Stratification of gases in closed environments (Like fermentors and kegs)

[Setesh]

A more effective means is to fill the keg completely full with water (which has been boiled to kill anything in it) and then push that out with CO2.

Clearly you would want to 'daisy chain' several kegs if you do this. Too much trouble for just 1 keg.

I think this sounds like a workable idea, but you would need a lot of fittings to make 'bridges' out of.
Boil 6 gallons of water, fill up corny keg 1 to the rim, put on lid, attach CO2 line, attach beer out line on keg 1 to gas in line on keg2, and daisy chain them all the way down the line. You leave the purge valve open on the last keg and pump the water through all of them to the end. Because of the dead space at the bottom of each keg you would end up with water loss of a couple of ounces on each keg though. I don't see a way around that unless you did it one keg at a time. You then fill them via the beer in line and you have no O2 exposure.

 

[ajdelange]

You want every mL of air pushed out so you would want to fill completely through the liquid line with the gas connector off then open the pressure release valve and push more liquid until it is coming out the pressure release. Then connect the next keg in series and continue for that one and so on. Yes, you would have to make up some 'jumper' lines.

Leave some CO2 pressure on each keg (you will want to do that anyway for counter pressure filling), disconnect the lines. Depress the poppets briefly so any liquid left in the filler or gas tubes gets blow out. Now invert the kegs so that the remianing liquid in them runs down onto the lid and then open the PRV lever briefly. This will blow the last of that liquid out. I wouldn'r want a couple of hundred mL of even no rinse sanitizer left in the keg to mix with my beer.

It's been so long since I used Cornies that I can't remember how I used to do it. If you purge with CO2 3 times to get air down to 1/27 of a kegfull (that's 700 mL of air with 140 mL of O2 in it) and then fill with beer until it comes out the gas line and PRV you will have pushed out all the air and while you have exposed the beer to that 140 mL of oxygen during the filling process that is 27 times better than the exposure it would have had if you filled the keg w/o having purged first.

 

[Yooper]

It's been so long since I used Cornies that I can't remember how I used to do it. If you purge with CO2 3 times to get air down to 1/27 of a kegfull (that's 700 mL of air with 140 mL of O2 in it) and then fill with beer until it comes out the gas line and PRV you will have pushed out all the air and while you have exposed the beer to that 140 mL of oxygen during the filling process that is 27 times better than the exposure it would have had if you filled the keg w/o having purged first.

And for me, that's been good enough for all of my kegs.

I purge, keg, purge, and set it in the kegerator. Normally, the beer is gone in a couple of weeks, but not ever more than a month. Since oxidation flavors worsen with time, this really hasn't been an issue with me at all.

Of course, I drink my beer pretty quickly. If I'm not drinking it quickly, then I will bottle (via my beergun) it but that's only happened a couple of times in the last few years.

 

[AnOldUR]

I think this sounds like a workable idea. . .

Workable, sure. Sane, not even close. Say you have less than two inches of head space in your keg and 1.2% of that is ambient air after purging. Only 21% of the 1.2% is even oxygen. As the keg is served the percentage becomes even less. And given the original volume in the head space this all seem a bit OCD even for me. :cross:

 

[ajdelange]

Quite sane, actually. Some of the best brewers I know use such techniques and are able to enjoy their beers for a year or more. These are guys that brew lots and lots of beer and want to make comparisons over a period of time as they research modifications to their processes for a particular style for example (I'm thinking of Gordon Strong here). If you brew a batch and knock it back within a few weeks then it's not necessary to do any of this. You can just siphon from the carboy into an open Corny and put the lid on but if you are a serious brewer your beer is never touched by air from the time you seal the fermenter at pitching until the time it hits your glass. You clearly do not understand how sensitive beer is to O2.

 

[AnOldUR]

. . . but if you are a serious brewer your beer is never touched by air from the time you seal the fermenter at pitching until the time it hits your glass. You clearly do not understand how sensitive beer is to O2.

