Plastic soda bottle to displace beer in keg with CO2?

[AnchorBock]

Assuming you had a clean empty soda bottle and a carbonator cap of some sort, could you fill the bottle with CO2, then hook up the bottle to a keg (through a regulator of some sort/cask breather) to displace beer that is pulled out via hand pump?

Essentially you'd use the bottle as a CO2 tank only to displace beer that is dispensed so as to not allow air in when dispensing. There would be a disconnect attached to the bottle, the line would go through a cask breather, and back out into the gas in on the keg. Any reason why this wouldn't work? How would I calculate how many PSI at 1 or 2 liters to displace a full 5 gallon keg?

Thanks

 

[MrFoodScientist]

So you're looking to pump in CO2 instead of air? That said, you're essentially using a soda bottle as a CO2 tank?

14.7psi is about 1 volume, so if you're looking to displace a full 5 gallon keg, a 2 liter bottle would need to be pressurized to...

you need 2-2L bottles/gallon and there are 5 gallons so 2x5=10, 10x14.7=147psi.

It doesn't sound like a safe idea idea. I'd recommend you get a paintball tank and dispense that way.

 

[Misplaced_Canuck]

The maximum working pressure of a soda bottle apparently is 100PSI.

You'd have a hard time regulating how much is going from the 2L bottle @ 100 PSI to the keg at say 8 PSI. You'd have to 'burp' the valve to increase the CO2 in the keg.

MC

 

[badbrew]

no. would require 100's of psi to compress enough.

easy

get that little co2 device for that.

 

[KevinM]

I suppose it will help to know what reason's you're looking at doing it this way for. Is it to try to travel with a keg and you don't wish to bring along a co2 tank?
Is it to dispense beer using the english pub style method?

If it's the pub style method (using a handpump/beer engine to pull beer from a naturally carbonated cask), then you can just attach the co2 tank and keep it at some psi where it only replaces the beer and isn't used to dispense it.

If it's just to travel, per mrfoodscientists calculations, of which looks right but I haven't recalced, It appears you would just need several 2 liter bottles (of which each needs its own carbonator cap and would need to be pre-pressurized) and you probably won't get all the co2 out, since the vacuum required probably wouldn't fully collapse the bottle. (It could, but I'm thinking the vacuum required probably wouldn't get to the point of passing the ridigity of certain areas of the bottle.)

 

[JRems]

I don't think the carbonator cap can take 100psi. I remember reading on the package it has a max psi, I think it's closer to 30 psi max

 

[Special Hops]

I don't get what you are trying to do.

But if you are talking about taking a keg and a bunch of 2 liters on a trip with carbonate caps...

Just fill full the 2 liters with beer and pressurize with the carbonator. That way it will save you from transporting the keg.

 

[badbrew]

I don't get what you are trying to do.

But if you are talking about taking a keg and a bunch of 2 liters on a trip with carbonate caps...

Just fill full the 2 liters with beer and pressurize with the carbonator. That way it will save you from transporting the keg.

That is how you road trip.

 

[AnchorBock]

Dispensing ale from a hand pump through a cask breather, basically .25 psi. Want to have the setup on the main floor instead of my basement where the main kegging eqpmt is. The co2 would go in as necessary through the breather as opposed to letting air in.

 

[AnchorBock]

It wouldnt be used to dispense or carbonate, just displace.

 

[JuanMoore]

Dispensing ale from a hand pump through a cask breather, basically .25 psi. Want to have the setup on the main floor instead of my basement where the main kegging eqpmt is. The co2 would go in as necessary through the breather as opposed to letting air in.

How would you keep the pressure from immediately entering the cask? Do you have some sort of pressure regulator rigged up between the 2liter and the cask that can accurately dispense less than 1psi?

 

[KevinM]

Okay, english pub style then. Hmm, can you just run a beer line up from the basement to the beer engine like some sort of pub?

 

[badbrew]

It wouldnt be used to dispense or carbonate, just displace.

If you put co2 back in to replace what is lost when you pour beer out, then it has to be compressed or the co2 in the beer would fall out into the same space making flatter beer.

