Unitank and spunding

[paque]

Hi!

It’s has been 3 days since I pitched my yeast and so far fermentation seems to go well…I’m gonna take a sample on day 4 of fermentation to look where my fermentation is at…I’m planning to connect for the first time a spunding valve to complete the fermentation process within a pressured Unitank…

1. Is there a rule of thumb about when it’s a good time to close the blowoff and connect the spunding valve and to finish the fermentation under pressure?
2. I usually cold crahs my beers…so I guess that the cold crashing process will make the Co2 in the headspace will tend to dissolve in the beer…to avoid a vaccum, at that time, I will plug my gas line to make sure that the pressure in the headspace remain the same…is that ok?
3. Do I have to match the headspace pressure befor cold crashing or I set the regulator at the PSI needed once the beer is cold? I mean, once the beer at 37F, according to the carbonation chart, I should set my Co2 regulator at 9 PSI….let’s that the headspace pressure is at 12 PSI before cold crashing…do I set my Co2 regulator at 9 PSI and the Co2 will then only being provided into the Unitank once the Co2 absorption makes the pressure goes down under 9 PSI? Could there be a kind of a blowback effect?
   1. What if my headpressure berfore cold crahsing is lower than the pressure I will need when the beer is gonna be cold?
4. Is it better to plug my gas line to the blowoff cane or at the carbonation stone to provide the Co2?

FYI, I brewed a Scotch ale…OG = 1.071 and FG = 1.023

Thanks a lot for you advices!

Simon

 

[paque]

You don't need to worry about negative pressure or suck-back, because you have an excess of positive pressure in the Unitank. As the temperature goes down, so does the pressure, but it is still positive pressure. Let's say you want your beer carbonated to 2.5 volumes (just about right for most lagers and ales). At 15 psig and 65F temperature you're only carbed to 1.7 volumes, but when you lower the temperature to 38F, your tank pressure will be 11 psig but the CO2 volumes will be 2.47, right at your desired 2.5 volumes carbonation. You'll be perfectly carbed up and cold crashed without any danger of sucking up Star San or imploding your Unitank, all in one easy step!

I think I’ve found my answer in another thread…my understanding is that even if the pressure goes down while cold crashing, it’s sitll a positive pressure…so I don’t have to worry about any negative pressure…I’m a right?

 

[Indian_villager]

1) Rule of thumb is .020 gravity points before your target FG. You can change this however you like
2) As you stated you'll still be at positive pressure with the spunding valve so no need to worry about oxidation.
3)The post you quoted seems to sum it up well
4) Are you asking where to hook up CO2 in order to carbonate your beer? If so the carbonation stone.

 

[Bassman2003]

I am a little confused with number 3 & 4. I will share how I approach it and maybe it can help sort out any questions.

Run your fermentation at the temperature you desire. Lets say 65F. Look at your carbonation chart to see the volume of CO2 you desire in your finished beer and see how much pressure is needed to achieve that at 65F. This is your target for the spunding valve pre cold crash. You can put the spunding valve on at any time (from the start would be a pressure ferment) but anything after 1.020 is fine. Since you will not be transferring your beer (unitank) then once you hit your spunding pressure you are done. Just perform your cold crash. The pressure in the unitank will go down as the temperature goes down. So you do not even need to disconnect the spunding valve as it will be set to a higher number, therefore it will be closed.

The key is to look at volumes of CO2 instead of pressure to consider your carbonation. This remains constant in a closed tank as the temperature fluctuates.

Spunding is actually easier than the other methods. Just set it and your are done. No need for any tank CO2.

 

[paque]

I am a little confused with number 3 & 4. I will share how I approach it and maybe it can help sort out any questions.

Run your fermentation at the temperature you desire. Lets say 65F. Look at your carbonation chart to see the volume of CO2 you desire in your finished beer and see how much pressure is needed to achieve that at 65F. This is your target for the spunding valve pre cold crash. You can put the spunding valve on at any time (from the start would be a pressure ferment) but anything after 1.020 is fine. Since you will not be transferring your beer (unitank) then once you hit your spunding pressure you are done. Just perform your cold crash. The pressure in the unitank will go down as the temperature goes down. So you do not even need to disconnect the spunding valve as it will be set to a higher number, therefore it will be closed.

