Purging kegs

[scogan]

Before doing some extra dry hopping of some beer that was already conditioned I purged a keg recently by connecting it to my co2 bottle at 12psi and pulling the prv for a second or two twenty times.Hop aroma was tremendous , for about 3 days then pretty much disappeared.So ,the obvious culprit is oxidation,is there some adjustments to purging I should make ? Can`t do the displacing starsan routine because there are dry hops in the keg .Can`t remember what I did with jumper line, but I now fill them with beer first.

 

[VikeMan]

When purging with a CO2 cylinder, you pressurize the keg, then shut off the gas, then release all of the keg's pressure (not a second or two). Turn the gas back on and repeat the whole thing "X" times. Here's a chart that might be helpful.

 

[day_trippr]

Neat table! Can one relate the actual volume of CO2 used (presumably at STP) for each column?

Cheers!

 

[Bobby_M]

Just fill the keg with sanitizer and push it all out with co2. No chart for that.

 

[NSMikeD]

Just fill the keg with sanitizer and push it all out with co2. No chart for that.

He’s dry hopping in the keg.

 

[doug293cz]

One option, if you already have hops in the receiving keg, is to purge with fermentation CO2. It's even better than purging with bottled CO2.

Brew on

 

[Ozarks Mountain Brewery]

every time I keg I purge at least 4 times in an hour, no need to disconnect just pull the relief valve

 

[doug293cz]

every time I keg I purge at least 4 times in an hour, no need to disconnect just pull the relief valve

Four purges will leave way too much residual O2 for an oxidation sensitive beer. See the chart in this post.

Brew on

 

[Ozarks Mountain Brewery]

well I said at least, most times more

 

[day_trippr]

Just fill the keg with sanitizer and push it all out with co2. No chart for that.

Of course. And I do that if for some reason my "fermentation purge" doesn't work out (like when "peak krausen" choked the gas line that one time) but it would be useful if the real CO2 cost could be calculated for comparative purposes...

well I said at least, most times more

The chart clearly indicates it'd take five times more. Don't do that

Cheers!

 

[scogan]

Don’t know if this is overly complicated but I am thinking .Fill keg 3/4 full with starsan and slosh it about , then attach hops up near lid using magnet.Push starsan out,then flush keg 4 times using Vikeman’s method in #2 .

 

[Grizwold1]

If I were to connect the co2 outflow from a 4.5 gal fermentation (c. 1.160 OG) to an empty/sealed corny keg liquid out, then the gas in to a jar of starsan would that produce enough to purge the serve keg sufficiently?

 

[doug293cz]

If I were to connect the co2 outflow from a 4.5 gal fermentation (c. 1.160 OG) to an empty/sealed corny keg liquid out, then the gas in to a jar of starsan would that produce enough to purge the serve keg sufficiently?

doug293cz's epic post on CO2 generation

Brew on

 

[RCope]

Don’t know if this is overly complicated but I am thinking .Fill keg 3/4 full with starsan and slosh it about , then attach hops up near lid using magnet.Push starsan out,then flush keg 4 times using Vikeman’s method in #2 .

If I remember correctly from previous discussions, the amount of headspace doesn't change the required number of purges, it just uses a lot less CO2 if there is a smaller headspace. So, depending on whether you can accept 0 ppm or 0 ppb, the number of purges at 30 psi would be 12 or 18, respectively. Cheers!

 

[scogan]

If I remember correctly from previous discussions, the amount of headspace doesn't change the required number of purges, it just uses a lot less CO2 if there is a smaller headspace. So, depending on whether you can accept 0 ppm or 0 ppb, the number of purges at 30 psi would be 12 or 18, respectively. Cheers

If I remember correctly from previous discussions, the amount of headspace doesn't change the required number of purges, it just uses a lot less CO2 if there is a smaller headspace. So, depending on whether you can accept 0 ppm or 0 ppb, the number of purges at 30 psi would be 12 or 18, respectively. Cheers!

Surely if you 3/4 fill the keg with starsan then push that out you begin with only 5L of air instead of 20L ?However looking at doug293cz’s table you could reach that point in just a couple of purges at 15 psi.

 

[SonomaBrewer]

Just fill the keg with sanitizer and push it all out with co2. No chart for that.

This approach is best, but doesn't work for me. It always leaves a cup or so of sanitizer left in the Torpedo kegs that I use.

