Positive pressure cold crash

[jddevinn]

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.

How did you calculate this? Unless I' missing something the initial specific volume of the CO2 is dependent on both pressure and the temperature and therefore not completely defined here. Without knowing the specific volume the mass of CO2 cannot be calculated.If you assume a pressure at the beginning of your calc you will still need to account for the (massive) amount of CO2 absorption into the beer. Fact is if you pressurise to 10psi and come back with NO TEMPERATURE CHANGE head pressure will be almost nill in a day or so (probably a couple days on a 1/2 gas 1/2 beer keg). Decreasing the temperature speeds up the CO2 absorption process and reduces the volume of the gas present.

Without a positive pressure cold crashing a sealed keg with that large of a CO2 volume does not sound like a good idea to me. Keg may not bust but you WILL have a negative pressure in the keg.

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.

No. Why would this particular CO2 stratify but the remainder of the CO2 in the atmosphere stay mixed and not you know create a "blanket" on the surface and kill you?

 

[Anyhowe]

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

Yea facts tend to do that sometimes.

So I think I will add 10psi and let folks know if there is positive, negative or no pressure in my corney after a 2 day 36 degree crash.

 

[jddevinn]

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?

I believe the calculation is underestimating the volume change in CO2 and incorrectly calculating the pressure change.

 

[Sailingeric]

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

This is what I do. The first pint I pull will have some trub but after that it is good to go, and if there is a little haze it will fall in a week or so as well.

 

[jddevinn]

Yea facts tend to do that sometimes.

So I think I will add 10psi and let folks know if there is positive, negative or no pressure in my corney after a 2 day 36 degree crash.

If the purpose of this is simply not to carbonate before racking...... you do realize that the beer already will have a carb level of around ~1 volumes due to CO2 absorbed during fermentation?

For reference the last couple brews I have cold crashed in the fermenters, pressure transfered from my fermenters to kegs that contain CO2 stones. I then store these close to freezing in the conditioning freezer attached to low pressure CO2. After a couple days/weeks I'll connect the OUT of the keg to the OUT of a clean keg and pressure transfer the fully carbonated beer to the new keg. I have had no issues with this transfer. 1. I don't need as many carb stones and 2. I get to leave an additional amount of trub behind and not worry about kicking it up when moving kegs.

 

[rnm410]

Thermo tables and assumed ideal gas law.

http://www.engineeringtoolbox.com/water-specific-volume-weight-d_661.html

So basically what y'all came to terms here, is to force carbonate...

 

[jddevinn]

Thermo tables and assumed ideal gas law.

http://www.engineeringtoolbox.com/water-specific-volume-weight-d_661.html

So basically what y'all came to terms here, is to force carbonate...

Can't use the thermo tables for CO2. Tables assume that the gas is saturated at the associated temperature and pressure and it isn't.

 

[rnm410]

Can't use the thermo tables for CO2. Tables assume that the gas is saturated at the associated temperature and pressure and it isn't.

I didn't.

 

[jddevinn]

I didn't.

What did you use for CO2 then?

 

[rnm410]

What did you use for CO2 then?

Assumed ideal gas law, PV=mrT.
Used the headspace alone as the system. Gas constant and mass will not change, equated state 1 to state 2to determine pressure with constant volume. For volume "draw" I assumed pressure would remain that of ambient and gas would have to cross the control volume. Just a quick simple dirty calc, theoretical but good enough for guidelines.

If I were concerned about gas draw when crashing in a keg. I would hook up the gas out post, on the tube out or threaded portion zip tie a co2 filled balloon to about the size of two fists. It will not carbonate.

If you crash with 10-14 lbs, you are just carbonating as normal.

I can also comment on headspace and co2 blankets.

 

[Anyhowe]

Thought I would follow up. Added 10 psi to 65 degree 5 gal primary fermentation keg with 2.5 gal of beer. Crashed to 36 degrees for two days before adding gelatin. Plenty of positive pressure remaining in keg.