purging kegs

[slugsly]

I've read that due to diffusion if I pressurize an empty keg 5 times to 15psi I will effectively remove all oxygen. What do other people do?

Also, I have access to an oxygen analyzer so I could do tests.

 

[day_trippr]

I fill the target keg from my Star San reservoir 'til it comes out the PRV. Then I CO2-push it back...

Cheers!

 

[doug293cz]

I've read that due to diffusion if I pressurize an empty keg 5 times to 15psi I will effectively remove all oxygen. What do other people do?

Also, I have access to an oxygen analyzer so I could do tests.

That will do a pretty good job of getting the O2 level down. It's not because of diffusion however. The reduction in O2 (and N2) is strictly due to dilution. The purge pressure affects how many purge cycles you need to get to a particular O2 level. The table and chart below shows how pressure and number of cycles affects the O2 levels. The values are percent of original remaining, not mass of remaining. The mass remaining depends on the headspace volume.





Brew on

 

[IslandLizard]

I've read that due to diffusion if I pressurize an empty keg 5 times to 15psi I will effectively remove all oxygen. What do other people do?

Also, I have access to an oxygen analyzer so I could do tests.

This cost the most CO2 and there's always some residual air left. There was a thread on this a few months ago with graphs and calculations. Use the method below, instead.

I fill the target keg from my Star San reservoir 'til it comes out the PRV. Then I CO2-push it back...

Cheers!

+1^ that's a 100% "liquid" purge with near 0% air left at a cost of only 5 gallons of CO2. The most efficient way.

Even when you fill a 5 gallon keg with 4 gallons of beer (80% fill) and just purge the leftover 1 gallon headspace you're at the breakeven point of doing the 100% "liquid" purge @day_tripper described.

 

[slugsly]

It's hard to do that method when dry hopping.

 

[schematix]

You can also fill it with tap water to the top and push it out with CO2.... if your keg is already clean this will be sufficiently sanitary.

FWIW, this is what i've been doing for a while instead of purging the head space and i've noticed a significant positive difference in the flavor of older beers.

 

[doug293cz]

If you fill with water/StarSan and then purge the liquid with CO2, don't take the lid off the keg to fill with beer. Once you remove the lid, diffusion will kick in and the headspace will pick up air rather quickly. Need to push beer into the keg thru the liquid post with the lid vent open (or a unconnected QD on the gas post if you have no lid vent.)

Video showing rapidity of gas diffusion (why you don't want to open the lid after filling the keg with CO2.)

[ame]https://www.youtube.com/watch?v=_oLPBnhOCjM[/ame]

Brew on

 

[Bellybuster]

to be honest, I've never worried about it. I clean and sanitize my kegs then fill from the bottom and do a few purges of the remaining space. I've had kegs that were full for a year+ and never have I experienced any staling (oxidation).
Firm believer in we as home brewers worry about way too many little things and lose the enjoyment of the big thing....beer

flame away, I have shoulders like a trout, I can handle it

 

[IslandLizard]

It's hard to do that method when dry hopping.

How so? Dry hop in the keg with a muslin bag added after the beer has transferred. Yes, you do need to re-purge the headspace, but the contact time with air is minimal.

You can also fill it with tap water to the top and push it out with CO2.... if your keg is already clean this will be sufficiently sanitary.

FWIW, this is what i've been doing for a while instead of purging the head space and i've noticed a significant positive difference in the flavor of older beers.

I agree, deterring oxidation by pre-purging has a tremendous effect on some beers, like IPAs and above. I always have 5 gallons of Starsan in a bucket, so why not use it? It re-sanitizes the dip tubes and posts all during the same purge.

I don't doubt most drinking water is fine sanitary wise, it's the faucet that bugs me.

 

[ncsuwerewolf]

Drink faster and no worries. I assume the dissolved co2 in my beer formed a blanket to protect it as i rack. Then purging with co2 eliminated the o2 from the head space. That and beer doesnt last long.