Or maybe I am just overly sensitive to the taste of Starsan?

 

[Bassman2003]

When I did the liquid purge method I would raise the PSI at the very end of the liquid so you have about 10 PSI at the end. Then take the gas off, turn the keg over and grab an extra QD. While the keg is turned upside down, put the QD on. This will blow the last bits of Star-san out. Just make sure you pop it off before the gas runs out. It only takes a second. (You need a finely trimmed inner post bit so the liquid can all exit from the gas out.)

 

[TLaffey]

This approach is best, but doesn't work for me. It always leaves a cup or so of sanitizer left in the Torpedo kegs that I use.
Or maybe I am just overly sensitive to the taste of Starsan?

To get that last bit of starsan out:
1. before filling, trim the gas-in post very short
2. after purging, pressurize the keg (some), invert it, and let some gas out through the (short) gas-in post.

I ususally use an adjustable pressure relief valve (my spunding valve) to ensure I don't let out more CO2 than needed to push out the last of the sanitizer, but it can be don with other means. Just don't let the keg become completely depressurized.

 

[day_trippr]

before filling, trim the gas-in post very short

A good idea even if it's not needed for draining purge liquid. Provides extra margin against over-filling

fwiw, all of my kegs have full length Out diptubes and the ends are nestled in the keg wells provided. I have tested two different keg styles, one with the typical bend that puts the tip in the center of the keg bottom, and the other style with the straight diptube that ends in a side well. Either type leaves a tablespoon or less of liquid behind. I can live with that

Cheers!

 

[Cherokee6]

One option, if you already have hops in the receiving keg, is to purge with fermentation CO2. It's even better than purging with bottled CO2.

Brew on

doug293cz - I have been purging my kegs using this method for awhile now. I have not tried hops yet in the receiving keg. Assuming that you place the hops in the keg and then connect to your fermenter to purge with fermented CO2, should there be an expected impact on the hop character with those hops sitting through the purge cycle? (5-7 days of fermentation)?

 

[doug293cz]

doug293cz - I have been purging my kegs using this method for awhile now. I have not tried hops yet in the receiving keg. Assuming that you place the hops in the keg and then connect to your fermenter to purge with fermented CO2, should there be an expected impact on the hop character with those hops sitting through the purge cycle? (5-7 days of fermentation)?

Seems likely that you would lose some fraction of the most volatile hop compounds, but the only way to tell would be by experimentation. Could likely make up the difference by adding a bit more hops. Methods to avoid this loss, and still keep a completely closed system would add more equipment, cost, and complexity (something like a valved auxiliary chamber on the fermenter, that could be purged independently, with less loss of hop compounds.)

For experimental purposes, you would have to do two identical batches, where one used your current dry hop method, and the other placing the hops in the keg being purged. Then evaluate for initial flavor differences, and track the degradation of hop flavor over time for each beer.

Brew on

 

[Cherokee6]

Adding equipment, cost, and complexity are things I am trying to avoid - they go against the age old adage of "keep it simple". I'll try the hops in the purged keg to evaluate cold side oxidation first, and if I get good results from that, I will move on to evaluating the correct amount of hops needed for that method.

Thanks for the quick response!

 

[sibelman]

fwiw, I've gotten fine results with this method even though the hops are in non-ideal circumstances during fermentation. It avoids the various challenges of dry hopping in the fermenter. The only method I've tried that produces stronger aroma/flavor results is my recent experiment using a Randall.

 

[doug293cz]

fwiw, I've gotten fine results with this method even though the hops are in non-ideal circumstances during fermentation. It avoids the various challenges of dry hopping in the fermenter. The only method I've tried that produces stronger aroma/flavor results is my recent experiment using a Randall.

Do you have a link to your randall experiment(s)?

Brew on

 

[sibelman]

link

https://www.homebrewtalk.com/thread...acks-and-best-practices.700861/#post-10308593

 

[Langerz]

When purging with a CO2 cylinder, you pressurize the keg, then shut off the gas, then release all of the keg's pressure (not a second or two). Turn the gas back on and repeat the whole thing "X" times. Here's a chart that might be helpful.

View attachment 814096

This is a great table. Thanks for posting. I'm curious about the reasoning behind shutting off the gas through. I'm sure it uses more CO2, but would the purge be less effective?

 

[Langerz]

Another question popped into my head somewhat related to the OP question.