The key is to look at volumes of CO2 instead of pressure to consider your carbonation. This remains constant in a closed tank as the temperature fluctuates.

Spunding is actually easier than the other methods. Just set it and your are done. No need for any tank CO2.

If I read the carbonation chart correctly, I should set the spunding valve at 25 psi at 65F in order to get a 2.3 vol of CO2 in my beer…The problem here is that my Unitank is rated to a max psi of 30, but has a pressure releive valve rated at 15 psi…. According to this, I need to add gas somewhere during or after the cold crash as my volume of CO2 provided by the fermention will not be high enough due to the PRV…

 

[Bassman2003]

That is a problem! 15 PSI is pretty restrictive. Is there a way to upgrade the PRV?

 

[paque]

That is a problem! 15 PSI is pretty restrictive. Is there a way to upgrade the PRV?

I wrote to SS Brewtech to find out if there is any other PRV with a higher range that could fit my Unitank…

 

[Bassman2003]

Any way to screw on a cornie PRV?

 

[Virus467]

Any way to screw on a cornie PRV?

I think cornie PRVs release at 60 - 100 psi. Definitely want something that would release at or below max design pressure since these are safety devices.

 

[GlueMan]

It might not be practical or possible to get your beer fully carbonated in the fermentor without an external CO2 source. At room temperature you'd need more pressure than the vessel should safely see (~30 psi). At cold temps (37 - 40 F) you'd still need ~11 psi to hit 2.5 volumes of CO2 and the yeast will stop fermenting before then.

I'm intrigued by the post that says 15 psi @ 65 F results in 11 psi @ 38 F....doesn't it depend on how much headspace you have? If there's only a small amount of air at 15 psi / 65 F I think it would drop to much less than 11 psi at 38 F, but I haven't tried it.

You might be able to hit ~2.4 volumes if you're using a lager yeast at ~48 F and ~ 15psi. Even though the conicals may be rated for 30 psi the manufacturers don't recommend it, and that's why the PRV's are usually set at 15 psi.

I usually close the blow-off and switch over to spunding when there are around 3 - 5 points left to go (I use a Tilt to monitor the gravity). More than that and the bubbles are too large for the sanitizer cup and it spills out. Though I guess you could cap it earlier and run without any water/sanitizer. No risk of suck-back when you have a constant pressure.

I usually spund to 6-8 psi at room temperature and 1-2 days after cold crashing it'll be sitting at ~3 psi. Crashing from lager temperatures will result in a smaller pressure difference. It's enough to get the keg transfer started but then I have to apply external CO2 pressure to get the rest of it done.

Let us know how it goes!

 

[Bassman2003]

I am pretty sure you can get different PSI ratings for the cornie style screw on PRVs. If the threads are the same on the vessel.

Glue, if you are adding tank CO2 to a spund then the reason for doing it is kind of lost. It is all about natural CO2 without and oxygen along with the convenience of reaching the target and being done.

 

[GlueMan]

Glue, if you are adding tank CO2 to a spund then the reason for doing it is kind of lost. It is all about natural CO2 without and oxygen along with the convenience of reaching the target and being done.

Understood, I was only trying to say that spunding to the necessary level can be difficult given the pressure limitations of a conical fermentor. You'd need 15-18 psi with a lager yeast but more like 28-30+ psi using an ale yeast (OP brewed a Scotch ale).

Now, spunding in a keg is another story...

 

[paque]

Here is the manufacturor response about using a PRV rated at a higer PSI than the one that comes with the Unitank:

« Thanks for your patience here! While our tanks are rated by us for 15 PSI Recommended Operating Pressure and 30PSI Manufacturer's Indicated Max Pressure through lots of durability and destruction tests, we do not use pressure-rating third-party certifications for every one of our vessels as this would likely double the cost overall per tank.

Because not all our tanks are not verified by a third party, such as ASME, we cannot advertise an operating pressure in excess of 15 PSI. Of course, all of our vessels are tested at pressures well in excess of 15 PSI and 30 PSI (well up to 60PSI). This is a legal consideration, not an operational one. If you wanted to use our pressure-capable tanks with a higher pressure PRV instead of our stock ones, you certainly could do that. »

If I’m reading correctly, I could use another PRV….

