Does an oil filled pressure gauge read correctly at 33 degrees Fahrenheit?

[iandanielursino]

On Sunday I set the temperature on my freezer based fermentation chamber to 33 F from 80 F. After one night the pressure gauge on my conical was reading 8.5 PSI, now after two nights it's reading 5.5 PSI.

I'm worried it's leaking but also, do pressure gauges even work at 33 F?

It's actually a fruit wine in there, but this is a test run for lagering. I needed to get the fermenter filled quick because my warranty on my tank and PRV are expiring soon.

I did pour a sample yesterday and forgot to check the gauge after. Would one glass dump the pressure inside?

 

[Broken Crow]

Sounds like it's just a bit slow to chill...pressure always drops as it gets colder.. just read the carb-chart diagonally;

 

[iandanielursino]

The temp probe is just in a well in the front of the tank so I think the wine had already gotten to 33 when it was 8.5 PSI. But yeah I suppose I would expect that for 2 or 3 weeks it will continue to gradually lose pressure as the carbon dioxide enters the fluid until it reaches equilibrium, I wasn't expecting it to be so drastic but maybe that is naïve. Starting to think with a 15 PSI system I may not be able to carb while lagering purely from spund, but that's fine I can just add some CO2 during the lagering process to keep it at the target pressure.

This is a pretty extreme test though I went all the way from 80 to 33, usually it would be like 68 for a diactyl rest down to 33.

Looking at a chart that actually goes up to 80, https://cdn.homebrewtalk.com/images/1/0/2/7/4/6/preschart1-68415.jpg there was only about 1.42 vol before the crash. I'm not sure what that means really, neither pressure nor volumes are conserved, I'm not sure what kind of unholy formula would predict the final pressure if only temperature is invariant as pressure and carbonation are mutually dependent. Such a formula may need to take into account the head volume, the volume of fluid etc. This thread talks about some similar stuff: https://www.homebrewtalk.com/threads/cold-crashing-under-pressure.690694, but I don't see anything that addresses precisely the question of how much and how fast will the pressure drop when keeping something cold for an extended period as with lagering.

My hypothesis would be that carbonation is a horizontal asymptote so it starts out quick and slows down.

But to the point, is a pressure gauge supposed to work if it is itself at lagering tempeatures? Maybe I should just rename this thread and make it a thread about spund lagering. My daily pressure reading should give us the rough outline of the asymptote.

 

[sibelman]

I would expect the gauge to work okay at low temperature. I've had some gauges work poorly at low pressure.

Yes, not only will the gas pressure drop because it's cooler, but it will also absorb better into the cooler liquid, lowering the pressure further. So time is also a factor. I've got no formulas though.

Carbonated sparkling fruit wine?

 

[PCABrewing]

But to the point, is a pressure gauge supposed to work if it is itself at lagering tempeatures?

The Oil Filled gauge should continue to work. If there was a spec limit I would expect them to provide that data, perhaps on the back.
The oil is in there to dampen movement and that effect may increase with colder ambient temp depending on the type of oil they used. But it should still respond to changes perhaps just a bit more slowly.

 

[beren]

Oil isn’t usually need unless there’s a lot of vibration like on a compressor, but until the temp is cold enough to thinken it so much the resistance is greater than the spring it should be ok. What oil is in it? Glycerin low range is +40F. https://www.ametekusg.com/learningzone/pressure-gauges/temperature-effects-on-pressure-gauges

 

[hotbeer]

You asking how temperature might affect the pressure gauge itself aren't you?

The specifications for your pressure gauge should tell you what environmental conditions it's designed to work in. You might can find them on the manufacturer's website if you tossed the papers that came with it. Or maybe email them the model you have and ask them.

 

[iandanielursino]

Carbonated sparkling fruit wine?

Yeah like I said I just got my stuff holding pressure and didn't have time for a brewday so it's a bizarre 80 F quick-wine which I am now lagering for no other reason than an equipment test.

Oil isn’t usually need unless there’s a lot of vibration like on a compressor, but until the temp is cold enough to thinken it so much the resistance is greater than the spring it should be ok. What oil is in it? Glycerin low range is 40. https://www.ametekusg.com/learningzone/pressure-gauges/temperature-effects-on-pressure-gauges

It's Glycerin. I'm guessing its fine at +33 F or they would mention it somewhere. Seems normal for a brewer to freeze their conical.

I've got no formulas though.