 

[doug293cz]

Drink faster and no worries. I assume the dissolved co2 in my beer formed a blanket to protect it as i rack. Then purging with co2 eliminated the o2 from the head space. That and beer doesnt last long.

The CO2 blanket is a myth. See the video in post #7 above.

Brew on

 

[Bellybuster]

The CO2 blanket is a myth. See the video in post #7 above.

Brew on

makes folks feel better though. Just proves my point that we worry about way too many things. tens of thousands of brewers rely on the mythical blanket of CO2 and still make great beer.

 

[SanPancho]

Video showing rapidity of gas diffusion (why you don't want to open the lid after filling the keg with CO2.)

so did anyone else notice that the full mixing took 30 minutes? who in the hell takes thirty minutes to fill the keg? i feel like this is exaggerating the speed which air will mix back into your keg. it happens, obviously. but it seems like a 3 or 4 minute fill up cant let in that much air.

 

[IslandLizard]

so did anyone else notice that the full mixing took 30 minutes? who in the hell takes thirty minutes to fill the keg? i feel like this is exaggerating the speed which air will mix back into your keg. it happens, obviously. but it seems like a 3 or 4 minute fill up cant let in that much air.

When you fill a keg, the surface is in motion as is the gas layer above it. Turbulence ruins a lot of things but keeps us alive.

When you fill a 100% liquid-purged keg, don't remove the lid, fill through the liquid-out post or snake 1/4" OD tubing down the gas post stub to the keg's bottom (gas post and dip tube removed).

 

[SanPancho]

Also, I have access to an oxygen analyzer so I could do tests.

here's an idea that might save alot of co2-- but i dont have an o2 analyzer to test it. you feel like testing this one out?

temperature affects both the density and speed of intermixing for gases. so if co2 is kept in the keg cooler (35F-ish), and run slowly down the liquid post, would that be enough of a temp differential to slow or effectively halt the mixing of the co2 injected and the air in the keg?

in my mind i see a little cloud of cold co2 coming out of the post at the bottom of the keg and slowly starting to rise and push the warmer air out the top of the keg.

3 measurements- the o2 level in keg before purging, the o2 level after about 30 seconds of purging, then again after another 30 seconds of purging.

 

[doug293cz]

so did anyone else notice that the full mixing took 30 minutes? who in the hell takes thirty minutes to fill the keg? i feel like this is exaggerating the speed which air will mix back into your keg. it happens, obviously. but it seems like a 3 or 4 minute fill up cant let in that much air.

That was for Bromine gas (Br2), which has a molecular weight of 159.8. CO2 has a molecular wt of 44, 3.6 times less than Br2, so interdiffuses with air much faster. Did you notice how much faster NO2 interdiffused with air vs. Br2 (2:00 minutes in)? NO2 has a molecular wt of 46, so is much more like CO2 w.r.t. diffusion rates. And, as @IslandLizard notes, the turbulence involved with filling will cause the gases to mix much faster.

Brew on

 

[SanPancho]

nope, didnt watch the whole thing. just noticed the video cuts in the bromine part.

and i get the feeling you and lizard are talking about something else entirely. im not saying purging keg isnt worth it. im saying that the worries about what happens when you open a keg to put in a dry hop bag or for other reasons, in the span of 10-20-30 seconds doesnt seem that perilous for your beer.

since you seem to have specific knowledge of gas chemistry and physics, how about you take a look at my question above for slugsly.

 

[Gavin C]

I fill the target keg from my Star San reservoir 'til it comes out the PRV. Then I CO2-push it back...

Cheers!

+1

no oxygen worth talking about. No analysis needed.

Then I fill it without opening.

 

[doug293cz]

here's an idea that might save alot of co2-- but i dont have an o2 analyzer to test it. you feel like testing this one out?

temperature affects both the density and speed of intermixing for gases. so if co2 is kept in the keg cooler (35F-ish), and run slowly down the liquid post, would that be enough of a temp differential to slow or effectively halt the mixing of the co2 injected and the air in the keg?

in my mind i see a little cloud of cold co2 coming out of the post at the bottom of the keg and slowly starting to rise and push the warmer air out the top of the keg.