 

[paque]

It might not be practical or possible to get your beer fully carbonated in the fermentor without an external CO2 source. At room temperature you'd need more pressure than the vessel should safely see (~30 psi). At cold temps (37 - 40 F) you'd still need ~11 psi to hit 2.5 volumes of CO2 and the yeast will stop fermenting before then.

I'm intrigued by the post that says 15 psi @ 65 F results in 11 psi @ 38 F....doesn't it depend on how much headspace you have? If there's only a small amount of air at 15 psi / 65 F I think it would drop to much less than 11 psi at 38 F, but I haven't tried it.

You might be able to hit ~2.4 volumes if you're using a lager yeast at ~48 F and ~ 15psi. Even though the conicals may be rated for 30 psi the manufacturers don't recommend it, and that's why the PRV's are usually set at 15 psi.

I usually close the blow-off and switch over to spunding when there are around 3 - 5 points left to go (I use a Tilt to monitor the gravity). More than that and the bubbles are too large for the sanitizer cup and it spills out. Though I guess you could cap it earlier and run without any water/sanitizer. No risk of suck-back when you have a constant pressure.

I usually spund to 6-8 psi at room temperature and 1-2 days after cold crashing it'll be sitting at ~3 psi. Crashing from lager temperatures will result in a smaller pressure difference. It's enough to get the keg transfer started but then I have to apply external CO2 pressure to get the rest of it done.

Let us know how it goes!

I’m not sure to understand the physic laws regarding gas…I thought that the chart were design at equilibrium…meaning that regardless of my headspace, if the PSI stabilize at 15 at 65F, that would mean that the volume of dissolved CO2 in the beer would be the same…

Am I wrong?

 

[DuncB]

Good information about the pressure rating and the alternative PRV.

I regularly spund my fermentasaurus to 25 psi at the end of fermentation. Then when it's cold crashed more CO2 gets dissolved in solution and the headspace pressure drops pro rata. So if I've got to 2 vols at 20 celsius when crashed to 4 celsius the pressure falls but corresponds to 2 vols still. Does that help?

 

[Bassman2003]

Glad the manufacturer cut through the legal stuff to let you know you would be ok. Yes, there are three variables, pressure, temperature and volume. When the volume is fixed (vessel size) then the other two will adjust to find equilibrium. Nothing is gained or lost, just distributed differently. Going by the volumes of CO2 in the liquid on the charts helps define one piece of the puzzle so you can pick the other two.

Hope you can find a PRV that fits.

 

[paque]

Glad the manufacturer cut through the legal stuff to let you know you would be ok. Yes, there are three variables, pressure, temperature and volume. When the volume is fixed (vessel size) then the other two will adjust to find equilibrium. Nothing is gained or lost, just distributed differently. Going by the volumes of CO2 in the liquid on the charts helps define one piece of the puzzle so you can pick the other two.

Hope you can find a PRV that fits.

The thing that I still don’t undestand is about the volume…GlueMan abovre rose a good point…let’s say that we have on 7G fermentor with 5G of beer in it and and another fermenter with 5G of beer in it but that has a 14G capacity…

Obviously, I would have more headspace in the 14G fermentor than in the 7G…so if we both set fermenter at 15 PSI with a spunding valve, there will more CO2 in the headspace of the 14G fermenter I guess…

Frome there, I’m really confused…

 

[Bassman2003]

Well the way I see it, you will have different amounts of CO2 in each fermenter, but if the temps and pressures are set the same, you will end up with the same volume of CO2 absorbed in the wort/beer. So in the end, it does not matter about the headspace because the larger fermenter will retain more of the CO2 to find the right balance. The balance stays consistent across vessels, so all you have to focus on is the three variables. Does that help/make sense?

 

[DuncB]

I think @doug293cz did a spreadsheet to work this out. re headspace and pressure.

 

[doug293cz]

I think @doug293cz did a spreadsheet to work this out. re headspace and pressure.

Most of the posters here have the general concepts down, but all are missing some of the subtleties. I will post a detailed response later today.

Brew on

 

[doug293cz]

Ok, going to go thru the math of volumes first, and then use the math to demonstrate what happens in some actual cases.

