The great nitrogen bubble debate

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choosybeggar

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Ok, maybe there is no great debate but what the hell. We've all heard and digested the explanation of nitrogen beer's tiny cascading bubbles and contribution to creamy mouthfeel.

I first leaned the "science" of nitrogen bubbles from Cecil Adam's Straight Dope column and have been repeating this notion (which I now believe to be flawed). To wit, according to the column:

"From my online reading I learned that the secret of Guinness's creamy mouthfeel, as the taste experts put it, is a mix of nitrogen and carbon dioxide rather than pure CO2 as the bubblizing ingredient. Nitrogen bubbles are much smaller than CO2 bubbles, a mere 50 microns in diameter, and produce a smoother head. But nitrogen doesn't produce bubbles as spontaneously as CO2. At the corner tap they deal with this by using a special nozzle that aerates the stout with nitrogen as it's poured."

But of course, what is ignored is why the hell is CO2 needed at all in this mix? And why aren't there mixed populations of little nitrogen bubbles and large CO2 bubbles?

Here's what I now believe. CO2 is needed because the foam consists of CO2 bubbles. The bubbles are small because of the manner in which they are formed (by jetting the beer through tiny apertures). The role of Nitrogen is to provide the driving force (in other words, 6 PSI of Co2 would do a piss poor job of driving beer through a stout faucet). I've tried carbonating with pure CO2 then connecting beer gas and the beer pour perfectly right away without time for the equilibration of nitrogen gas in solution?

Your thoughts?

Link to Cecil Adams' Guinness column:http://www.straightdope.com/columns/read/1368/why-do-the-bubbles-in-guinness-stout-float-down
 
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choosybeggar

choosybeggar

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Oh yeah, I forgot one thing. Has anyone ever tried no Co2? I use beer gas so it's formally impossible. But I'm betting straight nitrogenated beer poured through a stout tap will have minimal foam.
 
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Here's what I now believe. CO2 is needed because the foam consists of CO2 bubbles. The bubbles are small because of the manner in which they are formed (by jetting the beer through tiny apertures). The role of Nitrogen is to provide the driving force (in other words, 6 PSI of Co2 would do a piss poor job of driving beer through a stout faucet). I've tried carbonating with pure CO2 then connecting beer gas and the beer pour perfectly right away without time for the equilibration of nitrogen gas in solution?
What you say above is what I accept as fact regarding the concept. I've seen a lot of supposed "facts" about nitrogen having a stabilizing effect on foam, but the fact is that almost none of it dissolves. Nitrogen is around 100 times less soluble in water than CO2. So, nitrogen simply provides the "oomph" without additional effervescence, while CO2 provides the bubbles.

I've proven the concept to an extent by using argon in place of nitrogen when serving through my stout faucet. The pour is exactly as you'd expect with nitrogen. When I do that, I do not mix the gas. I carbonate to a low level, then push with pure argon.

What I have not done is a side-by-side comparison of the same beer pushed through a stout faucet with CO2, beer gas, nitrogen, and argon. It'd be an expensive test but definitely worth doing in the name of proper science.
 

Gavagai

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According to George Fix (Principles of Brewing Science, 2nd edition, p. 172):

CO2 is needed to maintain the equilibrium pressure of the beer (i.e., keep it at the desired level of carbonation). The reason that nitrogen produces a more stable foam is that a 75% nitrogen mixture is nearly in equilibrium with the air around it. Hence, there is a very small partial-pressure differential for nitrogen, and, since the amount of CO2 is reduced by 75%, the partial-pressure differential of CO2 is likewise reduced by 75%. In short, nitrogen-CO2 bubbles are much closer to being in equilibrium with the air than straight CO2 bubbles, because the air is mostly nitrogen.
 
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Though more believable, that still sounds a bit hokey to me. The bubbles in the beer's head are produced almost entirely by CO2 coming out of solution. The composition of the gas inside those bubbles is not 75% nitrogen, by virtue of nitrogen's low solubility. Only the gas in the keg's headspace is 75% nitrogen. I would very much like to see further research and experimentation on the topic.
 
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choosybeggar

choosybeggar

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Gavagai said:
According to George Fix (Principles of Brewing Science, 2nd edition, p. 172):

CO2 is needed to maintain the equilibrium pressure of the beer (i.e., keep it at the desired level of carbonation). The reason that nitrogen produces a more stable foam is that a 75% nitrogen mixture is nearly in equilibrium with the air around it. Hence, there is a very small partial-pressure differential for nitrogen, and, since the amount of CO2 is reduced by 75%, the partial-pressure differential of CO2 is likewise reduced by 75%. In short, nitrogen-CO2 bubbles are much closer to being in equilibrium with the air than straight CO2 bubbles, because the air is mostly nitrogen.
I've heard that one and I formerly believed it. Now my belief is that a foam consisting of smaller CO2 pockets (a stout tap foam) is inherently more stable than one comprised of larger bubbles (for example, those forming spontaneously on the asperities of your beer glass).

