Cold crash and oxidation

[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.

 

[Brooothru]

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).

 

[Brooothru]

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

 

[Brooothru]

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

 

[Brooothru]

^ 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

 

[RPh_Guy]

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

Actively fermenting yeast protect beer from oxygen pretty well, so that shouldn't be a problem.

 

[marchio-93]

Actively fermenting yeast protect beer from oxygen pretty well, so that shouldn't be a problem.

Thanks!

 

[cicquetto]

I bought the cap for my SS brewbucket. can I proceed with the cold crash without problems?

https://www.ssbrewtech.com/collections/accessories/products/1-5-tc-cap

 

[Brooothru]

I bought the cap for my SS brewbucket. can I proceed with the cold crash without problems?

https://www.ssbrewtech.com/collections/accessories/products/1-5-tc-cap

NO!!!

The lid will seal the tank. Then when you chill, the volume of air will contract, creating a vacuum. The vacuum will cause stresses on the lid, sides and latches of the Brew Bucket that could cause it to implode (not explode) and collapse into itself. The Brew Bucket should not be PRESSURIZED above 2 psig (positive pressure). It should never be subjected to VACUUM (negative pressure) or it could be crushed from within. Almost any tank will hold at least some positive pressure, but nearly all tanks are susceptible to failure from very small vacuums (negative pressure).

Brooo Brother

 

[Cevan65]

NO!!!

The lid will seal the tank. Then when you chill, the volume of air will contract, creating a vacuum. The vacuum will cause stresses on the lid, sides and latches of the Brew Bucket that could cause it to implode (not explode) and collapse into itself. The Brew Bucket should not be PRESSURIZED above 2 psig (positive pressure). It should never be subjected to VACUUM (negative pressure) or it could be crushed from within. Almost any tank will hold at least some positive pressure, but nearly all tanks are susceptible to failure from very small vacuums (negative pressure).

Brooo Brother

I brew in 4 gal Anvil fermenters. I simply plug the hole in the lid and cold crash for two days. Have done this at least 20 times with two different fermenters and no issues.

 

[Brooothru]

One of several possibilities:

1). You have a large liquid volume and little or no headspace; or,

2). You have an air leak around the 'plug' that allows the negative vacuum pressure to equalize; or,

3). The temperature delta between your beer's starting temperature and the crashed temperature is not that great to create a significant negative pressure vacuum; or,

4). You have an undiscovered breach of your Anvil's lid seal gasket that allows the tank to equalize; or,

5). The smaller size of a 4 gallon bucket affords greater rigidity, thus resistance to deformation, than a 7 or 14 gallon Brew Bucket; or,

6). Good luck and fortune have gotten you this far without destroying your gear. Consider it borrowed time; or,

7). One or more of the above


There's one other possible explanation, but you'd have to exist in an alternative reality where the physical laws of the universe don't.

Somewhere in my archives of aviation blunders I have pictures of a 6,000 gallon fuel truck that imploded while defueling an airplane when the truck's negative pressure relief valve wasn't opened by the refueler. In another instance the wing of a B-52 was sucked in, crushed and broke away from the fuselage, totally destroying the airplane, when the automatic wing tank vent failed to open when it was being defueled. So, scratch one steel tanker truck and one multi-million dollar bomber due to separate accidents caused by negative pressure (vacuum). I can guarantee you that both the truck and the B-52 were a lot more sturdy than your Anvils are.

Brooo Brother

 

[Cevan65]

My 4 gallon fermenter has 3 gallons of beer and 1 gallon of headspace. When I pull the plug, it is obvious that air is rushing in, so I don’t think there is any air leakage.

The temp during cold crash goes from 68 to 38 degrees. Assuming the headspace is at 14.7 psi just prior to cold crashing, my calculations show the psi of the headspace going down to 13.6 psi. I am using .0584 liters as the amount of reduction of beer volume and thus the increase in headspace volume.

So is a less than 1 psi reduction in the headspace pressure enough to damage my fermenter? I don’t think so. The first thing that would happen is the plug would get sucked into the fermenter as it is rubber.

 

[InvertedPilot]

Ebay can be your best friend. I am crashing 100 gallons in a custom fermentor. This particular blanketing regulator is capable of 7-10 WC (Water closet) which is 0.25 to 0.36 PSI. Any overpressure is vented. During crash there is no chance of blow off. Unfortunately I started cold crash with the vent line in a beaker with star san . It sucked it about 2 cups light star san solution but at least it was not oxygen. 2 cups of diluted star san are probably going to have minimal impact on taste of 100 gallons. The total amount of star san was less than a 1/4 oz in the 2 cups that were sucked back.

 

[InvertedPilot]

An alternative is the $14.00 PLAATO suck back protector. You can blow some CO2 into a mylar balloon and attach to the inlet of the suckback protector that way any suck back will be only CO2. Below is the Plaato suckback protector. It just goes inline with the fermenter bung and existing airlock. Attach a mylar balloon with co2 to the side with a rubber band and your done. Total cost under $20.

 

[day_trippr]

That's twice what I paid for my BBQ regulator...