First, what is a "volume"? A volume is actually a ratio of how much volume a given mass of CO2 would occupy at 0°C and 1 atmosphere of absolute pressure (14.695 psia) vs. what that same mass of CO2 currently occupies. For example if a beer has 2.5 volumes of carbonation, then the CO2 in 1 liter (or 1 gallon) of beer, would occupy 2.5 liters (or 2.5 gallons) of volume if it was a gas at 0°C and 1 atm of absolute pressure. 1 volume is equivalent to 1.977 g/L of CO2.

We also need to understand that for all physical processes, the pressure that matters is the partial pressure of each particular gas that is present. The partial pressure of a gas is the absolute pressure that a gas would have if it is the only gas present in an enclosed volume. The absolute pressure is gauge pressure plus 14.695 psi (since gauges measure the difference between atmospheric pressure and the vessel pressure) assuming that the gas in question is the only gas present. Conveniently, in a spunded fermenter, the only gas present is CO2 so the CO2 partial pressure is equal to the total absolute pressure (gauge pressure + 14.695 psi.)

Additionally, we need to understand that temperatures that affect physical process are absolute temperatures. The absolute temperature in °K is equal to °C + 273.15°.

So, prior to doing any calculations, we will convert all pressures from gauge pressure to absolute pressure using PA = PG + 14.685 psi, and convert all temps from °C to °K. We will then convert back to gauge pressure and °C after the calculations if needed.

We will do all calculations using mass (g) of CO2, and density of CO2 (g/L) and convert to volumes at the end of the calculations, using 1 volume = 1.977 g/L.

Now a couple of fundamental equations:

Concentration of CO2 in beer (g/L) = 1.977 g/L * (PA * (0.01821 + 8089.66 * exp(-TK / 23.95)) - 0.003342)​

after some algebra on equation 2.1 in the attached .pdf​

​

Concentration of CO2 in headspace (g/L) = 1.977 g/L * PA * 273.15°K / (14.695 * TK)​

after some algebra on the ideal gas law​

​

We can use the above two equations to calculate the concentration of CO2 in the beer and headspace, respectively, at the end of fermentation (the assumption is that CO2 in the beer and headspace are in equilibrium at the end of fermentation.)

We can then calculate the mass of CO2 in the beer and the mass of CO2 in the headspace by multiplying the concentrations by the volume of beer and the volume of headspace (both in liters.) The total mass of CO2 in the fermenter at the end of fermentation is the sum of the masses:

Total CO2 mass = 1.977 g/L * (Beer Vol [L] * (PA * (0.01821 + 8089.66 * exp(-TK / 23.95)) - 0.003342) ​

+ Headspace Vol [L] * PA * 273.15°K / (14.695 * TK))​

​

where PA = Absolute headspace pressure at the end of fermentation in PSI and TK = temperature in °K at the end of fermentation​

​

When we cold crash, the total mass of CO2 in the fermenter stays constant, so to determine the new headspace pressure after things come to equilibrium after cold crashing, we change the value of TK in the above equation to the cold crash temperature, and solve the equation for the new PA

To determine the headspace pressure immediately after cold crashing, before any additional CO2 gets absorbed by the beer, we use the following equation:

PA [cold] = PA [warm] * TK [cold] / TK [warm]​

​

That's all for tonight. I will solve the ugly equation for P tomorrow, work a couple of examples, and provide a spreadsheet to do the math.

Brew on

 

[doug293cz]

Ok, I think I have solved the "Total CO2 Mass" equation in the previous post for PA, and it looks like this:

PA = (VolB [L] * 0.003342 + CO2 [g] / 1.977 g/L) / ((VolB [L] *(0.01821 + 8089.66 * exp(-TK / 23.95)) ​

+ VolH [L] * 273.15°K / (14.695 * TK))​

​

Where VolB = Beer Volume and VolH = Headspace Volume​

​

You can check my algebra if you wish, but I have verified that the equation works in the attached spreadsheet (two versions in .zip file.)

Here's a screenshot of the spreadsheet. Input cells are outlined in blue and have blue text. You should not modify any cells other than the input boxes (if the sheet protection works correctly you won't be able to.) Note that the sheet includes °F to °C and gallons to liters unit converters since inputs need to be in °C and liters.

