Vacuum racking to kegs ? Minimizing O2 contact via vacuum ?

[brewman !]

I just bought a vacuum pump for a project I'm working on.

I'm wondering if anyone has tried evacuating the air out of a keg and then using the keg vacuum and maybe some additional pump vacuum to suction beer from the fermentor into the keg.

It would save a lot of CO2 compared to filling a keg with sanitizing solution, then pushing that out with CO2.

It would also allow pressurized flow from the fermentor to the keg without having a pressure rated fermentor.

Foaming might be a problem once the initial beer got into the keg due to the low pressure ? But fermented beer should be very low in CO2, so no foaming should occur.

Thoughts ?

 

[Bilsch]

What kind of keg? A corny will just pull the lid in.

 

[RPh_Guy]

Correct me if I'm wrong, but I am pretty sure a vacuum pump doesn't create a true vacuum, so this won't be effective for removing the oxygen.

Cheers

 

[brewman !]

What kind of keg? A corny will just pull the lid in.

I never thought of that. Hmmm...

Could cover the outside of the lid with plastic to seal it off ? Open the pressure relief so that the lid doesn't see any differential pressure. Close it while still sealed under the plastic ?

 

[brewman !]

Correct me if I'm wrong, but I am pretty sure a vacuum pump doesn't create a true vacuum, so this won't be effective for removing the oxygen.

Cheers

A good vacuum pump does pull a true vacuum. Only a tiny amount of air will remain.

 

[RPh_Guy]

Which one do you have?

 

[RPh_Guy]

If you expose fermented beer to a vacuum you'll have an amazing amount of foam. There is in fact quite a bit of residual carbonation when fermentation completes.

 

[brewman !]

Mastercraft 2 stage.

 

[RPh_Guy]

Mastercraft 2 stage.

Specs on this model:
http://www.mastercraftusa.com/produ...od-Pump-20-gallon-SMP-431001.php#.XZDrLrcpCh8

Says it pulls 84" of water; that's equivalent to only 0.2 atmospheres of pressure, so definitely not a true vacuum.

 

[brewman !]

Mastercool 90066-2V-110

https://www.mastercool.com/product/90066-2v-110/

Pulls 15 microns of vacuum, which is more than 99.99% evacuation.

https://www.engineeringtoolbox.com/vacuum-converter-d_460.html

 

[Vale71]

A true vacuum pump can drop pressure to as low as only a few millibar. One issue it that atmospheric pressure will push in the lid of a corny keg possibly damaging it long before such a vacuum is reached. Foil will rip in a few milliseconds, 1 atmosphere is really a lot of pressure.
If you owned a keg that could take a vacuum without being damaged that would still be hard to do. As you open the valve on your fermenter you'll have full atmospheric pressure pushing on the beer and I've already mentioned that it is really a huge force. As a result beer will transfer at excessive speed and, also due to the vacuum pulling CO2 out of solution, it will foam like crazy. This is not as bad as it sounds as foam will still not be able to get out and neither will fermentation CO2 as the keg will remain sealed throughout and foam will be destroyed by the keg quickly filling up. This will still have effects on head retention though, how severe this will be is hard to tell.
The biggest issue in the end is finding a type of keg that will take a vacuum without imploding in some way...

 

[RPh_Guy]

due to the vacuum pulling CO2 out of solution, it will foam like crazy.

Forgive me here I'm a little rusty with the gas laws.
Suppose the vacuum pulls 0.5 vol CO2 out of the beer, does that mean it will only 50% transfer?

 

[brewman !]

Forgive me here I'm a little rusty with the gas laws.
Suppose the vacuum pulls 0.5 vol CO2 out of the beer, does that mean it will only 50% transfer?

No, because if the keg pressure ever reaches atmoshere pressure, the CO2 will go back into solution.

 

[RPh_Guy]

No, because if the keg pressure ever reaches atmoshere pressure, the CO2 will go back into solution.

It would not go back into solution. Do you carbonate your kegs simply by filling the headspace with CO2? No, it requires time and pressure.

 

[IslandLizard]

I think a vacuum transfer is asking for a lot more work and possibly more problems.

It would save a lot of CO2 compared to filling a keg with sanitizing solution, then pushing that out with CO2.

A lot? It's only 6-8 gallons of CO2 gas per corny keg, if toward the end you drop the pressure to around 5-6 psi. This includes a little extra for purging the first pint of headspace of leftover air under the lid and post domes.

I use probably as much or more CO2 flushing/purging bucket headspaces when adding/stirring dry hops, etc. as by pushing out the Starsan.

 

[Pkrd]

What kind of keg? A corny will just pull the lid in.

And if it doesn't do that it will pull the sides in.

