purging kegs

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slugsly

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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.
 

doug293cz

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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.

Purge Percent of Original O2 Table.png

Purge Percent of Original O2.png

Brew on :mug:
 

IslandLizard

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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.
 
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schematix

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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

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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 :mug:
 

Bellybuster

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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

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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

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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

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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.

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Bellybuster

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

Brew on :mug:
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

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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

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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

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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

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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 :mug:
 

SanPancho

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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.
 

doug293cz

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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 :mug:
 

schematix

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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

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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 :mug:
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.
 
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slugsly

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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 :mug:
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

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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

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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

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[...]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

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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

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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

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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 :mug:
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

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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

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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!
 

doug293cz

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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.
Taking the lid off/out of the keg causes air currents that will accelerate mixing relative to diffusion alone. Inserting a tube into the keg thru the lid will accelerate mixing. Just how much will depend on exactly how the operation are done. Problem is, there is no way to know how much O2 gets into the keg because of this.

Temperature stratification occurs because heat flow into/out of a system varies from location to location. Without non-uniform heat flow, diffusion would insure uniform temperature throughout. Having a situation where stratification exists would probably slow down the rate of homogenization, if diffusion were the only factor in play.

The fog you see above the liquid is water droplet fog. CO2 gas is invisible, as are all of the other gases that are in the headspace. There are no liquid CO2 droplets possible within the pressure and temperature ranges that can exist for an open keg.

If you open a keg after liquid purging, you will have some level of O2 in the keg, but have no way to determine just how much, unless you actually measure it. O2 analyzers that are accurate down to the ppm level are pretty expensive. For the cost of a little time and CO2, you can be sure of your O2 content without having to buy a meter.

There are two places you need to worry about O2.
  1. O2 absorbed into the beer, primarily due to agitation of the beer in the presence of O2 gas
  2. O2 in the headspace above the beer, which will slowly absorb into the beer
With time both will cause oxidation products to form in the beer. The more total O2, the more total oxidation products will eventually form in the beer. Whether you ever taste it depends on the age of the beer, the total O2 available when packaged, and the sensitivity of your palate to oxidation products.

You have to decide for yourself how much effort you want to expend to minimize the extent of oxidation. There are methods that allow you to know the worst case amount of O2 that you allow in your packaged beer (described earlier in this thread), and there are methods for which you can only guess. Again, you have to decide which type of method you want to use. Personally, I favor the use of deterministic methods.

I am now done with this thread. I provided a factual response in my first reply, and am not particularly interested in a continuing debate about "how much is too much" unless someone has some quantitative data to share.

Brew on :mug:
 

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For a given headspace, which method uses less CO2? Purging more times at lower pressure, or purging fewer times at higher pressure?
 

Rev2010

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For a given headspace, which method uses less CO2? Purging more times at lower pressure, or purging fewer times at higher pressure?
The charts on the first page seem to show twice the amount of purges at lower psi's are more efficient than half the amount of purges at twice the psi. Like looking at purging 4x with 10psi is more efficient than purging at 20psi two times.


Rev.
 

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My method of overkill:

I keep a keg of StarSan at all times, as well as a bucket. I fill most of the way from a bucket, then push the rest of the StarSan in with CO2 pressure. I fill with StarSan until it comes out the release valve. Then I tilt the keg upside down, so the pocket of air that sill remains is at the bottom of the keg, then tilt it back upright at an angle, with the gas-in tube at the uppermost point. So, the air bubble is there. Then, with a bit of pressure, I continue to push StarSan in the liquid-out tube while I unscrew the gas-in post. Once off, the last little bubble of air will be pushed out and StarSan will flow out; I put the post back on to stop the flow. Then, push it all out with CO2, and push beer back in with CO2.

It's decidedly more effort than the average Joe will put in, but it really is pretty quick and easy.

For dry hopping, I do this, then open the keg to drop pellets in as quickly as possible. Then I'll do multiple purges to dilute the O2 that diffused in while opening.

I do this for all beers, but I really pinned this down as the nail in the coffin for hitting IPAs out if the park. My IPAs were always good, great in my opinion. Still, the taste after force carbing was never as out of this world as the final gravity samples tasted. I'm confident it's because if there's any small fraction of O2 present when force carbing, that's essentially force oxygenated immediately. Now, my IPAs taste as nice after a month as they do out of the fermentor.

That's just what I do. I'm sure haters gunna hate.
 