Two lines of reasoning proffered so far in this thread refute the concept of concentration gradient-dependent foam stability. First, when I lightly carbonate a beer then hook up beer gas, immediately the beer pours perfectly, without an interval for nitrogen gas to equilibrate in the beer. Secondly, and more convincingly, is Yuri_Rage's observation that argon pressurized lightly carbonated beer pours identically to nitrogen-pressurized beer. Given there is virtually no argon in the atmosphere, the pressure gradient is ginormous. Yet, the foam is stable.
 

Mike37

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I just did some non scientific experimenting with a stout faucet on 100% co2. I was indeed able to get the super dense "Guinness head" bubbles that you could scoop up with a spoon like pudding.

Now, it didn't stick around for more than a minute or two, but that's a product of the beer. This was just a blonde ale with zero head retention ingredients and not much head retention capability out of a regular faucet.

The key is low carbonation with sufficient pressure to overcome the stout faucet's restrictor plate. I strongly believe nitrogen contributes very little to nothing except for that required pressure.
 

StMarcos

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Couldn't the N2 get 'mixed' in with he beer during the pour? Meaning, couldn't the bubbles have a significant N2 content even though it wasn't initially dissolved in the beer to any significant degree?

I would have to guess that the smaller bubbles are a direct result of the restrictor plate in the faucet. The velocity of the beer knocks the growing bubbles off when they are small. With a standard beer, the size of the bubbles is much larger because they are nucleating on the glass, and are allowed to grow much larger by the time buoyancy frees them from the glass.
 

daft

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According to George Fix (Principles of Brewing Science, 2nd edition, p. 172):

CO2 is needed to maintain the equilibrium pressure of the beer (i.e., keep it at the desired level of carbonation). The reason that nitrogen produces a more stable foam is that a 75% nitrogen mixture is nearly in equilibrium with the air around it. Hence, there is a very small partial-pressure differential for nitrogen, and, since the amount of CO2 is reduced by 75%, the partial-pressure differential of CO2 is likewise reduced by 75%. In short, nitrogen-CO2 bubbles are much closer to being in equilibrium with the air than straight CO2 bubbles, because the air is mostly nitrogen.
That is echoed by the lecture series "The Brewmasters Art" which I think is available from audible.com. But the speaker (with endless awards and such, as you can hear from their sample) furthermore emphasizes a key point on why nitro bubbles have a disproportionate effect. Nitro bubbles do not cannibalize each other like co2 ones do. Small co2 bubbles adjacent to a large one get sucked into the large one thru the bubble interface... the small disappear into the large, which eventually pops.

Oh, here it is http://www.learnoutloud.com/Audio-Books/Science/-/The-Brewmasters-Art/34208
 
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Nitrogen will not get mixed into solution via pour turbulence because it gets forced into solution at the beer surface inside the keg (at a much lower rate than CO2), and the beer is drawn from the bottom of the keg. There is no turbulent interface in a nitrogen rich, pressurized environment.

My hypothesis is that small, dense foam is inherently more stable than large, loosely packed foam, regardless of gas composition. I am all but convinced that the bubbles are comprised almost entirely of CO2 that has been forced out of solution via the restrictor plate (i.e., little to no nitrogen content within the foam). I wish I could accurately test the nitrogen absorption in a beer gas system in order to further prove the theory. These discussions about nitrogen bubbles, while seemingly scientific, also seem to violate physics.

I do agree that the partial pressure of CO2 keeps the beer carbonated, though I have experienced success serving force carbonated beer for up to 3 weeks on pure argon alone without any need for reintroduction of CO2 to keep the pour consistent. I also agree that the lower carbonation and fine foam texture contribute to a different mouthfeel with less carbonic bite. I simply disagree that there is any significant nitrogenation happening.

Perhaps someone could design an experiment wherein beer carbonated to about 1.2 volumes is physically forced through a restrictor plate with no introduction of gas, be it nitrogen or otherwise. I'm suggesting a mechanical serving system for the purpose of showing that CO2 based foam is indeed stable. That pour could become the control in an experiment utilizing pure nitrogen, pure CO2, and beer gas for storage and serving. Pour each beer several times over the course of about 2 weeks, with the temperature and pressure of each keg kept stable throughout (except the CO2 keg, which would have to be dialed back for storage, lest it become overcarbonated). Note any differences.
 

