Negative Pressure in Conical from Cold Crash Vacuum

[Brewmegoodbeer]

Hello all,

In the over 2 years of brewing, I have never put thought into the vacuum that is created when cold crashing until now. I noticed that after cold crashing for about 24 hours, my blow off tube was filled with water almost the the topic of the conical (1/2” 3 ft of tubing). To prevent this in the future i think I might just cap off my conical after fermentation to cold crash. How much negative pressure is accumulated? I see ppl habe done this successfully with glass carboys (dangerous id say) successfully. My conical can take up to 15 psi working pressure but still curious of this negative force. This then creates the problem of the air rushing in when its time to rack into the keg. This is why i put a “gas in” ball lock at the end of the blow off tube and simply take off a carbonation cap to seal off the the conical until im ready to rack which then ill do a closed loop racking procedure. The carbonation cap is on the gas in ball lock in a bucket of star san while fermenting to allow gas to come out. Check out what i mean here:

 

[ajdelange]

I've seen some really heart-rending pictures of what has happened when people have fired up a CIP system and blown caustic into some large (expensive) cylindroconicals witout purging the CO2. Message is that they are better at withstanding pressure than vacuum. The amount of vacuum pulled by cooling is sufficiently well predicted from PV = nRT (don't forget to use Kelvin or Rankine temperature and absolute pressure) and isn't enough to do you a mischeif but don't shoot caustic in there without purging the CO2 first or making sure that a port is open to the air.

The guy in the video has it almost right with respect to racking to a keg from a conical. First comment is that the keg has to be pressurized and depressurized several times with CO2 to get the air out. It is much better (you'll save a lot of gas) to fill the keg with sanitized water (absolutely full) and then push that out with CO2. Then backfill from the fermenter against the residual pressure in the keg. IOW, pressurize the fermenter to a bit above the residual pressure in the keg and use that pressure to force the beer into it displacing the CO2 from the kegs gas port through a needle valve to the ambient. This is conveniently done by making a keg filler from a T, a needle valve and a pressure gauge.

 

[PlinyTheMiddleAged]

Since your conical can take 15 psi, I’d hit it with 15 psi before cold crashing. Then pressurize it again about half way down to your crash temperature.

Better yet, set your regulator to 5 psi and keep CO2 hooked up until you reach your cold crash temperature.

 

[Brewmegoodbeer]

Since your conical can take 15 psi, I’d hit it with 15 psi before cold crashing. Then pressurize it again about half way down to your crash temperature.

Better yet, set your regulator to 5 psi and keep CO2 hooked up until you reach your cold crash temperature.

Ive done alot of research on this over the past 48 hours or so and it seems your suggestion aligns with what I found on other forums what best works to counteract the cold crash vacuum. I found this forum where the owner of bainbridge brewing co. Puts 5 psi on the headspace, caps the fermenter and cold crashes.
http://discussions.probrewer.com/showthread.php?59591-Cold-crashing-and-blow-off-tubes
The 5 psi supposedly counteracts the vacuum and keeps positive pressure in the vessel. Im trying this out on my next batch. I recently ordered a triclamp gas post that ill be able to use to put 5 psi on the fermenter with.

 

[day_trippr]

You don't actually need anywhere close to 5 psi, just positive CO2 pressure is enough.
fwiw, I've been doing a much lighter version of cold-crashing-under-CO2 (~ 0.4 psi) for the last year+ and believe it has extended the shelf life of my more fragile beers. It certainly removes any concern about suck-back

Cheers!

 

[ajdelange]

As noted earlier, the reduction in pressure from a cold crash from room temperature (20 °C = 293K) to freezing (0 °C = 273 K) results in a 7% reduction in pressure (273/293 = 0.931741) which is not something you need to lose sleep over. If, for example, you spund at 1 atmosphere (100 kPa gauge, 200 kPa abs) at room temperature at the end of the crash the pressure will be 186 kPa absolute or 86 kPa gauge (from 14.7 pisg to 12.6 psig). If you spunded at 5 psig pressure would drop to 3.6 psig. This does not mean that you shouldn't pressurize after spunding. You definitely should but that is more to make up for gas leaking out during conditioning (so that you will have enough for counter pressure filling) than it is to compensate for the 'vacuum' produced by crashing.

My own procedure, as another example of what people do, is to close the spunding valve when CO2 evolution slows to about 2 blurps per minute and check fermenter pressure daily after that. It will continue to rise for a while and when it starts declining the fermentation is complete to the point that the CO2 evolution is less than the system leakage. At that point I put on 15 psig CO2 and start the slide towards freezing (I don't crash - you get better beer if you don't). The CO2 stays on at that pressure until all the beer has been pushed into kegs.

 

[Smellyglove]

As noted earlier, the reduction in pressure from a cold crash from room temperature (20 °C = 293K) to freezing (0 °C = 273 K) results in a 7% reduction in pressure (273/293 = 0.931741) which is not something you need to lose sleep over. If, for example, you spund at 1 atmosphere (100 kPa gauge, 200 kPa abs) at room temperature at the end of the crash the pressure will be 186 kPa absolute or 86 kPa gauge (from 14.7 pisg to 12.6 psig). If you spunded at 5 psig pressure would drop to 3.6 psig. This does not mean that you shouldn't pressurize after spunding. You definitely should but that is more to make up for gas leaking out during conditioning (so that you will have enough for counter pressure filling) than it is to compensate for the 'vacuum' produced by crashing.

