Positive pressure cold crash

[Anyhowe]

Hey brainiacs. I ferment 2.5 gallon batches in 5 gal corny kegs. Plenty of headroom. Before I cold crash I was going to remove the airlock and replace it with the corny lid and purge with co2, then again add co2 to pressurize the tank to reduce any vacuum during the crash. Any ideas on how much pressure to use? Thanks.

 

[kombat]

I just set mine to the usual 12-15 psi and leave it hooked up. Carbonate while cold-crashing/clearing.

 

[Anyhowe]

Not sure I want to rack carbonated beer. I just wonder how much pressure I would have to add to be close to neutral after the cold crash.

 

[k1ngl1ves]

Whatever pressure, it's still going to be absorbed. Why not just hook it up at under 5 pounds? That should be low enough...

 

[Anyhowe]

Whatever pressure, it's still going to be absorbed. Why not just hook it up at under 5 pounds? That should be low enough...

Good point, maybe 5 psi of beer gas as the N would not be absorbed.

 

[k1ngl1ves]

Good point, maybe 5 psi of beer gas as the N would not be absorbed.

Sure. You could waste nitro if you wanted. Or just put more than 1 pound of co2 on it and no worries. Actually, if you were confident in your keg seal, you could start by purging then hitting it with 20 #'s of co2 and disconnecting, cold crashing, and end up a bit negative... and still be ok.

I think you're really over thinking this, and I have terribad OCD. So you're probably really really over thinking this...

 

[Anyhowe]

Sure. You could waste nitro if you wanted. Or just put more than 1 pound of co2 on it and no worries. Actually, if you were confident in your keg seal, you could start by purging then hitting it with 20 #'s of co2 and disconnecting, cold crashing, and end up a bit negative... and still be ok.

I think you're really over thinking this, and I have terribad OCD. So you're probably really really over thinking this...

Quite the opposite. I am really not thinking much about it, that is why I asked here and didn't spend the time to figure it out myself. I am sure that one (with scientific tendancies like those water gurus on that other thread) could actually Calculate the reduction due to cooling.

You say 20 psi, I assume that was just a wag or have you done it? I was just curious because it is likely fine to do nothing and just have some negative pressure in the corny. But I thought that it might be cool to try to find the balance point.

 

[masonsjax]

A corny won't hold a vacuum. What problem are you trying to solve here? Do you feel there would be a negative impact to cold crashing at atmospheric pressure? Are you bottling? If serving from a keg, why not just carb it and serve it in the corny you're crashing in?

 

[Anyhowe]

A corny won't hold a vacuum. What problem are you trying to solve here? Do you feel there would be a negative impact to cold crashing at atmospheric pressure? Are you bottling? If serving from a keg, why not just carb it and serve it in the corny you're crashing in?

I usually crash in the fermentation cornet then rack to a conditioning/serving corny. Just trying to keep o2 out of the beer when crashing

 

[masonsjax]

There's really no need to rack it again, just go ahead and serve from the same keg you're crashing in. My opinion anyway.

 

[k1ngl1ves]

There's really no need to rack it again, just go ahead and serve from the same keg you're crashing in. My opinion anyway.

He ferments in the corney keg. He wants to crash that keg, then siphon the beer off the trub into another keg after crashing.

I think people are missing that part. The initial keg is full of trub.

 

[IslandLizard]

@OP
Since there's a decent size head space in those kegs (2.5 gallon) there's also a decent amount of CO2 in it, even at modest pressures. Don't compare this to a full keg with only a quart of headspace. You only need to compensate for the contraction of the 2.5 gallon of liquid, and what is being absorbed by the beer during your cold crash to retain a high enough positive pressure to maintain the seal. And even if the seal gets lost, I doubt there is much air seeping in around the lid.

 

[masonsjax]

Ahh right, he's fermenting in them.

Yes the amount of CO2 in the headspace would be plenty protection against oxidation while crashing. I wouldn't pressurize at all, or even seal the lid. Actually, I'd keg it first, then crash and carb in one shot, which is exactly what I do except that I ferment in carboys or sanke kegs.

 

[rnm410]

I can run these calcs if you are still interested.

 

[Anyhowe]

I can run these calcs if you are still interested.

Yes! Thank you.

I would prefer to crash and use gelatin in the primary before transfer to the conditioning and serving keg. It would be great to know roughly what pressure I should add after to fermentation is complete such that I am close to equal after the crash.

Again, thank you.

 

[rnm410]

Yes! Thank you.

I would prefer to crash and use gelatin in the primary before transfer to the conditioning and serving keg. It would be great to know roughly what pressure I should add after to fermentation is complete such that I am close to equal after the crash.

Again, thank you.

For the case from 60*F to 40*F

Specific volume change of the liquid is in the hundredths of thousandths difference, i.e. vacuum formed do to liquid contraction is negligible.

The negative pressure relative to outside the keg due to cooling of the gas in the head space is -0.6 psi.

This calculation neglects the amount of new gas entering, which is about the volume contained in a 12 oz can. And also neglects how much gas from positive pressure will be absorbed by the liquid.