Yeah that's what didn't occur to me at first, I'd never seen any formulas, tables, or much discussion at all about 100% natural carbonation. I'm down to 4.5 PSI now, so I don't think its happening on this batch. Maybe if I was going from a diactyl rest to 33 instead of from 80 it would be better, but maybe a 15 PSI tank can't do natural carbonation. I will plan on adding a carb stone soon. It occurs to me that homebrewers who claim to "naturally carbonate" are full of crap, they aren't bottling and carbonation doesn't fully complete until they set and forget it in their kegerator.

Volume could also make a difference, I'm doing 7 gallons right now in a tank that's for up to a 10 gallon batch, I'm guessing less headspace would mean less loss in pressure due to the gas cooling, but I would also assume it would increase the pressure losses due to carbonation. I wonder if it would help to do the cold crash very slowly, I assume not because after the diactyl rest in a normal lager process you would not have anything left to ferment.

 

[Bobby_M]

Have you tried pulling the vent plug out on the case for a second?

 

[mac_1103]

maybe a 15 PSI tank can't do natural carbonation

I think this might be it. 15 PSI at 68F is only going to get you to 1.7 volumes (1.4 at 80F). So if your fermenter can only handle 15 PSI then I don't know see you can fully carbonate your beer by spunding. Maybe if it's a lager yeast and you're really patient it would work at something like 50F?

It occurs to me that homebrewers who claim to "naturally carbonate" are full of crap, they aren't bottling and carbonation doesn't fully complete until they set and forget it in their kegerator.

I think a lot of people are doing exactly that - partial natural carbonation followed by force carbonating the rest of the way. Not that there's anything wrong with it. But you can naturally carbonate in a keg since kegs can handle a lot more than 15 PSI.

 

[Clint Yeastwood]

I put new oil-filled gauges on my old Taprite. Either they work, or I am deluding myself and have no idea what my actual pressures are.

 

[sibelman]

Either they work, or I am deluding myself

The accuracy is somewhat dubious. I hope for reasonable accuracy and good consistency. I suppose it's possible to calibrate against a gauge I somehow trust...

 

[Indian_villager]

Do you have a CO2 tank with constant gas supply to the fermenter as it is chilling? If not then your headspace pressure will go down due to the decrease in temperature causing the gas to contract and absorb into the liquid.

As for your question on oil filled gauges. The colder they get the more resistant they are to moving, it should still read the proper pressure but it may take a smidge more time for the needle to move through more viscous fluid.

 

[iandanielursino]

If not then your headspace pressure will go down due to the decrease in temperature causing the gas to contract and absorb into the liquid.

It's actually two separate processes I think. The temperature makes the gas contract, which occurs immediately. The new temperature and pressure conditions then influence the solubility of the CO2 into the fluid, which begins the long process of equalizing the level of dissolved CO2. That's why I was confused. I saw that the first process had completed and assumed that the second would be negligible, but apparently the amount of actual gas which goes into your solution as "carbonation" is high enough to make a big impact on your pressure (at this size tank and amount of fluid anyway).

There being two processes at work also explains why you can get vaccum when lowering the temperature, but you can't (usually) get vaccum from the carbonation that occurs after, which I think was mentioned in another thread. The pressure loss due to temperature is a linear function but the pressure loss due to carbonation is an asymptote.

I think this might be it. 15 PSI at 68F is only going to get you to 1.7 volumes (1.4 at 80F). So if your fermenter can only handle 15 PSI then I don't know see you can fully carbonate your beer by spunding. Maybe if it's a lager yeast and you're really patient it would work at something like 50F?

I think a lot of people are doing exactly that - partial natural carbonation followed by force carbonating the rest of the way. Not that there's anything wrong with it. But you can naturally carbonate in a keg since kegs can handle a lot more than 15 PSI.

Yeah that's basically my conclusion. There's nothing wrong with partially carbonating during the fermentation and/or lagering and then finishing it off with CO2 from a bottle. This actually seems like the best process and what most pros would be doing. Pros usually do not spund much but they do have pressure worthy vessels for at least some part of the process and I would assume they use CO2 cannisters to prevent vacuum during lagering, either in the fermenter or in a separate tank, so they ARE partially carbonating to some extent. I will soon add a CO2 bottle, a carb stone, and a beer gun to my kit, and either hook up a regulator at the start of lagering, or else force carbonate after lagering.