 

[Dolomieu]

You guys need to stop adding so much O2 to your kegs. I store mine with air, which is mostly N2. Its only about 20% O2. Also the solubility of co2 is much greater than O2. You could spend a little time with hernys law and figure out the precise amount of o2 would enter your beer at what pressure. I would do it for you but I stopped doing other peoples homework a long time ago.

 

[ajdelange]

It has little to do with Henry's law. It is well known in the industry that even minute amounts of oxygen in the headspace of a beer package will result in the staling of beer that is to be kept for even relatively short periods of time. One of the reasons the bottling machine is the most expensive piece of equipment in the brewery is because of the great difficulty in keeping 'airs' down. Savvy home brewers learn from what the commercial guys already know. They regard oxygen with about the same level of esteem they grant pediococcus.

 

[Setesh]

Quite sane, actually. Some of the best brewers I know use such techniques and are able to enjoy their beers for a year or more. These are guys that brew lots and lots of beer and want to make comparisons over a period of time as they research modifications to their processes for a particular style for example (I'm thinking of Gordon Strong here). If you brew a batch and knock it back within a few weeks then it's not necessary to do any of this. You can just siphon from the carboy into an open Corny and put the lid on but if you are a serious brewer your beer is never touched by air from the time you seal the fermenter at pitching until the time it hits your glass. You clearly do not understand how sensitive beer is to O2.

That's what I was thinking it would be useful for. Something that is going to be around a very long time. A Hefe I wouldn't bother, but a Barleywine I think could benefit. Is it anal? maybe. Does that bother me? Not in the least!

 

[Setesh]

Not to take away from the fighting, but does O2 have to dissolve to cause damage? Can't it oxidize the surface layer of the beer without dissolving into solution? That's how oxidization occurs on solids like metals, right?

 

[Dolomieu]

Do you have a lot of iron in you wort? If not how is it the same?

 

[Dolomieu]

Is O2 the only oxidizer you are concerned with? If so why?

 

[ajdelange]

...does O2 have to dissolve to cause damage?

Yes, to get to the reductones in the beer, but it does readily. Oxygen moves into the beer along a gradient of chemical potential i.e. if you put beer which has been protected from O2 i.e. beer in the reduced state under gas which contains O2 the O2 will move into the water as long as that gradient exists. Reduced beer contains reductones. These will absorb that O2, becoming oxidized in the process and removing it from the solution so that the gradient is maintained and O2 continues to flow in until no O2 remains in the headspace and the gradient evanesces. This is why Henry coefficient has nothing to do with it. The Henry coefficient tells us how many mg/L DO are required to equalize the chemical potential of dissolved oxygen in water in equilibrium with the gas over it. Here saturation is never approached as the partial pressure of O2 in the beer is effectively 0 as the O2 is taken out of solution by the reductones.

Can't it oxidize the surface layer of the beer without dissolving into solution? That's how oxidization occurs on solids like metals, right?

Clearly the reductones at the surface will be the first to be oxidized as is the case with a metal but there is a difference. In the metal the oxide forms a protective layer which O2 cannot penetrate. In the beer the oxidation products do not form a protective layer as they are dissolved at low concentration in the beer. O2 can flow right past them into the other parts of the wort (as there is the potential gradient to them too). All this takes time, of course. It can take months at cold temperatures for a beer to stale

Is O2 the only oxidizer you are concerned with? If so why?

More or less. A good brewer will do everything he can to keep his wort/beer in the reduced state which means avoiding even brief exposure to oxygen on the hot side where damage can be quick and ensuring that the beer, once past the oxygenation which follows pitching (exception for ales that are 'dropped'), is protected from oxygen especially after the yeast are removed i.e. in the package.