My own procedure, as another example of what people do, is to close the spunding valve when CO2 evolution slows to about 2 blurps per minute and check fermenter pressure daily after that. It will continue to rise for a while and when it starts declining the fermentation is complete to the point that the CO2 evolution is less than the system leakage. At that point I put on 15 psig CO2 and start the slide towards freezing (I don't crash - you get better beer if you don't). The CO2 stays on at that pressure until all the beer has been pushed into kegs.

Sorry this is off topic, but relevant to me at this point. You write system leakage of co2 as it's something normal. Is it? I have a spunding valve with hookup (hose and ball lock) which leaks a bit and I can't get it sealed.

 

[ajdelange]

I don't really know if it is normal but I have 2 fermenters both of which exhibit it (one more than the other). There doesn't seem to be any liquid leakage (no beer on the floor) but CO2 does sneak out. The fermenters have automatic pressure relief valves and vacuum breakers (so I'll never post a heart rending picture) and I'll put my money on those (in particular the pressure relief) as the source of the gas leaks.

I don't see this question as being off topic.

 

[logdrum]

You don't actually need anywhere close to 5 psi, just positive CO2 pressure is enough.
fwiw, I've been doing a much lighter version of cold-crashing-under-CO2 (~ 0.4 psi) for the last year+ and believe it has extended the shelf life of my more fragile beers. It certainly removes any concern about suck-back

Cheers!

Could you elaborate on this”lighter version” process?

 

[day_trippr]

Could you elaborate on this”lighter version” process?

"Lighter version" as in only using ~ 0.4psi vs the 5 psi mentioned above my reply.
I use a Marshall dual-stage fixed 11" WC regulator to provide the CO2 "top pressure" to my carboys (the reason why I use very light pressure).

I use the balloons as "pneumatic fuses" in case something goes utterly pear shaped. They blow before the glass does (I've tested it a few times )
I slap them on once the beer has hit terminal gravity, pop them off for a moment to dry hop, and cold crash with them in place...

Cheers!

 

[logdrum]

Thanks!

 

[Augusto Sotero]

As noted earlier, the reduction in pressure from a cold crash from room temperature (20 °C = 293K) to freezing (0 °C = 273 K) results in a 7% reduction in pressure (273/293 = 0.931741) which is not something you need to lose sleep over. If, for example, you spund at 1 atmosphere (100 kPa gauge, 200 kPa abs) at room temperature at the end of the crash the pressure will be 186 kPa absolute or 86 kPa gauge (from 14.7 pisg to 12.6 psig). If you spunded at 5 psig pressure would drop to 3.6 psig. This does not mean that you shouldn't pressurize after spunding. You definitely should but that is more to make up for gas leaking out during conditioning (so that you will have enough for counter pressure filling) than it is to compensate for the 'vacuum' produced by crashing.

My own procedure, as another example of what people do, is to close the spunding valve when CO2 evolution slows to about 2 blurps per minute and check fermenter pressure daily after that. It will continue to rise for a while and when it starts declining the fermentation is complete to the point that the CO2 evolution is less than the system leakage. At that point I put on 15 psig CO2 and start the slide towards freezing (I don't crash - you get better beer if you don't). The CO2 stays on at that pressure until all the beer has been pushed into kegs.

One thing that I just cannot figure out is if the temperature at which the water freezes changes with this change in pressure. Anyone know how to respond to this?

I am a bit worried if at this minor pressure (vacuum) that occurs inside my bucket (of about 0.9atm as shown by AJ) my beer would freeze at a higher temperature. Higher than 0C I mean.

 

[Vale71]

Beer won't freeze at 0°C. As it's a mixture of water, alcool and residual sugars it will freeze at a temperature that already falls below -2°C, depending on actual composition. Positive pressure will actually reduce this temperature (part of the anomalous behaviour of water) even farther, so you definitely don't have to worry about your beer freezing at 0°C.

Edit: sorry, didn't read your question thoroughly. As ajdelange said, as the amount of vacuum your fermenter could experience is very limited any change in freezing temperature will be minuscule.

 

[ajdelange]

Yes, the freezing point of water does increase as you lower the pressure but the change is miniscule. At atmospheric pressure (101.325 kPa) the freezing point of pure water is 0 °C. If you lower the pressure all the way down to 0.611657 kPa the "freezing point" (in quotes because it's also the boiling point i.e. this is the triple point) only increases to 0.01 °C. Thus you need have no concerns that your beer will freeze from this small lowering of pressure.

 

[Augusto Sotero]

Yes, the freezing point of water does increase as you lower the pressure but the change is miniscule. At atmospheric pressure (101.325 kPa) the freezing point of pure water is 0 °C. If you lower the pressure all the way down to 0.611657 kPa the "freezing point" (in quotes because it's also the boiling point i.e. this is the triple point) only increases to 0.01 °C. Thus you need have no concerns that your beer will freeze from this small lowering of pressure.

Problem solved!

Thanks AJ =)