You could spund carbonate in a keg the way Germans do by adding more sugar after the main fermentation (if you don't want to raise the pressure over 15 during the main fermentation to avoid messing with the yeast that is). But then you don't have your nice conical and racking arm allowing you to discard the bottom .5 gallons, and you add some sulfur smell like the Germans do. I suppose you could also spund up, cold crash, then pressure transfer from your conical into a keg which has a bit of sugar so that it krausens up to your desired pressure, then cold crash it a second time and lager it. I'm not sure how much of a difference it would make doing one cold crash in the conical and then an extended lagering in the keg. It wouldn't give any better results than using CO2 from a can though, that's for sure.

What I really want is home-brew CO2 reclamation so I could put my surplus CO2 in a bottle.

Also something I've been curious about for a while is how a brewer like Deschutes does bottle conditioning in a pro setting. I'm guessing the beer is partially carbonated from the fermentation and cold crash and they just counterpressure fill the bottles and add more sugar with a pipette. If for some reason I wanted to bottle condition even after getting CO2 equipment, I would probably do it exactly in this manner. Also if I was doing something that is supposed to have ester like a hefeweisen I would probably attach both the spunding valve and a blowoff with a valve, and shut off the blowoff once I get toward the end of fermentation just so I can cold crash off spund. Then force carbonate after. Though I have seen no scientific evidence that pressure actually prevents ester formation, and with spunding you don't start out under pressure it's only built after the critical phase for esters anyway.

BTW, the pressure was 4.5 yesterday and 4 today. It seems each day the amount of pressure in the last few days is approximated by the recursive function f(n) = f(n-1) - c (1/ (2^n)) where c is a coefficient for the initial pressure loss depending on which day you start on, ie the amount it decreases each day is half of how much it decreased the previous day. I wonder what the asymptote is. I imagine when the pressure stops changing that is equilibrium, and as long as the gauge does not read 0 at that point it proves I don't have any kind of a pressure leak.

 

[beren]

It's Glycerin. I'm guessing its fine at +33 F or they would mention it somewhere. Seems normal for a brewer to freeze their conical.

No, they may expect you to already know. A glycerin filled gauge is not normal for a brewer to use at all. The link I posted is applicable to all glycerin filled gauges, you have it out of spec.

 

[beren]

I put new oil-filled gauges on my old Taprite. Either they work, or I am deluding myself and have no idea what my actual pressures are.

From the link:
Accuracy
High and low temperatures affect accuracy on indication. A general rule of thumb for dry gauges is 1% of full scale change for every 50˚F change from 75˚F. This allowance should be doubled for gauges with liquid filled cases.

 

[whoaru99]

I suppose it's possible to calibrate against a gauge I somehow trust...

Indeed. At work we use three different devices.

One is a gauge comparitor which is used to check the gauge in question against a calibrated, high accuracy test gauge.

The second is a deadweight tester that's a primary reference standard with range from 5psi to 10000psi. Then, for lower pressure, a different unit for -5psi to 5psi.

A bit overkill for home brewing but access to such things and other nifty gadgets comes in handy at times.

 

[iandanielursino]

No, they may expect you to already know. A glycerin filled gauge is not normal for a brewer to use at all. The link I posted is applicable to all glycerin filled gauges, you have it out of spec.

Oh I read it wrong. It's not very far out of spec though at 33. Does it break it or just make it inaccurate while it's cold?

Looks like all the other gauges I would be interested in buying are also filled with glycerin:

https://brewbuilt.com/products/brewbuilt-stainless-15-tc-pressure-gauge-030-psi.html
https://www.gwkent.com/25in-dial-0-...hsa_ad=&hsa_tgt=&hsa_kw=&hsa_mt=&gad_source=1

From the link:
Accuracy
High and low temperatures affect accuracy on indication. A general rule of thumb for dry gauges is 1% of full scale change for every 50˚F change from 75˚F. This allowance should be doubled for gauges with liquid filled cases.

What does it mean by 1% full scale change? Still, sounds like it would only be < 2% off. This gauge doesn't even read as accurately as a single percent of its maximum peg. 2% I guess you can read, that would be just over half a PSI.

If the gauge does not work at lagering temperatures I guess that's all the more reason to forced carb afterwards lol.