Can you post a picture of your setup?

I may have a solution for you.

 

[Anyhowe]

For the case from 60*F to 40*F

Specific volume change of the liquid is in the hundredths of thousandths difference, i.e. vacuum formed do to liquid contraction is negligible.

The negative pressure relative to outside the keg due to cooling of the gas in the head space is -0.6 psi.

This calculation neglects the amount of new gas entering, which is about the volume contained in a 12 oz can. And also neglects how much gas from positive pressure will be absorbed by the liquid.

Can you post a picture of your setup?

I may have a solution for you.

Well there is really no picture to be had or taken. Simply a 5 gal corney keg wth 2.5 gallons of beer in it sitting in the fridge. I was gong to put in the lid and shoot it with x psi to get a positive charge then remove the gas. The idea was to balance the contraction due to cooling to end up relatively neutral after the crash.

 

[rnm410]

Well there is really no picture to be had or taken. Simply a 5 gal corney keg wth 2.5 gallons of beer in it sitting in the fridge. I was gong to put in the lid and shoot it with x psi to get a positive charge then remove the gas. The idea was to balance the contraction due to cooling to end up relatively neutral after the crash.

Achieve and maintain minimal positive pressure, therein lies your answer. I believe the minimum ours regs can supply is about 2psi. This will have no negative effect on yeast health, possible small amounts of carbonation will form.

Possibly flush and pressure the keg prior to transferring to seat the orings.

 

[tagillis]

Ahh right, he's fermenting in them.

Yes the amount of CO2 in the headspace would be plenty protection against oxidation while crashing.

Hey masonsjax, Would you mind expanding upon this? At what point are you at risk of oxidation, i.e. - what if there was only had 1.5 gallons of head space? I've recently heard some conflicting schools of thought on cold crashing induced oxidation. Just trying to gather more info and perspectives.

 

[rnm410]

Maybe this will have some value here. https://www.homebrewtalk.com/showthread.php?t=44344

 

[masonsjax]

If there's co2 in there it is heavier than air and should settle on the surface creating a protective layer. If you're not actively splashing the beer around, you should be fine. I've had beers sit in primary for a year in a PET carboy at room temp and taste perfectly fine. A few weeks cold crashing in a sealed keg is nothing to worry about IME.

 

[Anyhowe]

Fwiw my main concern has nothing to do with oxygenation or carbonation for that matter. It is just a matter of science wondering how much positive pressure one needs in my situation such that the reduction in pressure due to the contraction caused by cooling is accounted for.

 

[rnm410]

Fwiw my main concern has nothing to do with oxygenation or carbonation for that matter. It is just a matter of science wondering how much positive pressure one needs in my situation such that the reduction in pressure due to the contraction caused by cooling is accounted for.

Already stated 0.6 psi. Which equates to a draw of about 12 oz of gas volumetrically.

 

[day_trippr]

Warning: there are allegedly sentient beings that still believe in CO2 blankets.

That is all.

Cheers!

 

[IslandLizard]

Warning: there are allegedly sentient beings that still believe in CO2 blankets.

That is all.

Cheers!

I for one believe in CO2 blankets, use them all the time. They just don't exist with another gas present in the same space.

 

[kombat]

Achieve and maintain minimal positive pressure, therein lies your answer. I believe the minimum ours regs can supply is about 2psi. This will have no negative effect on yeast health, possible small amounts of carbonation will form.

Be careful with this. With most of my kegs, they'll leak with such low pressures. Most of mine need to be pressurized to at least 5-8 psi to seal completely, otherwise they'd slowly leak out all your CO2. What I'm trying to say is, unless you've got a tightly-sealed keg, I don't think it's possible/practical to try and keep it pressurized at 2 psi without losing a lot of CO2 in the process.

 

[Anyhowe]

Already stated 0.6 psi. Which equates to a draw of about 12 oz of gas volumetrically.

Interesting. Given that 1 psi equates to about 2.3 feet of 'head' elevation, how is it that people are sucking quantities of starsan into their carboys through a blowoff tube during the crash? .6 psi could only raise the starsan about a foot or 1/2 the height of the carboy.

 

[kombat]

Interesting. Given that 1 psi equates to about 2.3 feet of 'head' elevation, how is it that people are sucking quantities of starsan into their carboys through a blowoff tube during the crash? .6 psi could only raise the starsan about a foot or 1/2 the height of the carboy.

Keep in mind that the liquid is contracting too, creating an additional suction effect.

 

[Anyhowe]

Keep in mind that the liquid is contracting too, creating an additional suction effect.

Ok now I am starting to think about it... But only a little. The density of water at 70 degrees is roughly 0.998 At roughly 40 degrees it is 1.0. (An insignificant difference?) As it cools below 40 degrees it actually begins to become less dense and as you all know expands on its way to freezing at about .934 or 9% less dense than room temperature water. So I have doubts about the above comment.

Likely then the most significant contraction amount is possibly due to the absorption of the gas into the liquid?

 

[k1ngl1ves]

Wow. This is really going down the rabbit hole now...