Notes:

1. The "Total CO2 Mass in Fermenter" is calculated twice as a check that all of the math is self consistent
2. The "Pressure after Equilibrium (PSI gauge)" cell will turn red if this number goes negative. A negative value indicates that you will create a partial vacuum in the fermenter if you cold crash long enough.

Notice that the pressure drop immediately after the temp change is small compared to the pressure drop after CO2 absorption from the headspace has reached equilibrium (2 psi vs. 12 psi.)

Play with the spreadsheet to see what happens with different scenarios. If you have comments or questions - let'm rip.

Brew on

 

[doug293cz]

I’m not sure to understand the physic laws regarding gas…I thought that the chart were design at equilibrium…meaning that regardless of my headspace, if the PSI stabilize at 15 at 65F, that would mean that the volume of dissolved CO2 in the beer would be the same…

Am I wrong?

The thing that I still don’t undestand is about the volume…GlueMan abovre rose a good point…let’s say that we have on 7G fermentor with 5G of beer in it and and another fermenter with 5G of beer in it but that has a 14G capacity…

Obviously, I would have more headspace in the 14G fermentor than in the 7G…so if we both set fermenter at 15 PSI with a spunding valve, there will more CO2 in the headspace of the 14G fermenter I guess…

Frome there, I’m really confused…

If you are providing external CO2 to the vessel, then pressure and temperature are the only things that affect the equilibrium carbonation level - headspace volume will have no effect.

However, if you spund without external CO2, then the headspace will affect the final equilibrium carbonation level after chilling. I have run two scenarios, all with 5.28 gal (20 L) of beer, 68°F (20°C) fermentation temp, 37°F (2.78°C) cold crash temp, and 15 psi (gauge) spunding pressure. The difference is in the fermenter volume. Case 1 is a 7 gal (26.5 L) fermenter volume and Case 1 is a 14 gal (53 L.) I have placed the results side by side below:

Notice that the headspace pressure immediately after cooling is the same in both cases, since the pressure change is due only to the temp change. The beer carbonation levels at that point are also the same, as no CO2 absorption from the headspace has taken place (this is only strictly true if you can cool instantaneously, but isn't too far off in the real world.) But, as CO2 starts getting absorbed into the cooler beer, things get very different.

Brew on

 

[doug293cz]

Well the way I see it, you will have different amounts of CO2 in each fermenter, but if the temps and pressures are set the same, you will end up with the same volume of CO2 absorbed in the wort/beer. So in the end, it does not matter about the headspace because the larger fermenter will retain more of the CO2 to find the right balance. The balance stays consistent across vessels, so all you have to focus on is the three variables. Does that help/make sense?

Not correct. Things are the same immediately after a very quick cold crash, but the amount of CO2 absorbed from the headspace will be more, if the headspace is larger, if everything else is equal. See my post immediately above this one.

Brew on

 

[paque]

If you are providing external CO2 to the vessel, then pressure and temperature are the only things that affect the equilibrium carbonation level - headspace volume will have no effect.

However, if you spund without external CO2, then the headspace will affect the final equilibrium carbonation level after chilling. I have run two scenarios, all with 5.28 gal (20 L) of beer, 68°F (20°C) fermentation temp, 37°F (2.78°C) cold crash temp, and 15 psi (gauge) spunding pressure. The difference is in the fermenter volume. Case 1 is a 7 gal (26.5 L) fermenter volume and Case 1 is a 14 gal (53 L.) I have placed the results side by side below:

View attachment 830416

Notice that the headspace pressure immediately after cooling is the same in both cases, since the pressure change is due only to the temp change. The beer carbonation levels at that point are also the same, as no CO2 absorption from the headspace has taken place (this is only strictly true if you can cool instantaneously, but isn't too far off in the real world.) But, as CO2 starts getting absorbed into the cooler beer, things get very different.

Brew on

First…THANKS a lot for all the data and info provided…and for the spreadsheets as welll…just wow!

Now…if my understanding is good…if someone just wants to rely only on the spunding valve to carb his beer…with a vessel limited to 15 psi, it would be a better choice to use a larger fermenter to capture more C02 within a larger headspace and then get more C02 in his beer at equilibrium….correct?

