Vacuum on corny keg

Has anyone ever tried to rack their leg by first starting a vacuum on their keg then attaching the cane? I was thinking this would help with purging the airspace inside the keg as well as speeding up the transfer.

Thoughts? Experiences?

I use a vacuum pump to transfer from fermenter to keg. I connect an ss racking cane to the liquid post and the vacuum pump to the gas post. Works great sofar.

I have also read about the people that use c02 from one vessel to another. Was wondering in both cases if you got much more (or less) sediment when you transfer. I slowly lower the racking cane as the liquid goes down to keep out of the sediment as much as possible. When you do your vacuum transfer is there much sediment and how does the liquid post handle any sediment?

Right now i rack with CO2. I purge my kegs, then connect a SS racking cane to the liquid side, dip it about halfway down the fermenter. Then apply low co2 pressure to the ferm. I get a very clear transfer in about 8 mins.

What i was thinking to do instead is to draw a vacuum on the keg, then fill with co2, then draw another vacuum on the keg. Then submerge the racking cane, and when connected to the liquid post, a siphon would start right away. Idea here being that the keg is purged of oxygen to a very high degree and the vacuum would accelerate the speed of the siphon, at least part of the time.

Few issues i see:
1. Not sure how much vacuum pressure a keg can handle
2. will the co2 dissolved in the beer come out of solution from the vacuum leading to foaming?
3. o2 exposure as o2 is drawn into the fermenter (although contact time is minimal).

I wouldn't pull more than about 2 psi negative pressure on a corny. They are pressure rated, not vacuum rated. If you have one that you are going to scrap anyway, might be a good experiment to find out how much negative pressure they will take before they start to collapse.

Small vacuums won't remove enough O2 to protect from oxidation. So, don't use that as a justification.

Brew on

schematix said:

Right now i rack with CO2. I purge my kegs, then connect a SS racking cane to the liquid side, dip it about halfway down the fermenter. Then apply low co2 pressure to the ferm. I get a very clear transfer in about 8 mins.

What i was thinking to do instead is to draw a vacuum on the keg, then fill with co2, then draw another vacuum on the keg. Then submerge the racking cane, and when connected to the liquid post, a siphon would start right away. Idea here being that the keg is purged of oxygen to a very high degree and the vacuum would accelerate the speed of the siphon, at least part of the time.

Few issues i see:
1. Not sure how much vacuum pressure a keg can handle
I don't know how much a keg can handle but a couple times I have forgot to pull the thermwell out of my conical causing my pump to make negative pressure in the keg. I haven't collapsed a keg yet.
2. will the co2 dissolved in the beer come out of solution from the vacuum leading to foaming?
I never had issues with foaming transferring this way.
3. o2 exposure as o2 is drawn into the fermenter (although contact time is minimal).
Yes you are drawing in o2 as you transfer out but the transfer happens quickly so the exposure time isn't worth worrying about. I have been doing this for 2 years and have never had a batch oxidize. I also purge the keg with co2 to seat the lid then vacuum pump that pressure out before connecting the liquid post.

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I'm thinking about trying this. I made a vacuum/catch can with a couple of hose barbs and a vacuum gauge on a canning jar. It looks like my little 12v DC pump can pull about 4 inHg vacuum on my keg, which is the equivalent of about about 2 psi.

I have a question about something said here though.

Small vacuums won't remove enough O2 to protect from oxidation. So, don't use that as a justification.

Click to expand...

Umm, this seems wrong to me, even a minuscule vacuum pressure would indicate that all gas has been removed from the vessel wouldn't it? How else would the vacuum pressure be created? The vessel must be void of gas.

I think a vacuum isn't simply a flow of gas from higher pressure to lower, it is an actual void regardless of the intensity of the vacuum. When I first hook up my pump there is no vacuum indicated on the gauge. I have to wait several minutes as the gas is removed from the keg, then the vacuum pressure builds.

If there is something I'm not understanding then I can do my usual routine of filling with star-san and then pushing it all out with CO2 to ensure there is no O2 in the keg, but that seems unnecessary if I'm going to pull a vacuum on the keg before I start transferring.

So I tested the vacuum pump on an empty keg. The next step is to test racking 5 gal of water under vacuum a couple of times.

So, you'd need to go back to some gen Chem for this answer. Specifically the gas laws. By removing a small portion of gas (slight vacuum) you're only removing some of the oxygen and you're still left with a 21% oxygen mix in the keg. No matter how long you pull on it you'd have the equivalent mass of o2 in a 5 gal keg at 12psia in the same ratio as air. (You can find the grams using the ideal gas law and .21 o2 mole ratio)

The only way to remove the oxygen sufficiently is to dilute it with co2. And repeat the process. Which is what you're doing when you pressurize and purge with co2. You'd have to pull vacuum and repressurize using co2 many times. Far more times than increasing pressure with co2 up to 30psig.

Think of it this way. When you pull vacuum you're changing the amount of gas in the keg by only:
initial amount of gas - 12.7/14.7 * the initial amount of gas (assuming a 2psi drop)
if you then fill with co2 you've only diluted the o2 slightly by replacing the o2 and n2 lost with co2. On the other hand by raising the pressure to 30 psig you now have an increase in gas in the keg of 47.7/14.7 and that's all co2. I don't feel like getting into numbers but you can see that the dilution of oxygen happens pretty rapidly by increasing the headspace to 30 psig and purging.

I understand the basic idea that only removing a portion of the gas would still leave some oxygen in the keg.

http://hydraulicspneumatics.com/200/TechZone/Vacuum/Article/False/6460/TechZone-Vacuum

That article explains that a vacuum gauge is just measuring the pressure differential and you'd need to see almost 30 inHg for a true vacuum, so you guys are correct.

Now I know that I should do my usual routine of filling the keg with star san and pushing it out with CO2 to purge the keg of O2 before racking to the keg under vacuum.

Thanks!

Thanks for resurrecting a necro thread, FruityHops.

My process has evolved dramatically since i first posted about this almost a year and a half now. Now i ferment in corny kegs, under a little bit of pressure. Too much to post here, but it is closed loop and doesn't require any external CO2 or a racking cane!

As far as removing O2, i've been doing LoDO for almost a year now. I purge my kegs of O2 by completely filing with water, then pushing it all out with canister CO2. I've shortened all my gas dip tubes to be flush on the inside and i fill the keg completely via the liquid post and purge from the PRV, then the gas port while the keg is tilted 45 degrees with the gas port up. Sounds like a lot but its easy.

FYI, vaccum just means a lower pressure relative to something else, because there are fewer gas molecules to exert the force. Practically impossible to have 0 pressure because its nearly impossible to remove all gas, even from space.