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

[mac_1103]

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

Is that assuming the standard 0.84 volumes at the end of fermentation? Because that would mean you got the same answer. 1.63 - 0.84 = 2.47. Alternatively it is in fact quite possible that I messed up.

edit - sorry, read your post wrong; but that's maintaining 30 PSI rather than a single charge of 30 PSI, right?

 

[doug293cz]

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

You can use the information in this post to do an accurate calculation.

Use the first part (the blue part) of the first equation to calculate the mass of CO2 in the beer at the end of fermentation. PA is the absolute fermentation pressure (14.7 psi for an open or airlocked fermentation, and 14.7 + gauge pressure for a pressure fermentation.) Then use the full first equation to calculate the mass of CO2 required in the keg. Here PA is 14.7 + gauge pressure for the desired level of carbonation. Now subtract the starting mass of CO2 in the beer from the total final mass of CO2 in the keg to give you how much CO2 you would have to force into the headspace. Now solve the second part of the first equation (the green part) for PA given the required headspace mass of CO2. Remember to subtract 14.7 from PA to get the gauge pressure.

For reference the total enclosed volume of a corny keg is 5.3 - 5.35 gal (20 - 20.25 L.)

Brew on

 

[whoaru99]

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

In this hypothetical question the beer is at 34F

 

[mac_1103]

In this hypothetical question the beer is at 34F

oops

 

[doug293cz]

You can use the information in this post to do an accurate calculation.

Use the first part (the blue part) of the first equation to calculate the mass of CO2 in the beer at the end of fermentation. PA is the absolute fermentation pressure (14.7 psi for an open or airlocked fermentation, and 14.7 + gauge pressure for a pressure fermentation.) Then use the full first equation to calculate the mass of CO2 required in the keg. Here PA is 14.7 + gauge pressure for the desired level of carbonation. Now subtract the starting mass of CO2 in the beer from the total final mass of CO2 in the keg to give you how much CO2 you would have to force into the headspace. Now solve the second part of the first equation (the green part) for PA given the required headspace mass of CO2. Remember to subtract 14.7 from PA to get the gauge pressure.

For reference the total enclosed volume of a corny keg is 5.3 - 5.35 gal (20 - 20.25 L.)

Brew on

I put together a little spreadsheet to do this calculation. For18.9 L (5 gal) of beer fermented at atmospheric pressure and 18°C (64.4°F) to be carbonated to 2.5 volumes at 4°C (39.2°F.) The headspace volume is 1.2 L. The required single shot CO2 pressure for this case is 390 psig! Here's a screen shot of the spreadsheet, and the sheet is attached below (LibreOffice format only.)

Brew on

 

[beren]

This seems about right. I know I over estimated the headspace volume to simplify things and was just trying to get an easy mash ideal gas law set up going. Cut the volume in half and the pressure doubles.

 

[mac_1103]

I put together a little spreadsheet to do this calculation.

So if it really meant that much to someone, it looks like you could probably do a single shot pressurization / carbonation at a reasonable gauge pressure of ~60 PSI in a refrigerated corny keg if you reduced the beer volume to about 3.5 gallons.

 

[iandanielursino]

The required single shot CO2 pressure for this case is 390 psig!

I wonder how them Germans go about spunding stuff fully carbonated then. Is it because they are still krausening it as they slowly lower the temperatures so that there is a constant pressure source?

So if it really meant that much to someone, it looks like you could probably do a single shot pressurization / carbonation at a reasonable gauge pressure of ~60 PSI in a refrigerated corny keg if you reduced the beer volume to about 3.5 gallons.

Or yeah use a lot more headspace than fluid.

 

[iandanielursino]

BTW the sanitizer cup is right over the rubber stopper on the gauge body so I can't really get at it right now. I stuck my fingernail in the edge and the gauge reading went up by 1 PSI from 3.5 to 4.5.

I imagine the air bubble at the top of the gauge was under less pressure than it usually would due to being made cold, so the pressure has now I imagine assumed atmospheric pressure, so I'm guessing the reading it has now is more accurate.

I don't want to mess with it any more but I can try and do other experiments when my trial lagering is over.

 

[whoaru99]

I put together a little spreadsheet to do this calculation. For18.9 L (5 gal) of beer fermented at atmospheric pressure and 18°C (64.4°F) to be carbonated to 2.5 volumes at 4°C (39.2°F.) The headspace volume is 1.2 L. The required single shot CO2 pressure for this case is 390 psig! Here's a screen shot of the spreadsheet, and the sheet is attached below (LibreOffice format only.)


Brew on

Holy pressure vessel Batman!

Kids don't try that at home.

Thank you for doing that.