 

[paque]

I’m playing with the spreadsheet…so..for the next batch…if I buy a 22 psi PRV and set my spunding to 21 psi…then I could brew a smaller batch (17 L in a 26.5 L fermenter)…keep the beer at 21.5C at the and of fermentation and then cold crash the beer to 3.5C and then get 2.3 vol of C02 at equilibrium at that temp…

Now…the question will be: when do I have to close the blow off to still have enough CO2 to be produced by the fermentation in order to reach the 21 psi needed as per the spreadsheet…I guess that it’s only experience that will provide the answer to that question…

 

[doug293cz]

I’m playing with the spreadsheet…so..for the next batch…if I buy a 22 psi PRV and set my spunding to 21 psi…then I could brew a smaller batch (17 L in a 26.5 L fermenter)…keep the beer at 21.5C at the and of fermentation and then cold crash the beer to 3.5C and then get 2.3 vol of C02 at equilibrium at that temp…

Now…the question will be: when do I have to close the blow off to still have enough CO2 to be produced by the fermentation in order to reach the 21 psi needed as per the spreadsheet…I guess that it’s only experience that will provide the answer to that question…

It's possible to calculate how much fermentation is needed to generate the required amount of CO2 to reach a given pressure, but you have to have a pretty good idea what your FG will actually be. If your FG finishes higher than expected then your final pressure would be lower than desired. Of course the easiest would be to just pressure ferment from the start, and then you don't need to do any calculations to determine an SG at which to start spunding.

I'll start working on how to do the needed calculation.

Brew on

 

[DuncB]

That's great work

So currently my beer is spunded and stable at 22 celsius with gauge pressure of 13 psi
Beer volume is 18 litres
Headspace is 18 litres
I'm turning off the heat and letting it fall to ambient so we'll be able to see how the numbers go.
ambient will be about 12 Celsius but will confirm temp with next update.

 

[doug293cz]

That's great work

So currently my beer is spunded and stable at 22 celsius with gauge pressure of 13 psi
Beer volume is 18 litres
Headspace is 18 litres
I'm turning off the heat and letting it fall to ambient so we'll be able to see how the numbers go.
ambient will be about 12 Celsius but will confirm temp with next update.

With a slow cool, you will get some CO2 absorption during the cooling, so that when the beer reaches it's final temp, the headspace pressure will be lower than the "instantaneously" cooled pressure (I'd be interested to know by how much, and how long the cooling took.) It will also take a week or two to reach the equilibrium pressure at the cooler temp (just like set and forget forced carbing.)

Brew on

 

[DuncB]

With a slow cool, you will get some CO2 absorption during the cooling, so that when the beer reaches it's final temp, the headspace pressure will be lower than the "instantaneously" cooled pressure (I'd be interested to know by how much, and how long the cooling took.) It will also take a week or two to reach the equilibrium pressure at the cooler temp (just like set and forget forced carbing.)

Brew on

Yes I'm going to monitor and update, gravity has been stable on the ispindel for 6 days and the pressure so I'm hoping no more ferment occurs to skew the data collected.
I've not had the spunding valve on for several days so pressure stable with no spunding loss.
I do not measure atmospheric pressure when I take my readings as I don't think it's significant.

 

[Bassman2003]

Thank you Doug. Gases are quite interesting and I clearly have a lot to learn.

It seems the "carbonation charts" are missing a data point. Without knowing headspace volume, there is not way to accurately asses end CO2 volume in the beer. I think we need a new carbonation chart which has an input column for headspace volume.

From my over simplified view, it appears the amount of CO2 in a vessel determines the amount of absorbed CO2 in the beer and any given temp/pressure. Meaning larger vessels just hold more CO2 which in turn gets placed in the beer even though pressure and temperature remain constant.

Makes logical sense as if one had a fermenter with almost no headspace, theoretically spunding would let most of the CO2 leave the container as there is nowhere for it to go beyond the given pressure. So "headspace" is kind of like a "holding space" for CO2 that might get absorbed if pressure or temps change.

 

[doug293cz]

Thank you Doug. Gases are quite interesting and I clearly have a lot to learn.

It seems the "carbonation charts" are missing a data point. Without knowing headspace volume, there is not way to accurately asses end CO2 volume in the beer. I think we need a new carbonation chart which has an input column for headspace volume.