One thing that you could do is overcarb the beer by 10 psi (instead of 10 make it 20). Then when you pour, make sure it is very cold (33-35) and then every time you pour, the pressure would drop a little but would still be acceptable for a while until it reaches 10 psi. If you wait a few minutes between pours, the headspace would be pressurized enough to pour again by itself with no pumps or plastic bottles needed.

 

[edmanster]

what about a 1 psi check valve and a micro regulator? the pressure in the cask cant reach more than a psi and only excepts co2 in when a vacuume is created.. idk, too many pints maks mii think funny

 

[AnchorBock]

Thanks for the replies - I'm pretty sure this will work, just not sure how many 2 liters full of CO2 at around 30 PSI it will take to displace a full keg. Since I'd only be having 1-2 pints at a time, even if it lasts around a week before I need to bring the 2 liter soda bottle back downstairs to refill it with CO2 from the kegerator I'd be happy. I use pin lock kegs so I'll have to build my own carbonator cap of sorts - maybe it will hold more than 30 PSI. If I end up doing this I'll post some pics and results.

 

[OntarioBeerKegs]

Although DIY is fun and I love a trip to the hardware store. Have you considered just using a keg charger? The hand held units with the 8/12 gram CO2 cartridges? Sounds like a great fit for your intended application.

The plastic carbonation caps are a bad design, the stainless ones are built like tanks though and will not break at 30 PSI. You will pop the regulator safety valves long before have any problems with them.

 

[JuanMoore]

Thanks for the replies - I'm pretty sure this will work, just not sure how many 2 liters full of CO2 at around 30 PSI it will take to displace a full keg. Since I'd only be having 1-2 pints at a time, even if it lasts around a week before I need to bring the 2 liter soda bottle back downstairs to refill it with CO2 from the kegerator I'd be happy. I use pin lock kegs so I'll have to build my own carbonator cap of sorts - maybe it will hold more than 30 PSI. If I end up doing this I'll post some pics and results.

Now that I think about it more, you'd definitely need to use a cask breather. I'm not sure where the crazy math at the start of this thread came from, but a 2L filled to 30psi is more than enough gas to displace a 5 gal keg at your stated 0.25 psi (assuming it's filled at the same temp that both it and the cask will be stored at). The issue IMO is that most breathers require a constant 5 psi being applied to them in order to work properly. This means you'd need to rig a regulator between the 2L and the breather, and since the pressure in the 2L would only be 2.7psi towards the end of the keg, it might not be enough pressure to operate the breather. I'm guessing that the breather will still work as long as it's being supplied with at least a couple psi, but I don't know since I don't have any experience with them myself. You'd need to fill the 2L with 55-60psi to still have 5psi on the breather at the end of the keg.

 

[AnchorBock]

Now that I think about it more, you'd definitely need to use a cask breather. I'm not sure where the crazy math at the start of this thread came from, but a 2L filled to 30psi is more than enough gas to displace a 5 gal keg at your stated 0.25 psi (assuming it's filled at the same temp that both it and the cask will be stored at). The issue IMO is that most breathers require a constant 5 psi being applied to them in order to work properly. This means you'd need to rig a regulator between the 2L and the breather, and since the pressure in the 2L would only be 2.7psi towards the end of the keg, it might not be enough pressure to operate the breather. I'm guessing that the breather will still work as long as it's being supplied with at least a couple psi, but I don't know since I don't have any experience with them myself. You'd need to fill the 2L with 55-60psi to still have 5psi on the breather at the end of the keg.

I was actually planning to use a low pressure propane regulator as a cask breather, its been reported to work fine and works at about .25 psi if i recall correctly. I wouldnt mind having to swap a 2 liter bottle on one keg. Thanks for the info.

 

[JuanMoore]

I was actually planning to use a low pressure propane regulator as a cask breather, its been reported to work fine and works at about .25 psi if i recall correctly. I wouldnt mind having to swap a 2 liter bottle on one keg. Thanks for the info.