Jsslack

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The way i understand it, the head would be almost entirely CO2 unless the nitrogen was introduced at the faucet. This is the only scenario i can see that would introduce N2 by turbulence. This is not the case though, instead N2 is used as propulsion, pushing the beer through the line. I would assume, from personal experience, that a beer with lower volumes of CO2 would naturally produce a more stable head.

In order to maintain a low carbonated beverage and still be able to push it through a 10ft plus long line, at a reasonable rate, a gas that is less soluble must be used.
 
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choosybeggar

choosybeggar

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Yuri_Rage said:
Perhaps someone could design an experiment wherein beer carbonated to about 1.2 volumes is physically forced through a restrictor plate with no introduction of gas, be it nitrogen or otherwise. I'm suggesting a mechanical serving system for the purpose of showing that CO2 based foam is indeed stable. That pour could become the control in an experiment utilizing pure nitrogen, pure CO2, and beer gas for storage and serving. Pour each beer several times over the course of about 2 weeks, with the temperature and pressure of each keg kept stable throughout (except the CO2 keg, which would have to be dialed back for storage, lest it become overcarbonated). Note any differences.
I think your observations with argon accomplish effectively the same thing as a purely mechanical system: it clearly can't be nitrogen in the foam and there can't be a diffusion gradient effect contributing to foam stability. I say case closed. :)
 
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I think your observations with argon accomplish effectively the same thing as a purely mechanical system: it clearly can't be nitrogen in the foam and there can't be a diffusion gradient effect contributing to foam stability. I say case closed. :)
I'd like to agree, but SO many texts cite nitrogen as a key player in foam stability. I would like to refute them outright with a well designed and executed experiment. I currently lack the means to do so, and I do not foresee buying the requisite equipment to do a side-by-side comparison.
 

cscade

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It was explained to me by a brewer I highly respect (though who is not a scientist) that the purpose of beer gas is to allow higher faucet pressures without excessive carbonation for the style. He stated that a negligible amount of nitrogen was ever dissolved in solution regardless of serving time. Therefore, by his description, the purpose of the nitrogen is entirely functional, and is actually intended not to interface with the finished beverage.

This makes perfect sense to me, and I believe the bubbles in a beer poured through a stout tap and pushed with beer gas are just full of CO2.
 

mattd2

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I'd like to agree, but SO many texts cite nitrogen as a key player in foam stability. I would like to refute them outright with a well designed and executed experiment. I currently lack the means to do so, and I do not foresee buying the requisite equipment to do a side-by-side comparison.
What about the standard method of cranking up the CO2 to 30 PSI on a stout tap during the pour then purging back to carb pressure (for those that don't have beer gas).
My one concern about the argon experiment/argument is that it could be argued that the argon is replacing the nitrogen (I would bet you would get that, with no reasoning for it, from the the-bubbles-are-nitrogen crowd).

Also why is anyone believing someone who uses the term "bubblizing ingredient" when trying to "scientifically" explain the reason.
 

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If you scooped some foam into a bottle to fill it completely to the top, introducing a bit of degassed water into the bottom, sealed it, waited, and checked the pH of the water, maybe you could get an idea of the composition of the gas?
 

Die_Yankees_Die

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If Nitrogen is ONLY used as a pushing "umph", then why does nitro-tapped guiness and the like have that famously creamy, smooth head as opposed to just spitting out flat beer?
 
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choosybeggar

choosybeggar

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Die_Yankees_Die said:
If Nitrogen is ONLY used as a pushing "umph", then why does nitro-tapped guiness and the like have that famously creamy, smooth head as opposed to just spitting out flat beer?
Explained in the thread. Small bubble foam consisting of CO2 =creamy smooth head
 
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choosybeggar

choosybeggar

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Yuri_Rage said:
I'd like to agree, but SO many texts cite nitrogen as a key player in foam stability. I would like to refute them outright with a well designed and executed experiment. I currently lack the means to do so, and I do not foresee buying the requisite equipment to do a side-by-side comparison.
I'm scientific but not engineering minded. If someone could design plans for a piston device to push beer through a stout tap, I be interested in making one, performing experiments and publishing. Fun!
 

mattd2

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If Nitrogen is ONLY used as a pushing "umph", then why does nitro-tapped guiness and the like have that famously creamy, smooth head as opposed to just spitting out flat beer?
Because it is not hooked up to nitrogen - it is a 25:75 blend (usually) of CO2 Nitrogen. The beer is still carbonated with CO2 but the blend gas allows for the head pressure to be higher without overcarbing the beer.
I'm scientific but not engineering minded. If someone could design plans for a piston device to push beer through a stout tap, I be interested in making one, performing experiments and publishing. Fun!
Beer engine with a hose attached... now you just got to drop the $100-$200 on a beer engine :D
 

Wynne-R

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I was once served a Guinness that had a small head but was completely flat. Weird. It turns out the regulator was bad and there was zero pressure on the CO2.
 