Spike says never to valve off or remove the PRV/gauge/spunding-valve/gas-post combo without attaching a blowoff, but if I'm chilling it down why not? Its not like the pressure is going to go up. Do they not expect people to use conicals in a fermentation chamber but only with an immersion chiller? Potentially another reason not to use an all in one unit like spike's. Valving off and removing just a regular gauge would be less dangerous than doing it to your spunding valve which is also your only PRV. I could always calibrate my spunding valve to like 12 PSI and use a redundant PRV calibrated to 1 BAR for safety. Since I realized it is not realistic to spund carbonate from the primary fermentation at 15 PSI or under, I suppose I actually do not care what pressure the beer is at, I would say my goals in spunding are just 1. keep it under positive pressure for sanitation, 2. keep the pressure high enough that it doesn't become negative when chilling. Other stuff I can just use a CO2 tank for.

 

[whoaru99]

Using a 100psi gauge for example, 1% Full Scale would be 1psi.

That means the error due (in this exampe) to temperature would be 1 psi.

If the pressure being measured was 90 psi, 1 psi extra error wouldn't be that big of a deal.

But, if you're measuring 10psi with this example gauge, that 1psi is a bigger factor because it's 10% of what you're trying to measure.

But, fortunately, home brewing and carbonating is reasonably tolerant so that temperature error, IMO, isn't much to get excited over.

 

[iandanielursino]

Sure but this is a 30 PSI gauge and it only lets me read half PSIs anyway. A full 2% error could make it basically +/- 1 gradation. I'm only concerned if it would harm the gauge, since it isn't necessary for me to have a precise pressure reading during lagering.

Though, since the tank only can handle 15 PSI I suppose using it as a brite tank it needs to remain cold. But I could bring the temp up to 40 F and still hit most carbonation targets without exceeding 15 PSI.

 

[whoaru99]

Sure but this is a 30 PSI gauge and it only lets me read half PSIs anyway. A full 2% error could make it basically +/- 1 gradation. I'm only concerned if it would harm the gauge, since it isn't necessary for me to have a precise pressure reading during lagering.

I gave an easy example for your question what 1% FS is about presuming people can run with the example and scale it accordingly.

The question about gauge damage is a different question and I believe already answered.

 

[iandanielursino]

I wonder if it matters if you use a carb stone at the end or just a gas post the entire time if you're lagering for 3 weeks anyway. Seems like if the gauge reads better at 40 I should just wait until the end, raise the temp to 40 and forced carb it at that point. Would going up to 40 without racking undo the cold crash or lagering at all?

 

[whoaru99]

What's the acronym? RAHAB.

 

[cfrazier77]

Have you tried pulling the vent plug out on the case for a second?

This, there normally is a rubber plug for this.

 

[iandanielursino]

This, there normally is a rubber plug for this.

Oh thats what he meant. To equalize the pressure?

 

[doug293cz]

The temp probe is just in a well in the front of the tank so I think the wine had already gotten to 33 when it was 8.5 PSI. But yeah I suppose I would expect that for 2 or 3 weeks it will continue to gradually lose pressure as the carbon dioxide enters the fluid until it reaches equilibrium, I wasn't expecting it to be so drastic but maybe that is naïve. Starting to think with a 15 PSI system I may not be able to carb while lagering purely from spund, but that's fine I can just add some CO2 during the lagering process to keep it at the target pressure.

This is a pretty extreme test though I went all the way from 80 to 33, usually it would be like 68 for a diactyl rest down to 33.

Looking at a chart that actually goes up to 80, https://cdn.homebrewtalk.com/images/1/0/2/7/4/6/preschart1-68415.jpg there was only about 1.42 vol before the crash. I'm not sure what that means really, neither pressure nor volumes are conserved, I'm not sure what kind of unholy formula would predict the final pressure if only temperature is invariant as pressure and carbonation are mutually dependent. Such a formula may need to take into account the head volume, the volume of fluid etc. This thread talks about some similar stuff: https://www.homebrewtalk.com/threads/cold-crashing-under-pressure.690694, but I don't see anything that addresses precisely the question of how much and how fast will the pressure drop when keeping something cold for an extended period as with lagering.

My hypothesis would be that carbonation is a horizontal asymptote so it starts out quick and slows down.

But to the point, is a pressure gauge supposed to work if it is itself at lagering tempeatures? Maybe I should just rename this thread and make it a thread about spund lagering. My daily pressure reading should give us the rough outline of the asymptote.

Yeah like I said I just got my stuff holding pressure and didn't have time for a brewday so it's a bizarre 80 F quick-wine which I am now lagering for no other reason than an equipment test.


It's Glycerin. I'm guessing its fine at +33 F or they would mention it somewhere. Seems normal for a brewer to freeze their conical.