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slugsly

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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!?!?!
CO2 must cost a lot where you live if the expense is comparable to importing water at $5 a litre.

Per the chart posted how is it overkill to purge your keg 5 times to reduce O2? It's practically free.
 

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Another question I have is: how quickly do the oxidation products form?

For example, if I rack from my FV into a keg filled with air (and dry-hops) (taking 5-10 min), then purge the remaining headspace down to <1% O2, will enough oxidation products form to be detectable by taste? Is 5-10 min of exposure to air enough to change the taste? Would the amount of oxidation products be appreciably less if I racked into a CO2-purged keg (using TAK's or day_trippr's method), but then opened the keg to add the dry-hops followed by purging?
 

SanPancho

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CO2 must cost a lot where you live if the expense is comparable to importing water at $5 a litre.

Per the chart posted how is it overkill to purge your keg 5 times to reduce O2? It's practically free.
you dont bother to read the quote. microliter o2 sensors, yeast labs, co2 plants, etc are what i state is overkill. for a homebrewer. and for that matter, any brewery that produces less than 50k bbl a year i'd guess. the cost is enormous.

purging kegs 5 times? i say overkill, you say tomato. read my other statement- it doesnt take a 100% removal of o2 to remove 100% of the detectable effects of o2. which means there is a diminshing return to scale on this process. i can tell you with 100% certainty from a veteran AB brewer that they do not remove EVERY SINGLE MOLECULE of o2 that they can. at some point, its just not worth it. Which is my entire point.

at its heart, this says that there is a limit to the what the human palate can sense, so unless you need 100% o2 removal for some sort of philosophical reason, its overkill- practically speaking, and in the case of AB- professionally speaking.

nobody is claiming that removing o2 from beer is bad- what i'm saying, repeatedly, without anyone actually paying attention- is that there is a point where the cost vs benefit curve goes parabolic. which is the point of the ludicrous statement about using $5/liter water. for most folks, its not realistic.

to my original and still-forgotten question- a simple test by someone with a cold co2 tank and an o2 sensor will tell us how effective a cold slow purge is. and at that point, with actual data to review instead of stupid claims and counterclaims about the laws of physics, folks will be able to make up their own minds about whether they'd rather cold slow purge, 5x purge, or do the starsan purge.

let's do the test, then give people the data, and let them make up their own minds.
why dont you agree?
 

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I do this for all beers, but I really pinned this down as the nail in the coffin for hitting IPAs out if the park. My IPAs were always good, great in my opinion. Still, the taste after force carbing was never as out of this world as the final gravity samples tasted. I'm confident it's because if there's any small fraction of O2 present when force carbing, that's essentially force oxygenated immediately. Now, my IPAs taste as nice after a month as they do out of the fermentor.

That's just what I do. I'm sure haters gunna hate.

Like TAK, my IPAs would never taste as good as the gravity samples did after bottle conditioning. I ended up attending a class held at a local brewery (El Segundo Brewing - winners of a gold medal in 2015 for their Hammerland IPA at the IPAfest in Hayward CA) on oxidation. They stated that they try to limit O2 in their bottling line down to the parts per billion. Actually, I think it's to parts per million but let's just say it's REALLY low.

They brought out 3 bottles of beer - 1 week old, 1 month old, and 2 months old. There were big differences between all of them. As the beer got older the hop profile got flat and muddled. I didn't taste that "cardboard" taste that everybody describes oxidation as.

After that, I started kegging into sanitizer filled then CO2 purged kegs - filled using a CO2 push from a conical into the keg's liquid out post. And my IPAs are immensely better because of that. Do you need to do this for all styles? I don't think so. But I really do think that IPAs that are loaded with and feature hops will benefit from this simple step. Do I keep my O2 levels down in the ppm levels? Probably not but they are low. When I dry in the keg, I simply purge the headspace several times. It takes seconds.

So OP, give it a try and see what you think. And quit bringing up such controversial topics as keg purging!

Cheers all!
 

leesmith

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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 :mug:
Is this chart strictly for a 5 gallon keg and since I use 2.5 gallon kegs would I have to purge half as many times?
 

doug293cz

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Is this chart strictly for a 5 gallon keg and since I use 2.5 gallon kegs would I have to purge half as many times?
These charts are independent of keg volume and headspace volume. They tell you the concentration of O2 after purging. To know the total O2 (total weight), you need to multiply the concentration by the headspace volume, and the density of O2 in weight/volume.

Brew on :mug:
 
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