3 measurements- the o2 level in keg before purging, the o2 level after about 30 seconds of purging, then again after another 30 seconds of purging.

The gas flow will enhance the mixing, so it will mix faster than by diffusion alone. I doubt it would save gas compared to multiple purges after filling, unless the keg had significantly less than 5 gal in it. You could also never get the O2 level as low as you can with the multiple purge method, without using excessive amounts of CO2. The multiple purge method is deterministic, so you can calculate exactly what the results will be. Trying to purge an open keg by flowing CO2 thru the liquid dip tube is not deterministic, so you will never know what your residual O2 is, without measuring it.

If you want to minimize CO2 usage, then fill with liquid, push the liquid out with CO2, and then transfer using a fully closed system (except for the CO2 vent.)

It's much easier to work with the laws of physics than to try to work against them. That's why you don't push on a rope.

Brew on

 

[schematix]

You can simplify a lot in home brewing and still create a drinkable product.

However, my experience is that most home brew isn't nearly as good as the brewer who made it thinks it is.

 

[Rev2010]

That was for Bromine gas (Br2), which has a molecular weight of 159.8. CO2 has a molecular wt of 44, 3.6 times less than Br2, so interdiffuses with air much faster. Did you notice how much faster NO2 interdiffused with air vs. Br2 (2:00 minutes in)? NO2 has a molecular wt of 46, so is much more like CO2 w.r.t. diffusion rates. And, as @IslandLizard notes, the turbulence involved with filling will cause the gases to mix much faster.

Brew on

So then what about temperature stratification? It's been asked but no one has addressed it. I keep my co2 tank in my kegerator at 36 degrees while my room temp is typically 68-70 degrees. I push sanitizer out of my keg with 5psi then remove the lid, run the tube into the keg and slip it onto my fermenter barb, and open the ball valve. I see a cloudy fog of CO2 on top of the beer the whole fill. And the fill takes only a couple of minutes. If you're saying O2 is mixing in from a warm air temp into a cold bed of CO2 at a fast enough rate to cause oxidation I'm just not detecting it in any of my beers.

I can't for the life of me seeing warm ambient air mixing so quickly with a cold CO2 bed through a small corny keg opening in such rapid speed as to be of concern <shrug>


Rev.

 

[slugsly]

That will do a pretty good job of getting the O2 level down. It's not because of diffusion however. The reduction in O2 (and N2) is strictly due to dilution. The purge pressure affects how many purge cycles you need to get to a particular O2 level. The table and chart below shows how pressure and number of cycles affects the O2 levels. The values are percent of original remaining, not mass of remaining. The mass remaining depends on the headspace volume.

View attachment 323772

View attachment 323773

Brew on

Thanks for posting the charts.


Am I going to notice the difference if I purge 5-10 times instead of pushing sanitizer out of the keg then trying to quickly get a bag in? Maybe not but it's just $0.50 of co2. I'd bet the entire headspace becomes ambient air in 10 seconds of dropping hops in.

 

[schematix]

Thanks for posting the charts.


Am I going to notice the difference if I purge 5-10 times instead of pushing sanitizer out of the keg then trying to quickly get a bag in? Maybe not but it's just $0.50 of co2. I'd bet the entire headspace becomes ambient air in 10 seconds of dropping hops in.

I was ignorant for years that purging was sufficient. After I perfected all of my other processes I still noticed that around a month in the keg the beers started to develop an odd off flavor. Then I read about water purging kegs and how its more effective and uses less CO2.

I'm drinking a Marzen I brewed in August and kegged in September right now and it still tastes great. In fact, brewing another revision of it on Monday to keep the pipeline full.

