said other people were completely wrong and saying cold crash 02 would STRONGLY affect the beer, so I repeat to you maybe email the judges of the Belgian IPA, heavely hopped, and say them to change their hobby/job

This is what I said:

To my taste, yes, strongly.

I chose my words carefully since everyone has different tastes.

 

[Robert65]

It seems to me that the exact amount of oxygen drawn into the headspace (and ultimately dissolved in the beer) during a conventional cold crash is unimportant. Whatever the amount, it will be measured in percent, parts per hundred. Meanwhile, the maximum tolerable amount of oxygen exposure for beer after active fermentation has abated, to avoid noticeable, damaging oxidation, is measured in parts per billion. So it is advisable to do whatever we can to avoid oxygen ingress.

Spunding really is the ultimate solution for homebrewers. This means transferring the beer from the fermenter to the keg -- a closed transfer to avoid as much risk as possible -- when there is still just enough fermentation left to go to naturally carbonate the beer. The benefits include that active fermentation will scavenge the small amount of oxygen inevitably picked up even in a closed transfer, and you will have fully carbonated beer by the time it reaches FG without the need for force carbonation with gas that costs good money (and is not nearly as pure as fermentation generated CO2.) Then you can cold crash the keg to clear the beer for serving. This also obviously greatly reduces turnaround time for the batch.

 

[marchio-93]

This is what I said:

I chose my words carefully since everyone has different tastes.

You don't know the kind of beer, how long I've cold crashed but you know it will strongly affected by oxidation. Okay. When, apart from the long-term loss of characteristics (and my beers are mostly finished in two months) you cannot describe it in any other way. Great

 

[marchio-93]

, and you will have fully carbonated beer by the time it reaches FG without the need for force carbonation with gas that costs good money (and is not nearly as pure as fermentation generated CO2.)

Thanks! But I don't get this part. Do you calculate the carbonation you get in your beer by the eaten point of gravity?

And do you dry hop directly in your keg?

 

[Robert65]

Thanks! But I don't get this part. Do you calculate the carbonation you get in your beer by the eaten point of gravity?

There are other threads on the forum going into much more detail on spunding. But in short:

You will want to have an idea of what the final gravity of your beer will be. The best way to determine this is a forced fermentation test (FFT,) but experience may be a guide.

Then you may want to account for the amount of CO2 dissolved in beer depending on temperature: a cold fermented lager will have more than a warm fermented ale.

You will then transfer the beer at 0.5-1°P or 0.002-0.004 specific gravity above final.

Finally, most people use a spunding valve, a variable pressure relief valve with a pressure gauge to monitor pressure, to make sure any excess is vented, setting the pressure based on the usual charts showing volumes of CO2 against temperature and pressure.

It is also possible to apply the principle in bottling, but that requires greater precision since you'll have no relief valve, and it's not something I have done myself.

 

[RPh_Guy]

Oxidation affects all beers because all beers contain compounds that will react with dissolved oxygen.
These reactions occur over days to weeks at typical temperatures at which beer is stored.

While different styles of beer can respond differently, oxidation generally results in the muting of desirable hop and malt characteristics, creates a more harsh bitterness, caramel notes, catty and grassy notes from hops, and at some point papery/cardboard flavors. It's a complex process, so any answer in a forum post is going to be an over-simplification. I personally don't like the effects of oxidation and taste them quite readily.

Ultimately what matters is whether you're happy with your beer.
The science of these chemical reactions and physical processes is factual and unbiased. However what you choose to do with the information is up to you and your tastes and brewing goals.

Cheers

 

[marchio-93]

Ultimately what matters is whether you're happy with your beer.

Of course.
And if you can taste too caramel or harshness and say it comes from O2 and not from ph, dry hopping, and other billions of reasons then congrats!

 

[mkopec1]

There are other threads on the forum going into much more detail on spunding. But in short:

You will want to have an idea of what the final gravity of your beer will be. The best way to determine this is a forced fermentation test (FFT,) but experience may be a guide.

Then you may want to account for the amount of CO2 dissolved in beer depending on temperature: a cold fermented lager will have more than a warm fermented ale.

You will then transfer the beer at 0.5-1°P or 0.002-0.004 specific gravity above final.

Finally, most people use a spunding valve, a variable pressure relief valve with a pressure gauge to monitor pressure, to make sure any excess is vented, setting the pressure based on the usual charts showing volumes of CO2 against temperature and pressure.