That's a bit of a different story. Unlike a cask breather, a regulator will actually put constant pressure on the beer, which means you'll lose quite a bit of gas through absorption. FWIW every low pressure LP regulator I've ever seen puts out 11" WC, which is about 0.5psi. Adding a constant 0.5psi of gas pressure will increase the carbonation by ~0.3 vol, which by my rough calculations would mean a loss of about 11.4 grams of CO2 for 5 gal. That alone would require a 2L filled with CO2 to ~46psi. My guess is that you'd need two and a half 2L bottles filled to 30psi with the set-up you're describing (assuming equal fermentation and serving temps). The first 1.5 bottles will simply be absorbed by the beer over the first ~2 weeks, and then it should take less than a bottle to replace the headspace of the entire keg as the beer is emptied.

If you carbonate your beer to 0.3 vol over the equilibrium level at your serving temp first, then you wouldn't need to worry about the beer absorbing the gas, and would only need one bottle to serve the whole keg. Likewise, if your fermentation temps are a few degrees lower than your serving temp, and you keg and then seal the keg up before raising the temp, the residual carbonation will be high enough that the beer won't absorb any more. If on the other hand your fermentation temps are higher than your serving temps, you're going to lose even more gas to absorption, and would be better off carbing the beer to the appropriate level before kegging it (0.3 vol more than equilibrium level at your serving temp).

What's your planned serving temp, and what are your usual fermentation temps? Is your serving temp pretty stable, or does it fluctuate quite a bit?

 

[AnchorBock]

That's a bit of a different story. Unlike a cask breather, a regulator will actually put constant pressure on the beer, which means you'll lose quite a bit of gas through absorption. FWIW every low pressure LP regulator I've ever seen puts out 11" WC, which is about 0.5psi. Adding a constant 0.5psi of gas pressure will increase the carbonation by ~0.3 vol, which by my rough calculations would mean a loss of about 11.4 grams of CO2 for 5 gal. That alone would require a 2L filled with CO2 to ~46psi. My guess is that you'd need two and a half 2L bottles filled to 30psi with the set-up you're describing (assuming equal fermentation and serving temps). The first 1.5 bottles will simply be absorbed by the beer over the first ~2 weeks, and then it should take less than a bottle to replace the headspace of the entire keg as the beer is emptied.

If you carbonate your beer to 0.3 vol over the equilibrium level at your serving temp first, then you wouldn't need to worry about the beer absorbing the gas, and would only need one bottle to serve the whole keg. Likewise, if your fermentation temps are a few degrees lower than your serving temp, and you keg and then seal the keg up before raising the temp, the residual carbonation will be high enough that the beer won't absorb any more. If on the other hand your fermentation temps are higher than your serving temps, you're going to lose even more gas to absorption, and would be better off carbing the beer to the appropriate level before kegging it (0.3 vol more than equilibrium level at your serving temp).

What's your planned serving temp, and what are your usual fermentation temps? Is your serving temp pretty stable, or does it fluctuate quite a bit?

Thanks for helping me out with this.

I usually ferment the ales I'd have on cask at about 65, they'd carbonate after priming at about 70. My serving temp will be about 50 and should stay stable (haven't built this enclosure yet, but I'll be using a wine fridge cooling unit and a temp controller). Ill be carbonating to 1-1.3 volumes roughly. The liquid line will likely go about 12" or so above the keg to the hand pump. I really would not want the beer to absorb additional CO2 unless I plan for that when priming. A lot of session beers taste pretty harsh with excess CO2.

 

[JuanMoore]

Thanks for helping me out with this.

I usually ferment the ales I'd have on cask at about 65, they'd carbonate after priming at about 70. My serving temp will be about 50 and should stay stable (haven't built this enclosure yet, but I'll be using a wine fridge cooling unit and a temp controller). Ill be carbonating to 1-1.3 volumes roughly. The liquid line will likely go about 12" or so above the keg to the hand pump. I really would not want the beer to absorb additional CO2 unless I plan for that when priming. A lot of session beers taste pretty harsh with excess CO2.

That should work perfectly then. The 0.5 psi at 50F works out to about 1.14 vol, so that's where the carbonation level should eventually settle out, even if you under prime or over prime a little bit. As long as you don't under prime too much, one 2L at 30psi should be enough gas for you.