No. The headspace is just as wide.
purging kegs
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No. The headspace is just as wide.
hotwatermusic
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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.
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.
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hotwatermusic
Well-Known Member
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.
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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.
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hotwatermusic
Well-Known Member
Cool, got it now, thanks.
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
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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.
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Thanks for the clarification, I assumed that was the case but had to ask.
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.
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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?
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
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You will not regret kegging......period.
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.
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.
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 its worth it is a choice for you to make.
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 its worth it is a choice for you to make.
Argie86
Active Member
Good info in here, just a question. How long can you store a corny full with star at room temp??
I wouldn't keep it in there more than 5 years.
Agreed.
That'd be roughly 4.9 years too long
That'd be roughly 4.9 years too long
Not trying to start/continue an argument, but I have been thinking about this alot:
After reading about this and other similar threads, I understand that if you do the Star San fill and then push with C02, you will use less C02 then if you have a gallon's worth of head space. I also understand that doing it this way guarantees no O2 in the keg after the purge of the Star San. That is all good, as I think the consensus seems to be that O2 is bad in the long term.
However, I have a few observations/comments/questions:
1. Pushing Star San will still leave a few oz of star san in the keg. I know that I have suds left over in my kegs after sanitizing, but the amount of Star San after sanitizing and letting drain upside down will not be as much as is left when pushing Star San out with CO2. Probably not a big deal compared to 5 gallons, but it seem that we might be picking hairs here concerning O2, so why not pick hairs with a few oz of Star San leftover in your beer.
2. I almost never have a gallon's worth of head space in my keg. Maybe more like an 1/8 to a 1/4 gallon. So, then the purge the headspace technique might use less than pushing 5 gallons of Star San.
3. Now comes the question part. It has been over 20 years since my last Heat and Mass Xfer class, so I don't remember off the top of my head the equations for diffusion of gas into a liquid, but I do remember that it is a slow-ish process. As has been mentioned, it is sped up by turbulence, increased surface area, pressure, temperature, etc. My usual process is simply to sanitize my keg, then rack from the fermenter into the bottom of the keg (without purging the keg ahead of time). I keep the racking tube submerged under the beer to prevent splashing (you definitely get splashing at the very beginning, but that subsides quickly). After that, the only way for oxygen to get into the beer is through diffusion of the upper beer surface in the time it takes to fill the keg. The surface of the beer is rising, so there is some motion and diffusion is faster than if it was completely stationary, but I am guessing that not much diffusion occurs. The beer surface area is pretty small and the motion is also small, and the time exposed to oxygen is a matter of minutes. I fill the keg up to near the top, and then purge the head space using several repeated charges of CO2. Has anybody done any calculations to try and estimate how much oxygen is absorbed in that small amount of time through the small beer surface area as the keg has been filled? I just don't see how much could diffuse under the circumstances. Maybe I should break out the old Mass Xfer book and see if I can calculate it....
The video shown earlier in the thread showed that it is fairly quick for two gases diffusing, but this is different - we have a gas and a liquid.
After reading about this and other similar threads, I understand that if you do the Star San fill and then push with C02, you will use less C02 then if you have a gallon's worth of head space. I also understand that doing it this way guarantees no O2 in the keg after the purge of the Star San. That is all good, as I think the consensus seems to be that O2 is bad in the long term.
However, I have a few observations/comments/questions:
1. Pushing Star San will still leave a few oz of star san in the keg. I know that I have suds left over in my kegs after sanitizing, but the amount of Star San after sanitizing and letting drain upside down will not be as much as is left when pushing Star San out with CO2. Probably not a big deal compared to 5 gallons, but it seem that we might be picking hairs here concerning O2, so why not pick hairs with a few oz of Star San leftover in your beer.
2. I almost never have a gallon's worth of head space in my keg. Maybe more like an 1/8 to a 1/4 gallon. So, then the purge the headspace technique might use less than pushing 5 gallons of Star San.
3. Now comes the question part. It has been over 20 years since my last Heat and Mass Xfer class, so I don't remember off the top of my head the equations for diffusion of gas into a liquid, but I do remember that it is a slow-ish process. As has been mentioned, it is sped up by turbulence, increased surface area, pressure, temperature, etc. My usual process is simply to sanitize my keg, then rack from the fermenter into the bottom of the keg (without purging the keg ahead of time). I keep the racking tube submerged under the beer to prevent splashing (you definitely get splashing at the very beginning, but that subsides quickly). After that, the only way for oxygen to get into the beer is through diffusion of the upper beer surface in the time it takes to fill the keg. The surface of the beer is rising, so there is some motion and diffusion is faster than if it was completely stationary, but I am guessing that not much diffusion occurs. The beer surface area is pretty small and the motion is also small, and the time exposed to oxygen is a matter of minutes. I fill the keg up to near the top, and then purge the head space using several repeated charges of CO2. Has anybody done any calculations to try and estimate how much oxygen is absorbed in that small amount of time through the small beer surface area as the keg has been filled? I just don't see how much could diffuse under the circumstances. Maybe I should break out the old Mass Xfer book and see if I can calculate it....