It is also possible to apply the principle in bottling, but that requires greater precision since you'll have no relief valve, and it's not something I have done myself.

I see now, but with a fully closed system like you propose, how do you test gravity before you rack into keg? It would seem that any test like this would inevitably introduce O2.

 

[lump42]

Okay thanks I've seen the video now. But what about a plastic bucket?

The easiest procedure would be to install a spigot on the bottom and attach the keg gas post back to the airlock. While the keg fills with beer, the CO2 from the keg is pushed out the gas post, which has tubing connected to the airlock stem on the bucket lid. The bucket headspace fills with CO2 from the keg as the beer level drops. The beer fermentor and the co2 in the keg swap places.

It would be similar to this video but with a plastic bucket and a spigot.

 

[Robert65]

I see now, but with a fully closed system like you propose, how do you test gravity before you rack into keg? It would seem that any test like this would inevitably introduce O2.

I ferment in a pressure capable fermenter (a modified 10 gallon corny.) So I just put gas on the in port and use a picnic tap to take a sample from my floating dip tube. (I also have a spear tube for pulling slurry, but that's another story...) Something like this can be improvised with most fermenters, as long as you can put gas in to replace the volume coming out. You obviously have to be able to do this to do a closed transfer anyway, so it should already be arranged.

 

[RPh_Guy]

I see now, but with a fully closed system like you propose, how do you test gravity before you rack into keg?

In any fermentation vessel with a spigot you can drain out beer slowly while keeping an eye on the airlock. CO2 production from active fermentation continually replaces the beer being drained, so no air will be pulled in if you're careful. Make sure the airlock is full so there's some leeway.
Same goes if using a blow-off tube; keep an eye on the solution in the blow-off container (or tubing if you're using something see-though).

Using a refractometer instead of a hydrometer to compare it to the FFT reduces the amount of beer you need to sample for monitoring purposes.

 

[303Dan]

This sentence has been repeated a lot of time, and referring to something that is not incorrect at all. As someone said I pick up several litres of O2 but can not answer to the question "why not a single bubble in the airlock".

I don't know if this is even the most relevant question in this thread to answer at this point, but I don't think anyone has answered it yet in this way:

If I understand you correctly that you have cold crashed and not observed any suck back at all in any way, then the only conclusion I can make is that there is another point of ingress to your fermenter other than your airlock. That's the only alternate scenario in my mind given what you've said. You can't take a closed container, drop the temperature inside of it by 30-40 degrees F and not have the internal pressure drop. At that point, either the container is truly air-tight and structurally able to withstand the pressure, or one of the following things happens: either the container is truly air-tight and closed and NOT structurally capable of handling the conditions and it collapses. Or the container is truly air-tight and closed and IS structurally capable of handling the conditions, or it is not truly air-tight and the pressure will equalize with the outside atmosphere. In the case of a plastic fermenter like yours, it has to equalize. So, if there is only one point of ingress and that is your airlock, there absolutely, positively HAS to be suck-back. If there is no suck-back through the airlock, then the air is finding an easier/alternative path in.

This, in no way, addresses the topic of oxidation and how much that affects your beer. Just trying to lend an explanation for why you may not have witnessed evidence of suck back through your airlock.

 

[Broothru]

I don't know if this is even the most relevant question in this thread to answer at this point, but I don't think anyone has answered it yet in this way:

If I understand you correctly that you have cold crashed and not observed any suck back at all in any way, then the only conclusion I can make is that there is another point of ingress to your fermenter other than your airlock. That's the only alternate scenario in my mind given what you've said. You can't take a closed container, drop the temperature inside of it by 30-40 degrees F and not have the internal pressure drop. At that point, either the container is truly air-tight and structurally able to withstand the pressure, or one of the following things happens: either the container is truly air-tight and closed and NOT structurally capable of handling the conditions and it collapses. Or the container is truly air-tight and closed and IS structurally capable of handling the conditions, or it is not truly air-tight and the pressure will equalize with the outside atmosphere. In the case of a plastic fermenter like yours, it has to equalize. So, if there is only one point of ingress and that is your airlock, there absolutely, positively HAS to be suck-back. If there is no suck-back through the airlock, then the air is finding an easier/alternative path in.

This, in no way, addresses the topic of oxidation and how much that affects your beer. Just trying to lend an explanation for why you may not have witnessed evidence of suck back through your airlock.