I guess we could say brewers who use ascorbic acid for chloramine reduction/removal are concerned with another oxidizer i.e. dehydroascorbic acid, and those who use ascorbic acid for chloramine, or as an oxygen scavenger, also use some metabite to keep things in the reduced state. But in general the threat is O2. Yeast like things reduced and are excellent at keeping the ORP low. It is when the yeast go dormant or are removed that we have to worry about oxidation by O2 because the yeast can no longer compensate for it. Plus I can do something about O2 as described in earlier posts. If I had Fe+++ ions in my beer there wouldn't be much I could do about it (except be sure before water hits malt that there isn't any Fe+++ in the water).

Some brewers, as noted above, add bisulfite or ascorbate and bisulfite to their beer to keep them reduced (Gordon is one of those). I suppose you could say they are concerned about other oxidizers as these are effective against more than O2 but they do, of course, provide protection against O2 as well.

 

[Dolomieu]

C02 is more soluble than O2. Purging your vessel greatly dilutesthe already diluted O2 present in it. This is again some one vastly over stating the issue. Yes its a concern, but really how far are you capable of going?

If you want a demo on how gasses mix/settle, get some dry ice and toss it in a bucket. If you think there is any O2 left try breathing with your head in there. (Please don't)

Classic mountain made of a mole hill

 

[Dolomieu]

You can also say those who don't treat for cl are at risk as cl can also act as an oxidizer. This is all great theory. Lots of things could happen but in practice your posts read as verbal masturbation. Some poor brewer is going to read your posts with its condensending "any good brewer" bs and get discouraged.

 

[Beernik]

I agree. I'm not a keg wiz, but this seems to have turned from practical to theoretical. It sounds like tying up two kegs to protect a third. If you're that paranoid about oxygen, bottle with O2 absorbing caps.

 

[ajdelange]

Well let's try to take this back to the practical. A commercial brewer will shoot for perhaps 200 ppb TPO. It's easy enough to figure out what that means in terms of a 19L (19,000 cc) Corny keg: 200E-9* 1.9E4 = 3.8 mg O2. As oxygen weighs about 1.4 mg/cc you could, at STP, tolerate 2.7 cc of pure O2 in a 19L Corny at 200 ppb. Air is about 1/5 O2 so that means you could have 13.6 cc of air. If you do the triple purge you can have 27 times that or 366 cc of air which is probably about the size of the headspace in a normal fill and will give you about the shelf life of typical commercial beer. If you want longer (I do and enjoy many of my beers for over a year) then you must either reduce the oxygen content in the headspace or reduce the headspace. You can lower the TPO by a factor of 3 for each CO2 purge cycle (wasting a kegfull of CO2) or you can lower it by a factor of three by reducing the headspace to 1/3. This can be done by bleeding from the PRV instead of the gas port as you fill but you will then have doubtless filled above the lower end of the gas dip tube and will have to be careful when the keg is tapped. Or you can fill till beer comes out of the PRV port and have removed all oxygen (except that which dissolved when filling and if you have purged a couple of times with CO2 that should be minimal). Or you can use the water (or steam) displacement trick to insure 0 headspace O2. This has the advantage that you will be filling against CO2 counter pressure which causes any O2 dissolved in the beer to move from the beer to the headspace (chemical potential gradient again) during filling. This gets TPO even lower than a commercial brewer would typically attain as (AFAIK) they don't fill against counter pressure (except the very small ones that use manual bottle fillers). Going below what the pro's shoot for is arguably getting a bit AR but one of the main reasons I brew is to have beer better than I can buy.

That's how it is, like it or not. You can call it making a mountain out of a mole hill or you can learn something from it and potentially improve your beer. For more information Google 'TPO beer'. I was surprised to find in doing this that Hach has acquired Orbisphere - a company that owes its existence to existence of this mountain - which explains why Hach is a sponsor of this years MBAA conference.

 

[ajdelange]

This is all great theory. Lots of things could happen but in practice your posts read as verbal masturbation.