The video shown earlier in the thread showed that it is fairly quick for two gases diffusing, but this is different - we have a gas and a liquid.
If the dip tube is appropriately positioned in the bottom of the keg there won't be but a few drops left. Whether this is star san, or water, there will be oxygen in that water.
If you wanted to deal with most of this remaining oxygen you could
1. Use boiled water
2. Add some sulfites to the water to try to reduce the amount of oxygen.
3. Spund the keg and allow the yeast to scavenge any remaining oxygen
... or some combination of 1 or more of the above, which #3 trumping all the others.
If i remember correctly it takes like 30 purges at 30 psi to dilute the air inside the keg down to what is considered ok levels. This also assumes perfect mixing. You can push an entire keg of water with just a couple psi.
The diffusion of oxygen from air into water (or beer) is actually quite fast. The calculations and numbers have been discussed around here before. Maybe someone can dig up a thread link.
13 purge cycles at 30 psi to get to 0.11 ppm O2 in headspace. In the case of imperfect mixing, you likely have higher CO2 concentration low in the headspace and higher O2 concentration higher in the headspace. So, purging via the PRV will be even more effective per cycle than with perfect mixing.
A "full" keg has about 1/3 gal headspace, and 30 psi is about 2 atm, so each purge cycle will use about 2/3 gal of CO2. Thirteen purge cycles will use about 13 * 2/3 = 8.7 gal.
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I would like to see that. Every paper I have looked up so far indicates that it is a slow process. I haven't had any luck finding a similar discussion on this site. I'll keep looking.
TapTakeOver
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Folks there is a ton of incorrect information in this thread. Trying to correct a couple inaccuracies to help out here and save folks a lot of cash.
A couple items of note:
1) I hate to be the bearer of bad news but one should never put unsanitized tap water in a sanitized keg without resanitizing prior to adding your brew. If you think tap water is “clean” you are mistaken and it doesn’t matter where you live.
2) CO2 is quite a bit heavier than O2 (remember the C in CO2 is Carbon) so CO2 is C+O2. Given this quality it is not necessary to purge a keg multiple times to remove virtually 100% of O2.
3) Simply pushing CO2 through liquid post at low psi while opening keg safety release valve for a few seconds is sufficient to remove O2 from a keg. As CO2 is heavier than O2 it will not “leak” out if keg topper is opened (this should be done in a draft free environment).
4) Here is a simple video that clearly shows the weight differences between CO2 and O2.
Happy brewing....”relax, don’t worry, have a home brew”
A couple items of note:
1) I hate to be the bearer of bad news but one should never put unsanitized tap water in a sanitized keg without resanitizing prior to adding your brew. If you think tap water is “clean” you are mistaken and it doesn’t matter where you live.
2) CO2 is quite a bit heavier than O2 (remember the C in CO2 is Carbon) so CO2 is C+O2. Given this quality it is not necessary to purge a keg multiple times to remove virtually 100% of O2.
3) Simply pushing CO2 through liquid post at low psi while opening keg safety release valve for a few seconds is sufficient to remove O2 from a keg. As CO2 is heavier than O2 it will not “leak” out if keg topper is opened (this should be done in a draft free environment).
4) Here is a simple video that clearly shows the weight differences between CO2 and O2.
Happy brewing....”relax, don’t worry, have a home brew”
You've perhaps just made THE MOST inaccurate posts of the entire thread.
This is perhaps the most accurate statement of your entire post in that tap water isn't necessarily completely sanitary. However in nearly all cases it is clean *enough* in the same way that the sanitizer products we use get equipment clean *enough*. Also this is the fermented beer stage. The pH alone makes it undesirable for most critters.
CO2 is heavier than O2, but due to mixing the rest of your statement is complete and utter nonsense.
Complete and utter nonsense due to mixing of the gasses.
This video demonstrates the difference in density, but it doesn't demonstrate the entire environment has been purged of oxygen, just that its been purged enough to put out a candle. That's really not very hard and only requires less than half the oxygen be displaced.
If gases worked this way, we would all die of suffocation as all the O2 went to the top of our atmosphere and all the CO2 settled. Well, Denver might survive...
I believe @schematix on this stuff very much more than I believe the survival doc. However I’d really like to see some experimental data using a ppb sensitive DO meter on some of the keg purging techniques that I see on this and other forums being supported by lots of math and pretty graphs.
I’d like to see...