 

[doug293cz]

I wonder how them Germans go about spunding stuff fully carbonated then. Is it because they are still krausening it as they slowly lower the temperatures so that there is a constant pressure source?

When spunding, you have active fermentation going on, which creates CO2 in the beer. Then "excess" CO2 diffuses out of the beer to pressurize the headspace, and keep the headspace pressure in equilibrium with the carbonation level in the beer. As spunding continues, the carbonation level increases, as does the headspace pressure, but the headspace pressure is never above the equilibrium pressure (which is a requirement for forced carbonation.)

In the single shot forced carbonation case, there is no CO2 being produced within the beer, and all of the CO2 needed to carbonate the beer (less the residual CO2 from primary fermentation) must come from the headspace. If the headspace is small compared to the beer volume, then high pressures are required to get the requisite amount of CO2 in the headspace to start.

Brew on

 

[iandanielursino]

When spunding, you have active fermentation going on, which creates CO2 in the beer. Then "excess" CO2 diffuses out of the beer to pressurize the headspace, and keep the headspace pressure in equilibrium with the carbonation level in the beer. As spunding continues, the carbonation level increases, as does the headspace pressure, but the headspace pressure is never above the equilibrium pressure (which is a requirement for forced carbonation.)

In the single shot forced carbonation case, there is no CO2 being produced within the beer, and all of the CO2 needed to carbonate the beer (less the residual CO2 from primary fermentation) must come from the headspace. If the headspace is small compared to the beer volume, then high pressures are required to get the requisite amount of CO2 in the headspace to start.

Brew on

So they need to reach an equilibrium (or guess what it will be) before they cold crash from their krausening which will allow them to have the right amount of CO2 in headspace and dissolved to reach the right equilibrium at cold crash/lagering and bottling.

I imagine that takes < 45 PSI

 

[doug293cz]

So they need to reach an equilibrium (or guess what it will be) before they cold crash from their krausening which will allow them to have the right amount of CO2 in headspace and dissolved to reach the right equilibrium at cold crash/lagering and bottling.

I imagine that takes < 45 PSI

No guessing needs to be involved. If you spund to the correct pressure, you will have the desired amount of carbonation in the beer. The spunding valve will release any excess CO2 from the headspace and beer. Cold crashing by itself doesn't change the amount of CO2 in the beer, but if you hold the cold crash for several days, you will absorb a little CO2 from the headspace. The larger the headspace to beer volume ratio, the more CO2 will be absorbed from the headspace when equilibrium is reached.

The spreadsheet I attached to this post will calculate the pressure drop in the headspace when cold crashing a sealed vessel, the amount of CO2 absorbed from the headspace by the beer, and the final carbonation level if you cold crash long enough to reach equilibrium. Below is an example calculation:

Assume you are fermenting 40 L (~10.6 gal) of beer in a 53 L (14 gal) fermenter at 10°C (50°F) and want 2.5 volumes of carbonation at the end of fermentation. Based on carbonation charts or calculators, you would set your spunding valve to 17.6 psi. If you then cold crash to 2°C (35.6°F), and wait long enough for the headspace to come into equilibrium with the beer, the headspace pressure will reduce to 11.3 psi, and the beer carbonation level will increase to 2.62 volumes. An increase in carbonation of only 0.12 volumes.

Brew on

 

[iandanielursino]

but if you hold the cold crash for several days, you will absorb a little CO2 from the headspace.

I did say cold crash/lagering. Lagering is going to be at equilibrium by the end so it will definitely change the amount of CO2. The general case is you do have to consider it, its only in the specific case of a short cold crash you don't.

 

[doug293cz]

I did say cold crash/lagering. Lagering is going to be at equilibrium by the end so it will definitely change the amount of CO2. The general case is you do have to consider it, its only in the specific case of a short cold crash you don't.

As far as lagering goes, it will depend on if you bulk lager in the fermenter and let the headspace pressure and CO2 pick-up do what they will. Or, if you transfer the beer to a bright tank or package the beer for lagering, where you can adjust the headspace CO2 partial pressure to a value that will leave you with what you want after lagering.

As the example shows, it only makes a small difference (~0.1 volumes.) If that is important to you, then you can compensate for it in several ways.

• Minimize the cold crash time to minimize the CO2 pick-up. This is something commercial brewers are particularly interested in doing, since time is real money to them.
• If you are going to cold crash to equilibrium CO2 pick-up, you can spund to a slightly lower pressure such that the CO2 pick-up during cold crashing will put you at your target volumes when equilibrium is reached.
• Reduce the headspace CO2 partial pressure as the temperature drops during cooling, such that the headspace pressure remains in equilibrium at the instantaneous temperature and the current (desired) beer carbonation level.

Brew on