This is the Brew Science page where we have
"In depth technical threads related to the biology and chemistry of home brewing"

Presumably you are here either to learn or contribute. If you know what Henry coefficient is (you mentioned it) you should be able to follow the rest of the p-chem. If you were acquainted with modern brewing science and practice you would be aware of the practical application of what we are discussing here. This isn't a textbook so not every statement is in logical order nor presented in the optimum way but reading back over this most of the discussion has been sound. Even the skeptics, who should be skeptical - it's how much of learning takes place, have been respectfully skeptical - except for you. If you have some solid basis for your skepticism put it forth. Support your argument with calculations, numbers, references to the literature etc.

 

[ajdelange]

If you want a demo on how gasses mix/settle, get some dry ice and toss it in a bucket. If you think there is any O2 left try breathing with your head in there. (Please don't)

There is lots of O2 left but the amount of CO2 is enough to cause you great distress (yes, I have done this or, to be more precise, stuck my head into a fermenter).

 

[Yooper]

This is the Brew Science page where we have
"In depth technical threads related to the biology and chemistry of home brewing"

Exactly. This is not "Beginner's Brewing" or even "General Techniques"- this is the Brew Science forum.

I will ask that personal attacks and comments not be in any of the posts. Thanks!

 

[Setesh]

If you want a demo on how gasses mix/settle, get some dry ice and toss it in a bucket. If you think there is any O2 left try breathing with your head in there. (Please don't)

Classic mountain made of a mole hill

I don't think that analogy is sound. Dry ice fog is not only CO2, but also water, which is extremely heavy. The fog is also very cold. These characteristics make that more of an apples to oranges analogy in this discussion.

 

[Dolomieu]

I don't think that analogy is sound. Dry ice fog is not only CO2, but also water, which is extremely heavy. The fog is also very cold. These characteristics make that more of an apples to oranges analogy in this discussion.

Not true. It is solid CO2 if it picks up moisture it's from its surroundings. Just because it is called ice does not mean there is H20 in it's formulation.

 

[ajdelange]

We noted many posts back that layers do form. I think your basic questions relate to things like 'Do they persist given mixing?' If you put a lump of dry ice in a volumetric flask and wait a while certainly most of the air will eventually be displaced even if there is a lot of mixing. There would be precious little air in the bottom of that flask.

But if you put a lump of dry ice in a beaker the story would be different, at least near the interface where normal convection and the thermal velocities of the particles are enough to produce mixing.

However, if one were to make a mix of 20% O2 and 80% CO2 i.e. just swap the nitrogen in air for CO2 and try to breathe that he would be in for a plenty unpleasant experience. The CO2 reacts with the moisture in the lungs in to form carbonic acid and, as I know from personal experience, that's painful.

 

[ajdelange]

I will ask that personal attacks and comments not be in any of the posts. Thanks!

You're quite right. I was going to delete the post but I guess I'll leave it with the offensive part removed. Sorry about that. I'm usually pretty patient but I have my limits.

 

[Dolomieu]

I understand that and have been following you. Now make that 20% Air (which only 20% of that is O2) 80% CO2. This is where I believe the meat is. Talking as if there is 20% pure O2 in the keg is misleading.

 

[Yooper]

I understand that and have been following you. Now make that 20% Air (which only 20% of that is O2) 80% CO2. This is where I believe the meat is. Talking as if there is 20% pure O2 in the keg is misleading.

Correct- room air (we call it RA in medical talk) is not 100% o2 of course- the major gas is nitrogen. That was mentioned here:

...........{snip}.......If you purge with CO2 3 times to get air down to 1/27 of a kegfull (that's 700 mL of air with 140 mL of O2 in it) and then fill with beer until it comes out the gas line and PRV you will have pushed out all the air and while you have exposed the beer to that 140 mL of oxygen during the filling process that is 27 times better than the exposure it would have had if you filled the keg w/o having purged first.

And of course, my response was that it's "good enough" for me- but it helps to know why we purge and what we accomplish.

And for me, that's been good enough for all of my kegs.

I purge, keg, purge, and set it in the kegerator. Normally, the beer is gone in a couple of weeks, but not ever more than a month. Since oxidation flavors worsen with time, this really hasn't been an issue with me at all.