Another key tip is to make sure your fermenter is sealed well. This is another easy place to accidently introduce O2 that the yeast won't eat. As soon as the beer hits FG it needs to get into a sealed O2 free container. I used to let beers sit 3-4 weeks, but now I try to catch it at 2, 3 weeks at the absolute most. All for the better.

 

[SanPancho]

It's much easier to work with the laws of physics than to try to work against them. That's why you don't push on a rope.

So then what about temperature stratification? It's been asked but no one has addressed it.

exactly. the laws of temperature and pressure ARE physics. its like fighting the laws of physics is bad, but ignoring them is fine?

of course doing what you can to remove oxygen from interacting with beer is good, no one disputes that. but let's be honest- overkill is for reals.

i'd bet the farm that you dont need to remove 100% of the o2 to remove 100% of the detectable effects of o2.

Just proves my point that we worry about way too many things.

You can simplify a lot in home brewing and still create a drinkable product.

trying to find a happy medium between cost/waste/energy on one hand, and efficiency/practicality/simplicity on the other seems reasonable to me. especially when answering the question only takes 60 seconds and fills a keg with co2 that was going to be filled with co2 anyways.

anybody out there got a cold co2 tank and an o2 sensor?

 

[day_trippr]

[...]i'd bet the farm that you dont need to remove 100% of the o2 to remove 100% of the detectable effects of o2. [...]

Not sure anyone would want your farm but companies like Bud measure O2 content down to microliter volumes and do overkill things like triple-purge bottles and cap-on-foam.

So I'm guessing they think even tiny amounts of O2 are worth avoiding...

Cheers!

 

[Rev2010]

Not sure anyone would want your farm but companies like Bud measure O2 content down to microliter volumes and do overkill things like triple-purge bottles and cap-on-foam.

So I'm guessing they think even tiny amounts of O2 are worth avoiding...

Cheers!

And if the homebrewer did all the things Budweiser did for their beers I'm guessing our costs would be unreasonably expensive. Let's not go comparing homebrewer scale to major uber famous uber rich corporations now.


Rev.

 

[Mexibilly]

Fairly new to kegging, but I rack to keg through the top, seal, purge, carb then serve.
My beer tastes great to me and others. Never let a keg age for months, they go sooner than that, but for my purposes what's described here is unnecessary overkill.
If I intend to store and serve long term I'll remember this thread, but certainly wouldn't mess with all that when the kegs go quickly

 

[krackin]

That will do a pretty good job of getting the O2 level down. It's not because of diffusion however. The reduction in O2 (and N2) is strictly due to dilution. The purge pressure affects how many purge cycles you need to get to a particular O2 level. The table and chart below shows how pressure and number of cycles affects the O2 levels. The values are percent of original remaining, not mass of remaining. The mass remaining depends on the headspace volume.

View attachment 323772

View attachment 323773

Brew on

In the olden days we used cherry bombs or silver salutes. Then again, we used those for many of life's issues. I suppose, the use of these as one would aspirin, most likely gave rise to the maddened raving liberals of today.

My fault.

 

[SanPancho]

Not sure anyone would want your farm but companies like Bud measure O2 content down to microliter volumes and do overkill things like triple-purge bottles and cap-on-foam.

So I'm guessing they think even tiny amounts of O2 are worth avoiding...

Cheers!

yes, but why dont YOU have the equipment to measure O2 by the microliter? to beechwood age? to run your own onsite CO2 plant, water quality system, yeast laboratory and chemical analysis center?

maybe because its.....overkill?

or did i miss the part about where you only use imported $5/liter Fiji bottled water to brew your beer because Money Is No Object!?!?!

 

[day_trippr]

See the first reply to the OP's post and you'll see (1) no O2 meter required and (2) the most efficient way to purge a keg.
Nobody was advocating anything, it was a simple answer to a rather simple question.

So, exactly what is your contribution to this thread?

If you don't believe in keeping oxygen out of your brewing practice, that's fine for you.
If you want to claim that oxygen in brewing is a non-issue, that's your problem...

Cheers!