Do you have a lot of iron in you wort? If not how is it the same?
Stratification of gases in closed environments (Like fermentors and kegs)
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Is O2 the only oxidizer you are concerned with? If so why?
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.
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
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.Dolomieu said:
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.
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
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
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
Well-Known Member
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.
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.
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.
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.
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).
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!
OP
OP
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.
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.
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.
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.
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:
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.
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.
I get that the CO2 blanket is wishful thinking propagated by people that know nothing of gas law. However, theyre 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 Id imagined. Id probably be better off filling the secondary to the neck.
Any thoughts?
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 Id imagined. Id probably be better off filling the secondary to the neck.
Any thoughts?
dyqik
Well-Known Member
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
Well-Known Member
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.
Maybe there is a chemistry graduate student that could take on experiments that measure O2 adsorption of wort/beer over time in a brewing environment. It does seem that everyone is in more or less agreement that the CO2 blanket concept is a misnomer and at worse, a misunderstanding of gas and laws of physics. It is a very interesting discussion however.
I have a few practical application or technique questions then, since this seems counter to many homebrewer's observations:
1. Yeast take up O2 (dissolved in the wort, not from the air) at least in the lag phase and past primary fermentation this is often believed to help prevent oxidation (I wish I could remember where I heard or read this). This appears to be untrue - as I have heard many BJCP judges state the same as Yooper. Bottle conditioned beer then should not be oxidized, unless oxidation occurred before or during bottling, correct? It seems that some people (award winning brewers) have a handle on this - and the general wisdom is the CO2 blanket idea. Everyone I have talked to supports the idea of a blast of CO2 protects the surface of beer when handling/transferring.
2. This may mean that "purging" techniques may only be effective if done specifically to introduce a high pressure differential at the bottom of a vessel (assuming the opening or valve is at atmospheric pressure) - expanding CO2 mechanically "pushing" out much of the ambient gasses like a rocket - for example - purging an empty corny using the liquid side and dip tube to put 3-5 lbs of pressure into the bottom accelerating the gas out through an open top or the pressure release valve. I am guessing this is slightly less effective than pushing a corny full of water or sanitizer out with CO2? or not? Same process for counter pressure bottle fillers that allow a burst of CO2 to purge the bottle before filling.
3. When using a secondary (very rare for me), it seems common sense to eliminate the beer surface area contact with air filling to the neck of the carboy, but not always practical. I have tried both the CO2 purge and the technique of adding a minimum sugar addition to allow new fermentation to create CO2 - and hoping that bubbling activity would provide a barrier between the beer and air. Or does the immediate application of an airlock trap the "air" causing it to mix homogeneously into the producing CO2 until the pressure begins to expel gas through the airlock?
Yes, occasionally I get oxidized beer. Sucks. Happens less and less the better care I take in handling.
I just read back through this and not sure I made a whole lot of sense. Perhaps I answered my own questions by assuming that we need to treat beer delicately through any transfer or exposure to air (or better in a sealed environment under pressure), and that most serious oxidation occurs when wort/beer is splashed or agitated (oxygenation by mechanical means), and natural aging oxidation occurs as O2 transfers through plastic, wood and or metal by passive means. It seems both can be addressed by proper processes and proper handling and storage, minimized but never completely avoided.
I have a few practical application or technique questions then, since this seems counter to many homebrewer's observations:
1. Yeast take up O2 (dissolved in the wort, not from the air) at least in the lag phase and past primary fermentation this is often believed to help prevent oxidation (I wish I could remember where I heard or read this). This appears to be untrue - as I have heard many BJCP judges state the same as Yooper. Bottle conditioned beer then should not be oxidized, unless oxidation occurred before or during bottling, correct? It seems that some people (award winning brewers) have a handle on this - and the general wisdom is the CO2 blanket idea. Everyone I have talked to supports the idea of a blast of CO2 protects the surface of beer when handling/transferring.
2. This may mean that "purging" techniques may only be effective if done specifically to introduce a high pressure differential at the bottom of a vessel (assuming the opening or valve is at atmospheric pressure) - expanding CO2 mechanically "pushing" out much of the ambient gasses like a rocket - for example - purging an empty corny using the liquid side and dip tube to put 3-5 lbs of pressure into the bottom accelerating the gas out through an open top or the pressure release valve. I am guessing this is slightly less effective than pushing a corny full of water or sanitizer out with CO2? or not? Same process for counter pressure bottle fillers that allow a burst of CO2 to purge the bottle before filling.