Of course, I drink my beer pretty quickly. If I'm not drinking it quickly, then I will bottle (via my beergun) it but that's only happened a couple of times in the last few years.

The reason we're having this discussion is because one of the things that we hear over and over in the forum is "Don't worry about oxidation! The c02 blanket will protect your beer forever and ever!". (Of course, I'm paraphrasing).

Winemakers take oxidation very seriously, and top up the wine as well as use antioxidants (sulfites) in the wine to protect it. Since we don't tend to use sulfites in our beer, it's helpful to realize the mechanism of oxidation and how it occurs.

I'm sure we've all had some long bottled barleywines that display signs of oxidation, but I think most beers I've ever had also display signs of oxidation, however slight.

Most of the beers I've tasted in competitions display some oxidation signs. Are they severe? No, not usually. But often present. That's why I cringe when I read on the forum, "I poured my beer into the bottling bucket, and then poured it into the bottles, and I have NO oxidation at all!" The truth is that maybe they don't have the "cardboard" flavors that are always talked about when discussing oxidation- but I bet there are sherry notes, a staling/subduing of the malt, and possible some astringent hop notes.

Each brewer can decide what's "good enough" for them. For some, perfection is the goal. For me, beer that I enjoy and enjoy sharing with others is my goal. I take reasonable steps to prevent signs of oxidation detracting from the beer before it's gone- and that's about it.

I think the discussion of the stratification of gases (i.e. the "co2 blanket") merits discussion from a scientific standpoint.

 

[Wynne-R]

I get that the ‘CO2 blanket’ is wishful thinking propagated by people that know nothing of gas law. However, they’re not completely wrong. Check me out on this.

A batch in primary is going to float out most of the oxygen and it will be slow to come back through the airlock. This will work better in a carboy than in a bucket.

When I go to secondary, I usually have a liter or so of headspace. I routinely add 50g of sucrose with the idea that the resultant CO2 will displace most of the air.

Now it seems there is a lot more air in there than I’d imagined. I’d probably be better off filling the secondary to the neck.

Any thoughts?

 

[dyqik]

I don't think that analogy is sound. Dry ice fog is not only CO2, but also water, which is extremely heavy. The fog is also very cold. These characteristics make that more of an apples to oranges analogy in this discussion.

The temperature really does matter - liquid nitrogen will boil off in an open container, leaving an almost completely oxygen depleted cold nitrogen gas volume in the container (a small rubbermaid cooler in this case - about 16 quarts), _under_ the slightly higher molecular weight, but warmer, air. In a still room, it will take hours to mix, introducing oxygen into the nitrogen blanket, and ultimately the liquid nitrogen. My colleague is preparing a paper on what happens to this oxygen, and what it does to the boiling point of the liquid nitrogen at the moment, as this has implications for the calibration of radio and millimeter wave astronomical instruments.

Cold CO2 gas from a dry ice machine is deliberately mixed with damp air, and the visible fog is water vapor condensing to droplets suspended in the cold dense air/CO2 mixture. CO2 itself is invisible (except as a "mirage" type change in refractive index in the air if it settles in still environment).

 

[dyqik]

Oh, and English real ale needs a small amount of oxidation to get the best flavor from the it. Controlled amounts of oxidation can be a good thing as long as all the oxygen present is then bound up, and the beer doesn't oxidize further.

 

[Yooper]

Oh, and English real ale needs a small amount of oxidation to get the best flavor from the it. Controlled amounts of oxidation can be a good thing as long as all the oxygen present is then bound up, and the beer doesn't oxidize further.

The key to a great cask isn't the "bound up" oxygen, but instead that the cask is emptied before the beer deteriorates to an objectionable flavor.

You can taste it- the first pint is much different than the last pint as the beer oxidizes.

Slight oxidation flavors can be very pleasant- a "sherry" or sweet-ish "brandy" flavor is most common and very nice in barleywines and in some other dark beers. They aren't great in pale ales, though, and of course they worsen with time. A slight flavor of oxidation today could be cardboard flavor in 2 months.