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I'm scientific but not engineering minded. If someone could design plans for a piston device to push beer through a stout tap, I be interested in making one, performing experiments and publishing. Fun!
I'm picturing a bike pump where instead of pulling in air you have it submerged in beer. it might be a waste of beer, though, so not sure if it would be worth it, but there might be a way of getting the beer into the inlet without fully submerging it.
 

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It seems like you could test this in a straightforward manner by having a bladder inside a keg. If the beer was carbed to a normal level, and then placed in the bladder, you could pressurize the outside of the bladder with high pressure to get a similar effect without any gas exchange. If the results are the same as beer gas, then the nitrogen doesn't play a role. Any takers?
 
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choosybeggar

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zymurph said:
It seems like you could test this in a straightforward manner by having a bladder inside a keg. If the beer was carbed to a normal level, and then placed in the bladder, you could pressurize the outside of the bladder with high pressure to get a similar effect without any gas exchange. If the results are the same as beer gas, then the nitrogen doesn't play a role. Any takers?
The only bladder I typically associate with beer is my urinary bladder :)

Sounds like a possibility. Any specific instructions/product recommendations? Assuming I use a corny keg, how would one differentially carb the beer versus inflate the bladder.
 

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Yeah, the nitrogen may or may not (I suspect not) play some minuscule role in the head formed through a stout faucet, but for all intents and purposes it is there purely to provide extra pressure. For evidence, all we have to do is look at history.

The modern stout faucet was created out of a desire to replicate, with a keg system, the creamy head found on cask beers poured with (as some have mentioned) a beer engine through a sparkler.

Simply put, the results (in terms of thick creamy head) are exactly the same.
 

iaefebs

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While you are looking into this I have a question. The bubbles that are forced back into the bottom of the glass are... I'm going to guess the nitrogen bubbles. As the CO2/ nitrogen pushes up through the bottom of the glass the space that empties is replaced by the beer which drags the nitrogen bubbles back down with it. So eventually you would have more nitrogen as the nitrogen bubbles keep recycling and CO2 escapes?
 

jhall4

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While you are looking into this I have a question. The bubbles that are forced back into the bottom of the glass are... I'm going to guess the nitrogen bubbles. As the CO2/ nitrogen pushes up through the bottom of the glass the space that empties is replaced by the beer which drags the nitrogen bubbles back down with it. So eventually you would have more nitrogen as the nitrogen bubbles keep recycling and CO2 escapes?
You're assuming there's going to be a lot of nitrogen. There's not. The only way nitrogen makes it to the tap is if it's absorbed in the beer - and very little is absorbed by the beer. Whatever small amount is absorbed in the beer surely forms bubbles but the cascading effect is caused by the restrictor plate forcing so much of the CO2 out of solution all at once and in such tiny bubbles. These bubbles rise much, much faster in the center column than around the edge of the glass, forcing the bubbles there back down.
 
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choosybeggar

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Yuri_Rage said:
Debate's over already? I expected a lot more resistance. ...and a lot more quotes from old books and marketing propaganda.
My feeling is that it's fairly obvious the conventional explanation doesn't fit that facts well. Until I began making nitro brews, though, I hadn't given it much thought.
 
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The concept is well explained in several posts, each with slightly different wording - that probably helps. Nice job with that. I was really happy to see the topic crop up.
 

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choosybeggar

choosybeggar

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Yuri_Rage said:
The concept is well explained in several posts, each with slightly different wording - that probably helps. Nice job with that. I was really happy to see the topic crop up.
No problema. You owe me a beer though :)
 

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Yuri_Rage said:
...marketing propaganda.
Nitro infused!!!!
Top secret gas blend!!!!
Cold brewed with nitrogen!!!!
Nitro filtered and served ice cold!!!!

Better? :)
 
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choosybeggar

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Mike37 said:
Nitro infused!!!!
Top secret gas blend!!!!
Cold brewed with nitrogen!!!!
Nitro filtered and served ice cold!!!!

Better? :)
And if the yeast came from a frozen stock, call it, "Nitro-Glycerine, really packs a wallop."
 

RickFinsta

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Just saw this - you could do the bladder experiment with a Party Pig. Just throw a sparkler or stout faucet on there and if the head is thick and creamy, then debate=over.
 

RickFinsta

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The bladder would need to generate sufficient pressure (~20 psi). It probably does not squeeze that much.
You could always drill a hole and throw an air fitting on there; my point was simply that an apparatus for bladder testing already exists and is relatively cheap (much less than a beer engine!).
 

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