Yeah that's what didn't occur to me at first, I'd never seen any formulas, tables, or much discussion at all about 100% natural carbonation. I'm down to 4.5 PSI now, so I don't think its happening on this batch. Maybe if I was going from a diactyl rest to 33 instead of from 80 it would be better, but maybe a 15 PSI tank can't do natural carbonation. I will plan on adding a carb stone soon. It occurs to me that homebrewers who claim to "naturally carbonate" are full of crap, they aren't bottling and carbonation doesn't fully complete until they set and forget it in their kegerator.

Volume could also make a difference, I'm doing 7 gallons right now in a tank that's for up to a 10 gallon batch, I'm guessing less headspace would mean less loss in pressure due to the gas cooling, but I would also assume it would increase the pressure losses due to carbonation. I wonder if it would help to do the cold crash very slowly, I assume not because after the diactyl rest in a normal lager process you would not have anything left to ferment.

It's actually two separate processes I think. The temperature makes the gas contract, which occurs immediately. The new temperature and pressure conditions then influence the solubility of the CO2 into the fluid, which begins the long process of equalizing the level of dissolved CO2. That's why I was confused. I saw that the first process had completed and assumed that the second would be negligible, but apparently the amount of actual gas which goes into your solution as "carbonation" is high enough to make a big impact on your pressure (at this size tank and amount of fluid anyway).

There being two processes at work also explains why you can get vaccum when lowering the temperature, but you can't (usually) get vaccum from the carbonation that occurs after, which I think was mentioned in another thread. The pressure loss due to temperature is a linear function but the pressure loss due to carbonation is an asymptote.


Yeah that's basically my conclusion. There's nothing wrong with partially carbonating during the fermentation and/or lagering and then finishing it off with CO2 from a bottle. This actually seems like the best process and what most pros would be doing. Pros usually do not spund much but they do have pressure worthy vessels for at least some part of the process and I would assume they use CO2 cannisters to prevent vacuum during lagering, either in the fermenter or in a separate tank, so they ARE partially carbonating to some extent. I will soon add a CO2 bottle, a carb stone, and a beer gun to my kit, and either hook up a regulator at the start of lagering, or else force carbonate after lagering.

You could spund carbonate in a keg the way Germans do by adding more sugar after the main fermentation (if you don't want to raise the pressure over 15 during the main fermentation to avoid messing with the yeast that is). But then you don't have your nice conical and racking arm allowing you to discard the bottom .5 gallons, and you add some sulfur smell like the Germans do. I suppose you could also spund up, cold crash, then pressure transfer from your conical into a keg which has a bit of sugar so that it krausens up to your desired pressure, then cold crash it a second time and lager it. I'm not sure how much of a difference it would make doing one cold crash in the conical and then an extended lagering in the keg. It wouldn't give any better results than using CO2 from a can though, that's for sure.

What I really want is home-brew CO2 reclamation so I could put my surplus CO2 in a bottle.

Also something I've been curious about for a while is how a brewer like Deschutes does bottle conditioning in a pro setting. I'm guessing the beer is partially carbonated from the fermentation and cold crash and they just counterpressure fill the bottles and add more sugar with a pipette. If for some reason I wanted to bottle condition even after getting CO2 equipment, I would probably do it exactly in this manner. Also if I was doing something that is supposed to have ester like a hefeweisen I would probably attach both the spunding valve and a blowoff with a valve, and shut off the blowoff once I get toward the end of fermentation just so I can cold crash off spund. Then force carbonate after. Though I have seen no scientific evidence that pressure actually prevents ester formation, and with spunding you don't start out under pressure it's only built after the critical phase for esters anyway.

BTW, the pressure was 4.5 yesterday and 4 today. It seems each day the amount of pressure in the last few days is approximated by the recursive function f(n) = f(n-1) - c (1/ (2^n)) where c is a coefficient for the initial pressure loss depending on which day you start on, ie the amount it decreases each day is half of how much it decreased the previous day. I wonder what the asymptote is. I imagine when the pressure stops changing that is equilibrium, and as long as the gauge does not read 0 at that point it proves I don't have any kind of a pressure leak.

You've got a good understanding of the basic physics of what's going on during cold crashing. Attached is my pressurized cold crash calculation spreadsheet (in Excel and LibreOffice formats.)

You are correct that approach to equilibrium is an asymptotic process. This is because the closer you are to equilibrium, the slower the absorption of CO2.

Brew on

 

[cfrazier77]

Oh thats what he meant. To equalize the pressure?