DO in beer in purged keg using the following techniques
No purge, just gravity fill with minimal splashing then purge the headspace with CO2 half a dozen times
Purge keg a few times then fill closed transfer
Purge keg with a full star San push then fill closed transfer
Purge keg with boiled water push then fill closed transfer
All of the above followed by
Force carbing
Opening top and priming sugar followed by purging head space
Spunding
Then finally don’t forget keg after one week hooked up to CO2 in kegerator
It’s not like I don’t believe math but you know what the say about figures never lie but liars do figure.
So where is the DO measurement to support all this purging math?
I’d like to see...
DO in beer in purged keg using the following techniques
No purge, just gravity fill with minimal splashing then purge the headspace with CO2 half a dozen times
Purge keg a few times then fill closed transfer
Purge keg with a full star San push then fill closed transfer
Purge keg with boiled water push then fill closed transfer
All of the above followed by
Force carbing
Opening top and priming sugar followed by purging head space
Spunding
Then finally don’t forget keg after one week hooked up to CO2 in kegerator
It’s not like I don’t believe math but you know what the say about figures never lie but liars do figure.
So where is the DO measurement to support all this purging math?
I actually authorized this post out of the moderation hold queue, but it was time to leave for dinner, so I was hoping someone else would step up to the plate with corrections. @schematix covered the errors pretty well. It anyone wants more gory detail and references, let me know.Noobs are fun, especially with fundamental stuff.
@doug293cz should be along any minute to fix all the broken china
Brew on
a
So you could have prevented a train wreck but you thought it would be entertaining?
Cheers!
Cheers!
There's a lot of info out there already so i'm not going to rehash it all. This link has been posted here before and is one of the most thorough explanations i've seen: http://www.********************/brewing-methods/beer-serving-oxygen-ingress/
The gist of it is that oxygen comes from multiple sources, including packaging and even after that since there's no such thing as a perfect seal. It is also consumed (i.e. reacts with other compounds) inside the keg so that it's not just free dissolved oxygen anymore. You can't measure that.
The dilution math has been established p-chem for more than a century. The limitations to the analysis are:
- It assumes complete mixing of the existing head space gas with the purge gas. In cases of imperfect mixing, the higher density of the CO2 will mean the dilution is even greater than the assumed case, so the calculated numbers are pessimistic (i.e. residual O2 will be lower than calculated.)
- It assumes pure CO2. The spec for beverage grade CO2 is 30 ppm O2 max, so suppliers only test well enough to insure the O2 is less than 30 ppm. They don't actually measure actual O2 ppm. I have seen some data that says bev grade CO2 typically actually runs about 50 ppb (0.05 ppm.) I've been trying to (re-)find the link for the reference, but haven't had success. Obviously, the final O2 concentration for infinite purges limits out at the O2 concentration of the CO2.
- It assumes that no air (O2) leaks into the system due to process or equipment deficiencies.
Naturally, if you have the capability to do actual measurements, with properly operated and calibrated equipment, your results will be better than calculated estimates. However, good DO meters/probes are expensive, and most homebrewers cannot afford, or justify the cost. If you don't have a DO meter, the only things you can do are optimize your process and equipment, and use the calculated estimates to get to what you think is close enough.
Brew on
Not really. As moderators, we only check to see that the held posts comply with HBT rules, and approve anything that does. We don't pass judgement on technical validity. And, I don't think you would want us to do so. So, my only choice was to approve the post, and come back later and address the technical inaccuracies in a reply post. That gives the OP, and other members, a chance to weigh in on both the OP and any replies.So you could have prevented a train wreck but you thought it would be entertaining?
Cheers!
doug293cz
Of course, I totally get all that.
I should have stuck the "Rhetorical Question" tag on that. My bad...
Cheers!
I should have stuck the "Rhetorical Question" tag on that. My bad...
Cheers!
I knew it was probably a rhetorical question, but thought that providing a little insight into how moderation is done might be helpful to people (especially those that didn't realize it was a rhetorical question.)Of course, I totally get all that.
I should have stuck the "Rhetorical Question" tag on that. My bad...
Cheers!
doug293cz
I’ve read all or most of that. I like the idea but I’m not a fan of “you can’t measure that”. Clearly pros do measure DO at multiple points in their process, especially in packaging. I’m interested in seeing a pro level packaging measurement applied to typical vs advance vs extreme home brew packaging processes. I’m interested in an instrument measurable variable since sensory analysis seems to give results all over the map.
And haha no I’m not willing to buy an expensive instrument but am optimistic someone with access to such an instrument will try this. The only thing I’ve seen so far that was close to what I’m talking about was on brulosophy’s test of the beer gun. I’d like to see more tests like that.
I'd be shocked - SHOCKED - if the LoDO folks haven't done a comprehensive multiphase analysis of O2 uptake - starting before you've even bought the grain...
http://www.********************/
Cheers!
http://www.********************/
Cheers!