From my over simplified view, it appears the amount of CO2 in a vessel determines the amount of absorbed CO2 in the beer and any given temp/pressure. Meaning larger vessels just hold more CO2 which in turn gets placed in the beer even though pressure and temperature remain constant.

Makes logical sense as if one had a fermenter with almost no headspace, theoretically spunding would let most of the CO2 leave the container as there is nowhere for it to go beyond the given pressure. So "headspace" is kind of like a "holding space" for CO2 that might get absorbed if pressure or temps change.

The headspace only makes a difference if you are not hooked up to a regulated source of CO2. If you cold crash a spunded fermenter, with no provision for adding more CO2, then the pressure is not constant. Cold beer can hold more CO2 than warm beer at the same CO2 partial pressure, so if you cool down a sealed vessel, the beer will absorb some of the CO2 from the headspace, thus lowering the pressure in the headspace. There is also a pressure drop just due to cooling the gases in the headspace. The spreadsheet I posted above does the calculation (a mass balance) to determine how much CO2 gets absorbed, and what the resulting headspace partial pressure of CO2 will be, for a specific set of conditions.

The existing carbonation charts are fine for what they are intended for, which is the case of constant CO2 partial pressure, controlled by a regulator. A chart for a sealed cold crash situation would need to be four dimensional, as the variables are starting pressure, starting temperature, ending temperature, and headspace volume to beer volume ratio. The spreadsheet takes all four variables into account.

Brew on

 

[DuncB]

With a slow cool, you will get some CO2 absorption during the cooling, so that when the beer reaches it's final temp, the headspace pressure will be lower than the "instantaneously" cooled pressure (I'd be interested to know by how much, and how long the cooling took.) It will also take a week or two to reach the equilibrium pressure at the cooler temp (just like set and forget forced carbing.)

Brew on

So 36 litre fermenter, with 18.5 litres of belgian tripel, headspace 17.5 litres, was 13psi at stable ferment and 22C.

So a week falling to ambient 12C and then been cold crashed at 2.5 C for 20 days.

Gauge pressure now reads 10 psi.

This doesn't agree with the cold crash calculator spreadsheet. No change of gravity so not a case of more CO2 being made.

So do I have youc calculator values of 1.92 vols or do I have vols of the carbonation calculator tables ( electronic version) which would suggest for 10psi gauge at 2.5 celsius of 2.45 vols?

I'm wanting to pressure transfer and then add sugar to get to around 3.3 vols using your other clever calculator.
I'm wondering if I aim for adding sugar to boost vols of CO2 to 3.3 from 2.45 ( ie an increase of 0.85 vols).
Depending on the actual CO2 vols based on your calculator giving the figure of 1.92 then at least I'll be at 2.7 vols which is well within the ballpark.

My suspicion is that my CO2 vols are actually going to be nearer the 2.45 vols when I start this process.

Any ideas?

 

[doug293cz]

So 36 litre fermenter, with 18.5 litres of belgian tripel, headspace 17.5 litres, was 13psi at stable ferment and 22C.

So a week falling to ambient 12C and then been cold crashed at 2.5 C for 20 days.

Gauge pressure now reads 10 psi.

This doesn't agree with the cold crash calculator spreadsheet. No change of gravity so not a case of more CO2 being made.

So do I have youc calculator values of 1.92 vols or do I have vols of the carbonation calculator tables ( electronic version) which would suggest for 10psi gauge at 2.5 celsius of 2.45 vols?

I'm wanting to pressure transfer and then add sugar to get to around 3.3 vols using your other clever calculator.
I'm wondering if I aim for adding sugar to boost vols of CO2 to 3.3 from 2.45 ( ie an increase of 0.85 vols).
Depending on the actual CO2 vols based on your calculator giving the figure of 1.92 then at least I'll be at 2.7 vols which is well within the ballpark.

My suspicion is that my CO2 vols are actually going to be nearer the 2.45 vols when I start this process.

Any ideas?

I'm on vacation, so might not get to this right away (a week or so probably.)

Brew on

 

[DuncB]

I'm on vacation, so might not get to this right away (a week or so probably.)

Brew on

Have a great time.
I'm in no hurry whatsoever. It'll take 4 weeks or so to condition anyway before I test a bottle.