Correct, you do this while it is not under pressure. If at no pressure your gauge does not read zero then doing this should bring it back down to zero. Non oil filled gauges are open to atmospheric pressure changes so they don't need this. Oil filled are sealed, so this needs to be done every so often. Just make sure that you do this with the plug in the up position.

 

[iandanielursino]

It seems to have stopped at 3.5 PSI. I thought equilibrium takes like 3 weeks? Does it take longer longer the more CO2 you force in with a regulator vs keeping the pressure unconstrainted?

 

[doug293cz]

It seems to have stopped at 3.5 PSI. I thought equilibrium takes like 3 weeks? Does it take longer longer the more CO2 you force in with a regulator vs keeping the pressure unconstrainted?

If you are just reabsorbing CO2 from the headspace in a closed system (your case), the amount of CO2 that gets absorbed is a fraction of that required to fully carbonate (with continuous CO2 resupply), so yes it takes less time to get close to equilibrium.

Did you try using the calculator I posted a few posts back. It should tell you the final equilibrium pressure if you feed it the correct inputs for your system.

Brew on

 

[iandanielursino]

It doesn't want to open in web office, I'll install libre office later on my other computer.

 

[beren]

I’m curious, does the gauge go to zero if you pull the pressure release? Since you’re out of spec for a glycerin pressure gauge it might not go to zero or it might be a few psi off because of the resistance of the cold glycerin

 

[whoaru99]

If you are just reabsorbing CO2 from the headspace in a closed system (your case), the amount of CO2 that gets absorbed is a fraction of that required to fully carbonate (with continuous CO2 resupply), so yes it takes less time to get close to equilibrium.

Did you try using the calculator I posted a few posts back. It should tell you the final equilibrium pressure if you feed it the correct inputs for your system.

Brew on

Bit of a different question, but could the "one shot" headspace pressure to carb a beer to equilibrium be calculated?

I don't mean like set it to 12psi (or whatever) and forget it for two weeks, I mean like put 5 gal of beer from fermenter into a corny keg then hit it with one charge of CO2 that would in time to bring it to 2.5vol from residual of 0.9 vol. What pressure would that take, in theory?

 

[beren]

Bit of a different question, but could the "one shot" headspace pressure to carb a beer to equilibrium be calculated?

I don't mean like set it to 12psi (or whatever) and forget it for two weeks, I mean like put 5 gal of beer from fermenter into a corny keg then hit it with one charge of CO2 that would in time to bring it to 2.5vol from residual of 0.9 vol. What pressure would that take, in theory?

Depends on the headspace. I image it would be quite high

 

[iandanielursino]

Depends on the headspace. I image it would be quite high

I think so, this is what I was missing when I started this. Looking at how full natural carbonation is done in Germany, it seems they add sugar to krausen up additional pressure far in excess of what you would want during fermentation before the cold crash, and this is supposedly why in some German beers you can detect a note of sulfur in the nose that goes away after a minute. From that concept I assume that its something you could do (whether with a cannister or using priming sugar) in a high pressure vessel, perhaps a keg, but you certainly cannot do it in a normal conical.

 

[beren]

Just some really rough math. Let’s say at a temp you need 10psi for 5 gal beer and 1/2 gal headspace and you wanted 2.5vol co2. The headspace is 1/10 the volume of the beer. The beer has 2.5 * 10 = 25 the volume of co2 as empty headspace. 25 * 10psi = 250 psi. This does not add in the small amount of additional co2 needed for the headspace itself, nor and co2 dissolved in the beer. If you let it sit for weeks there is less than .9 vol. It does slowly come out of solution.

 

[mac_1103]

I mean like put 5 gal of beer from fermenter into a corny keg then hit it with one charge of CO2 that would in time to bring it to 2.5vol from residual of 0.9 vol. What pressure would that take, in theory?

Depends on the headspace. I image it would be quite high

OK, redid my estimates... So assuming a five gallon corny I think you'd have to reduce the beer volume to about 4 gallons to have a realistic shot at making this work. With ~15 liters of beer and ~5 liters of headspace, 60 PSI should give you ~48 grams of CO2 in the headspace which should add ~1.63 volumes of carbonation when fully absorbed into the beer.

 

[beren]

At what temp?

 

[mac_1103]

68F. Still not quite right though, since I didn't account for the CO2 left in the headspace at equilibrium.

 

[mac_1103]

And anyway, I don't think anybody should actually try this based on my paper napkin arithmetic.

 

[beren]

I'm pretty sure your math is way off. at 30psi at 65°F on a tank you get 2.5vol equilibrium.