3. When using a secondary (very rare for me), it seems common sense to eliminate the beer surface area contact with air filling to the neck of the carboy, but not always practical. I have tried both the CO2 purge and the technique of adding a minimum sugar addition to allow new fermentation to create CO2 - and hoping that bubbling activity would provide a barrier between the beer and air. Or does the immediate application of an airlock trap the "air" causing it to mix homogeneously into the producing CO2 until the pressure begins to expel gas through the airlock?
Yes, occasionally I get oxidized beer. Sucks. Happens less and less the better care I take in handling.
I just read back through this and not sure I made a whole lot of sense. Perhaps I answered my own questions by assuming that we need to treat beer delicately through any transfer or exposure to air (or better in a sealed environment under pressure), and that most serious oxidation occurs when wort/beer is splashed or agitated (oxygenation by mechanical means), and natural aging oxidation occurs as O2 transfers through plastic, wood and or metal by passive means. It seems both can be addressed by proper processes and proper handling and storage, minimized but never completely avoided.
OP
OP
This is an interesting concept to me. I have always thought of oxidation as 100% bad. So do you think preventing a barleywine from getting any oxidation might effect the flavor profile negatively? Traditionally brewers did not know the science behind brewing as much as we do today and the styles we know and love today reflect their processes. So might we, by protecting certain styles too much, deviate from the spirit of the style?
dyqik
Well-Known Member
I didn't mean that the bound up oxygen is the key to the taste, but that some oxidation is part of the taste of English cask beer, and the beer improves from it for maybe a day or so from the first beer being drawn out of the cask (the beer is brewed for cask serving, remember, so some oxidation products are part of the desired character), before it starts to spoil. When that oxidation happens it will use up some of the oxygen in cask. If only a small amount is admitted or present at filling or tapping and the vessel then sealed and/or backfilled with CO2, then oxidation will only go so far, and no further, because all of the oxygen present has been bound up in the oxidation products, and you can continue to store the beer in that state for some time without spoilage. The oxidation is only going to worsen with time if there is too much oxygen present, or if there is a continuous source of oxygen (or possibly if the oxidized compounds catalyze a different reaction that spoils the beer without additional oxygen). With a cask breather backfilling the cask with CO2, cask beer can be stored and served after tapping (which introduces some oxygen) for a month or so at cellar temperatures without significant change, if not much longer, despite the small amount of oxidation that will have occurred.
No, I think you still have to do everything in your power to prevent oxidation- as the oxidation you taste in long-bottled beers comes from the minute oxidation at bottling that gets more noticeable and stronger with time.
As an example, my neighbor gave me "plum brandy". I know it's not beer- but its the best example I have! Anyway, he made it 25+ years ago, as a high ABV plum wine. He forgot about it for at least 15 of those years, and then gifted us with a bottle about 3 years ago (the last one). Well, it wasn't actually a bottle of wine like you'd think of it- more like a jug!
This "plum brandy" is great! It's brownish in color, sherry notes predominate, and it has a sweet brandy-like finish. It's because the wine is greatly oxidized- the brown color, the sherry/madieria notes, the "brandy" finish- all point to oxidation.
The oxidation is technically a flaw- but it's awesome in this after dinner drink. I've shared this with some HBT forum members (we still have half a jug!) like Homercidal and Pappers (I think Pappers) and many others- and they could tell you what they think- but it's definitely an after-dinner sipper like cognac would be.
One of the interesting things I've noticed about oxidation is that it seems to affect some ingredients differently. For example, oxidation in a beer with roasted grains (say, an ESB or a stout) tends to be metallic in nature. In a beer with dark crystal malts, it seems to have that "sherry" flavor. That's a generalization, of course, but it's something I've noticed over the last 7 or 8 years of beer tasting/judging.
Ask and yee shall receive http://www.mocon.com/pdf/optech/Closures - Oxygen Passage Study.pdf the better bottle guys did a pretty serious look at closures for carboys.
OP
OP
Thanks! Good grief, those carboy cap "toppers" leak like a sieve.
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