purging kegs

[doug293cz]

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

 

[dunbruha]

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

 

[Rev2010]

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.

 

[TAK]

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.

 

[slugsly]

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.

 

[dunbruha]

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]

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?

 

[PlinyTheMiddleAged]

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]

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

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]

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

 

[Yooper]

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?

No. The headspace is just as wide.

 

[hotwatermusic]

For those who are filling thru the liquid out posts after liquid purging their kegs, how do you deal with existent O2 in the lines when transferring beer from the FV? That would still seem to be part of the "closed system".

 

[schematix]

For those who are filling thru the liquid out posts after liquid purging their kegs, how do you deal with existent O2 in the lines when transferring beer from the FV? That would still seem to be part of the "closed system".

Purge them with CO2 before racking.

 

[doug293cz]

For those who are filling thru the liquid out posts after liquid purging their kegs, how do you deal with existent O2 in the lines when transferring beer from the FV? That would still seem to be part of the "closed system".

I use the same tubing I used to drain the StarSan for racking. No disconnection between processes. The tubing is full of CO2 after all the SS is blown out.

Brew on

 

[hotwatermusic]

I use the same tubing I used to drain the StarSan for racking. No disconnection between processes. The tubing is full of CO2 after all the SS is blown out.

Brew on

So are you using a quick disconnect to evacuate the starsan, and connecting that same disconnect attached to your fermenter?

 

[doug293cz]

So are you using a quick disconnect to evacuate the starsan, and connecting that same disconnect attached to your fermenter?

Liquid QD on the keg side, open end on the other. When draining StarSan, open end goes in the catch bucket. Lots of CO2 gets blown thru when the keg empties. Leave the tube attached to the keg, put thumb over open tube end while still submerged in the StarSan, then attach open end to spigot on the fermenter. If using a racking cane, attach tube end to cane, blow a little CO2 thru, then place cane in fermenter. I pressure transfer from the fermenter in this case, so don't have to get a siphon started.

I stilll do some purge cycles after the keg is full, just to take care of whatever O2 managed to sneak in.

Brew on

 

[hotwatermusic]

Cool, got it now, thanks.

 

[ba-brewer]

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

What is your definition of a purge cycle for your charts, a complete depressurization and pressurize or a blast/burp release from the PRV?

 

[doug293cz]

What is your definition of a purge cycle for your charts, a complete depressurization and pressurize or a blast/burp release from the PRV?

Pressurize to the specified pressure, then pull the PRV until gas flow stops (no more hissing.) The math is based on the ideal gas law (PV = nRT) and simple dilution. It assumes you go from atmospheric pressure (0 psi gauge), to the purge pressure, and back to atmospheric pressure for each cycle.

For example: Initially you have 14.7 psi absolute pressure of air in the headspace, which is 21% O2. If you then pressurize to 14.7 psi gauge, you have twice as much gas in the headspace, and it is half air and half CO2. The headspace now is 10.5% O2. When you vent back to atmospheric pressure you are still 1/2 air and 1/2 CO2, O2 is 10.5% of total headspace. Pressurize again to 14.7 psig, and the headspace is now 1/4 air and 3/4 CO2, and the O2 percentage is down to 5.25%. Rinse and repeat.

Brew on

 

[ba-brewer]

Thanks for the clarification, I assumed that was the case but had to ask.

 

[schematix]

Pressurize again to 14.7 psig, and the headspace is now 1/4 air and 3/4 CO2, and the O2 percentage is down to 5.25%. Rinse and repeat.

Brew on

This is a really good example of why CO2 purging is not a sufficiently effective process for O2 reduction . No question it reduces it, but even after a dozen purge cycles it's still above the thresholds. Air just has a huge concentration of oxygen...

Water purging an empty keg is the only way to go.

 

[IslandLizard]

This is a really good example of why CO2 purging is not a sufficiently effective process for O2 reduction . No question it reduces it, but even after a dozen purge cycles it's still above the thresholds. Air just has a huge concentration of oxygen...

Water purging an empty keg is the only way to go.

Spot on!
Even when a 5 gallon keg is filled with only 4 gallons of beer, and the leftover 1 gallon of headspace is purged 5x (not a low oxygen standard by any means), one would be saving more CO2 with a full Starsan (or water) purge of the keg before filing it, while attaining a near O2 free keg, if done right.

I prefer to do a Starsan purge. Do you water purge to reduce the carryover of the 1-2 ounces of Starsan left in the bottom?

 

[Onthebrew]

My first ever starter keg kit arrived yesterday. No instructions came with it at all so started some research.

Now after reading this I think I may stick to bottles no for now. Is it really this complicated?

 

[PADave]

My first ever starter keg kit arrived yesterday. No instructions came with it at all so started some research.

Now after reading this I think I may stick to bottles no for now. Is it really this complicated?

I thought the same thing before starting to keg. Now I prefer it to bottling. It's only as complicated as you make it.

 

[Roland_deschain]

You will not regret kegging......period.

 

[schematix]

Kegging is actually really quite simple when you get down to it. There's a lot of good info out there. As with anything else new you'll learn about it and after the first keg kicks you'll wonder why you didn't do it sooner.

 

[Onthebrew]

It just seemed to me people are getting fixated with wiping out all oxygen, so that was putting me off. When you bottle you leave an inch at the top so what's the issue? Just do a bit of purging and should be ok right?

 

[Sadu]

It just seemed to me people are getting fixated with wiping out all oxygen, so that was putting me off. When you bottle you leave an inch at the top so what's the issue? Just do a bit of purging and should be ok right?

The key difference is that you add priming sugar to the bottle as well, so you have active yeast to help eat up the O2 in the bottle headspace. This is not the case with kegs unless you naturally condition in the keg.

I think the key thing is to figure out what works for you. The standard purge-release cycle method works ok and is easy - but uses more gas and is inferior at removing O2 compared with a liquid purge. If you are new to kegging I'd say just do what is easiest initially. And if you are happy with that and like how your beers taste, great. Lots of brewers do well with this method.

Personally I have noticed a marked difference in beer quality since I started really paying attention to oxygen exposure. Ferment under pressure, closed transfer to a properly purged keg. Figure out what works for you, feel free to try both methods and compare.

 

[schematix]

Do what works for you, but know that oxygen is a tricky beast to handle.

You can make beer without doing a single thing related to reducing oxygen exposure. If you follow strict adherence to eliminating oxygen at every step of the process you will get different flavors though. Whether it’s worth it is a choice for you to make.

 

[Argie86]

Good info in here, just a question. How long can you store a corny full with star at room temp??