Just to tag on and add another observation: I'm currently brewing a lager in a unitank. There's around 5.25 gallons in the fermenter which has a 7 gallon capacity plus headspace of about an additional 1.5 gallons, so let's say roughly 8.5 gal holding 5.25 gal, or roughly 3.25 gallons of gaseous volume in the headspace.

When fermentation was within 5 pts. SG (determined by FFT) it was "capped" with a spunding valve set to 15 psig. The beer continued to ferment to completion at 50F, absorbing the generated CO2. After a few days at stabilized 15 psig and 50F, the temperature was lowered to 38F. After 3 days at 38F the pressure had fallen to 12.5 psig.

So, if someone wants to do the math, how much was the gaseous volume (~3.25 gal) 'reduced' when the 15 psi @ 50F CO2 in the headspace became 12.5 psi @ 38F. Or stated another way, how much ambient air (20% O2/80% N) would have been drawn into the 3.25 gal. volume headspace at ambient temperature and pressure with a temperature drop of 12F?

Solve:

Brooo Brother
(aka: the guy who no longer does 'math in public').

 

[RPh_Guy]

how much ambient air (20% O2/80% N) would have been drawn into the 3.25 gal. volume headspace at ambient temperature and pressure with a temperature drop of 12F?

None because you still have positive pressure in the tank

 

[bob1852]

Solve:

Brooo Brother
(aka: the guy who no longer does 'math in public').

Several have done the calculations in the dozens of other threads on the topic. The answer is out there....(unfortunately the search function on HBT has always been a little suspect...especially on mobile).

 

[Broothru]

Several have done the calculations in the dozens of other threads on the topic. The answer is out there....(unfortunately the search function on HBT has always been a little suspect...especially on mobile).

Yeah, I was thinking that I could use the Forced Carb tables to determine approximate volumes at specific temps and pressures and then compare the values at 38F/12.5 psig with 50F/15 psig. Then apply that to 3.25 gallons of headspace volume at ambient room temp and pressure. That is apples to oranges of course (unpressurized gaseous volume to pressurized dissolved volumes of gas in a liquid). Then my head started hurting, so I quit.

Intuitively I think it might be about 2.6 liters of O2 (~3.25 gal • 4 l/gal • 20%) getting sucked into the fermenter.

Don't ask to see my work. It's ugly, and quite likely wrong.

Brooo Brother

 

[Broothru]

None because you still have positive pressure in the tank

Naw, I meant to say 'whatif' I had an an airlock on the fermenter at ambient temperature/pressure and then crashed to 38F unpressurized, how much volume of gaseous O2 would get sucked into the headspace.

The LoDO gurus say it doesn't take much, as little as a few ml of O2 to get a foothold and start affecting your beer. I'm guessing the volume of contaminating air would be a couple thousand times that amount but can't do the proof.

Brooo Brother

 

[RPh_Guy]

That is apples to oranges

^ This was my point. Your pressure change data won't apply to a fermenter that's non-pressurized, so the hypothetical doesn't make sense.

If you want to do the math (for a non-pressurized system), the ideal gas law alone will take care of the thermal contraction and then you'll need to figure out the change in CO2 solubility to see what volume of the headspace would dissolve.
This should help:
https://www.homebrewtalk.com/forum/...-from-blowoff-tube.646327/page-2#post-8422519

 

[Broothru]

^ This was my point. Your pressure change data won't apply to a fermenter that's non-pressurized, so the hypothetical doesn't make sense.

If you want to do the math (for a non-pressurized system), the ideal gas law alone will take care of the thermal contraction and then you'll need to figure out the change in CO2 solubility to see what volume of the headspace would dissolve.
This should help:
https://www.homebrewtalk.com/forum/...-from-blowoff-tube.646327/page-2#post-8422519

《Insert "Aha!" moment...》

I think I'm starting to see the light. Thanks.

Brooo Brother

 

[day_trippr]

Holy cow, I'm surprised there could be so much discussion about a known problem with plenty of solid countermeasures already extant.
Y'all just bored or what?

Cheers!

 

[marchio-93]

Yes, that is what I'm recommending.
Actively fermenting yeast protect beer from oxidation by rapidly absorbing any dissolved oxygen.
The longer the beer sits after fermentation ends, the more oxygen exposure occurs.

Hello! I have another question, if the airlock does not perfectly hold the pressure, and has some vents at the base, on the first / second day of fermentation, is there a risk of oxidation? I noticed it late and only changed the airlock now