 

[RPh_Guy]

A lot? It's only 6-8 gallons of CO2 gas per corny keg

Alternately, some people purge kegs using fermentation CO2, which requires none from your tank, and is more pure anyway. You can also spund/prime so you don't need CO2 to carbonate.

@brewman !
If we haven't convinced you it's a bag idea to try to transfer into a vacuum keg, at least please take a video of the process for educational purposes.
Cheers

 

[Dland]

I have the gear to try this, and was thinking of running an experiment before posting. But it occurred to me one would also have somehow stop the other poppet from letting air in while developing initial vacuum, and decided it was too much effort for me as I think foaming and seal problems are likely too.

But if you do try this, yes, please post results.

 

[brewman !]

But it occurred to me one would also have somehow stop the other poppet from letting air in while developing initial vacuum

The poppet will be pulled in, thus sealing harder.

 

[Vale71]

Forgive me here I'm a little rusty with the gas laws.
Suppose the vacuum pulls 0.5 vol CO2 out of the beer, does that mean it will only 50% transfer?

I don't think it will have time to pull that much CO2 out of solution. It's really a race condition between how fast beer is pushed in and how fast CO2 comes out of solution.

BTW CO2 will go back into solution, eventually. Beer at end of fermentation is saturated at CO2 partial pressure of approx 1 bar. As CO2 is pulled out of solution it will no longer be saturated. Transfer will stop when headspace pressure equals atmospheric pressure of approx 1 bar but the atmosphere in the headspace will be made of 100% CO2 so total pressure = CO2 partial pressure. Since beer is no longer saturated under such conditions CO2 will start going into solution again, it will just be way too slow for it to be practical as a way of transferring more beer. What you could do in practice is open the PRV while ensuring that the receiving vessel lies lower than the fermenter, so that further transfer will take place by means of gravity. Alternately if your fermenter allows you can apply a slight overpressure with a CO2 regulator and that will keep the transfer going even once vacuum is exhausted. As long as you have a steady outflow of CO2 from the PRV there will be no oxygen ingress. Once the keg is full you stop the transfer by letting go of the PRV so that the vessel is sealed again and no oxygen can enter. It's actually a quite elegant solution if you think about it but the biggest issue is finding a vessel that can hold and withstand a vacuum without being severely damaged.

When you force carb beer you need more than 1 bar of pressure simply because your beer is already saturated for that pressure from fermentation CO2.

 

[Vale71]

The poppet will be pulled in, thus sealing harder.

Poppets seal by pushing out and are released by pushing them in. They have to work like that in order to self-seal under pressure, the higher the pressure, the stronger the seal.

 

[Dland]

^^^I agree, also whole system designed for pressure, not vacuum. I'm sure it could be done, but one would also have to figure a way to prevent post fittings from sucking air under any but the most mild vacuum.

 

[Bobby_M]

You have a hammer and are looking for the nail.

Co2 is cheap. You'd still need to feed co2 into the fermenter to protect from oxygen.

 

[Vale71]

Forgive me here I'm a little rusty with the gas laws.
Suppose the vacuum pulls 0.5 vol CO2 out of the beer, does that mean it will only 50% transfer?

BTW in your hypothetical case you would only transfer 66,6% of the total volume. 0.5 vol means you'll have CO2 with a volume of 0.5 times the volume of the liquid and not of the total volume. This translates to 2/3 of the total volume as liquid, 1/3 as gas at normal conditions.

 

[RPh_Guy]

BTW in your hypothetical case you would only transfer 66,6% of the total volume. 0.5 vol means you'll have CO2 with a volume of 0.5 times the volume of the liquid and not of the total volume. This translates to 2/3 of the total volume as liquid, 1/3 as gas at normal conditions.

I was assuming all of the gas (CO2, and other vapor from boiling) gets pulled into the keg first because that's where the vacuum is, rather than half of it getting released on the atmospheric/open side.
Hypothetically.

 

[Vale71]

Gas cannot be pulled in as you'll be transfering from the bottom of the fermenter. Beer will be pulled in (actually, beer is pushed by atmospheric pressure but the result is the same) and will start foaming strongly due to CO2 release once exposed to vacuum in the keg. If 0.5 vol of CO2 is released as gas the other half (assuming the beer had exactly 1.0 vol of CO2 from fermentation) will just remain in the beer, it's not an "all or nothing" process.

 

[mkosonen]

I use a Jun-Air dental air compressor as a vacuum pump when I transfer from AceRoto fermentors to sankey kegs. I connect the "inlet" of the air compressor (which pulls vacuum) to the gas side of the transfer coupler, and a dip tube in the fermentor to draw the beer into the beer side of the transfer coupler. I always purge the keg with CO2 regarless of how much vacuum the pump draws.

Cheers!
Matt