I've seen a lot of information on ppm and getting that to zero, but I haven't seen a lot about the time exposed. That also has to matter right?

Specifically thinking about OPs dry hop question my standard has been to 1) purge the keg by pushing out star san with CO2 2) open the lid with CO2 flowing in and dump in my hops. Try to be as quick as possible (which usually means messing something up lol). 3) purge a few times - I'm not very exact here, but certainly not getting down to 0 ppm 4) fill the keg 5) do more purge cycles with the limited head space.

I haven't been very precise on the number of purges (process improvement opportunity), but curious if for example you had the keg purged to 200 ppm with only the hops in the keg and during filling and then once the keg was full you purged down to 0 ppm would there be a significant difference. I get there isn't really a process difference either way other than using more/less CO2.

I also understand that during filling the beer is somewhat agitated (I fill through a floating dip tube) so it would absorb more oxygen then if still.

I just upgraded to a conical and dry hopper so I guess it doesn't matter as much to me anymore, but still have a curious mind.


Also one more question again tying back to OPs question the chart starts from normal atmospheric conditions. If OP is starting out with a keg that is fully purged with a star san push and then opens the lid just enough to throw in some hops, he's likely well below the 20.95% O2 content shown right?


Final note - I'm fully aware I'm typing all of this to probably save 50 cents worth of CO2.

 

[Bassman2003]

Exposure time to the open keg does play a factor. The shorter the time the lid is open the less gas that will exchange. How much is tough to know as it seems the process happens fairly quickly. but you do what you can within your process choices.

 

[VikeMan]

This is a great table. Thanks for posting. I'm curious about the reasoning behind shutting off the gas through. I'm sure it uses more CO2, but would the purge be less effective?

I dont think it would be less effective, but it would be wasteful, as you surmised.

I've seen a lot of information on ppm and getting that to zero, but I haven't seen a lot about the time exposed. That also has to matter right?

Yes, the "open" time (and size of the opening, turbulence, etc.) prior to purging has an impact on the amount of gas exchange between the headspace and the atmosphere. And the table does assume starting with a headspace filled with plain old air, at one atmosphere.

Final note - I'm fully aware I'm typing all of this to probably save 50 cents worth of CO2.

The table is useful as a "worst case" scenario. Depending on what you are purging, you can certainly do less, but there's no practical way to know where you'll end up.

 

[Unicorn_Platypus]

I purge all my kegs with sanitizer and occasionally add things like oak or dry hops to the purged keg by opening the lid.

I use floating diptubes in all my keg. This wouldn't work as well with a traditional diptube. I recommend having an in line check valve on your gas line for this to prevent any liquid blowing back into the CO2 regulator

Before making additions to the keg & opening the lid, I attach the CO2 tank gas line to the liquid post (you will need to hookup a black liquid QD to your regulator). This way when I open the lid CO2 is pushing from the bottom up. I use about 12 PSI of pressure when doing this and open / close the lid very quickly for the addition. I pull the PRV & hold it open when opening the lid of course so it doesn't explode in my face at 12 PSI. After sealing the keg back up I hit it with a few purges, and I also purge the headspace a few times after the closed transfer

In terms of residual sanitizer, I have cut gas diptubes so it's easy for me to blow out the extra sanitizer. I use a scale when transferring and am careful not to overfill. I also add 2g SMB to the saniclean solution I use in the purge so that any residual sanitizer won't contain any DO

 

[Unicorn_Platypus]

When purging with a CO2 cylinder, you pressurize the keg, then shut off the gas, then release all of the keg's pressure (not a second or two). Turn the gas back on and repeat the whole thing "X" times. Here's a chart that might be helpful.

View attachment 814096

Great table!

 

[Unicorn_Platypus]

Another thing I find beneficial is adding dextrose & ascorbic when dry hopping to scrub any O2 introduced. 5g ascorbic acid & 12g dextrose does the trick

I also like to naturally carbonate all my kegs with priming sugar instead of force carbonation. This further mitigates any oxygen introduced as the yeast will consume it.

For adding the priming sugar, I use a 500mg syringe and inject to the purged keg via the gas post. See picture attached. Virtually no air is introduced as I ensure to push it out of the line before hooking up to the keg.

My beers stay hoppy & bright for many months.

Also, if you have silicone O rings get rid of them and replace with EPDM or Buna N or the new kegland low2 ones. This helps further protect the shelf life as these materials are less permeable to O2