Bubbles!

[bumab]

If there's any beer drinkers out there, you've probably noticed that tap beers can use two different gases for carbonation. Most use CO2, and some, notably Guinness, use N2. Lots of stouts are starting to use nitrogen as well.

 

Nitrogen gives smaller, more persistent bubbles. Why? I assume they last longer because they are smaller- less volume for the surface tension to hold in. But why are nitrogen bubbles smaller then carbon dioxide bubbles?

[Fishteacher73]

Possibly the geometry of CO2 molecule creates a larger spherical object. Just a guess.

Perhaps a CO2 molecul has dipole moments that cause momentary ionic bonds with other constituants of the beer and N2 does not...

 

None the less Guiness is right so the rest of the world just needs to figure it out and fall in step. (With possible exception of some British bitters...)

[bumab]

Could it have anything to do with the higher partial pressure N2 has in the atmosphere? So, N2 would come out of solution slower then CO2?

[Biochemist]

If there's any beer drinkers out there, you've probably noticed that tap beers can use two different gases for carbonation. Most use CO2, and some, notably Guinness, use N2. Lots of stouts are starting to use nitrogen as well.

I think this is because nitrogen is far less soluble in water than carbon dixide (I think it is about 50x less). Hence, the "big" co2 bubbles that appear in beer are coming out of solution, and self-aggregate into larger bubbles as they condense on each other. When you let a nitro pressured beer out of the tap, you get a mix of beer and nitrogen, but much less of the nitrogen is dissolved in the beer. This means there is less dissolved nitrogen to come out of the beer (for the same fill pressure), and less opportunity for the bubbles to aggregate.

 

It also means there is less flavor/distraction from gas in the beer, because there is less gas overall dissolved. You might have noted that Guiness tastes/feels less "bubbly".

 

This is pretty much the same reason SCUBA divers get the bends from nitrogen bubbles. Nitrogen is lowest solubiity of the major air gasses (N2, O2, CO2) and nitrogen comes out first when you decrease pressure (by surfacing).

[TeleMad]

Perhaps a CO2 molecul has dipole moments that cause momentary ionic bonds with other constituants of the beer and N2 does not...

 

A CO2 molecule has a 0 dipole moment: it's nonpolar. It's a linear molecule: O=C=O, with no lone pair electrons on the central atom: so the two polar carbon-oxygen bonds exactly cancel each other's affect.

 

An N2 molecule also has a 0 dipole moment. It's a homonuclear diatomic molecule.

[Qfwfq]

Possibly the geometry of CO2 molecule creates a larger spherical object. Just a guess.

At normal temperature and pressure, I don't think either of the two gasses deviates all that strongly from PV = nRT. IOW the molecule doesn't count much. Solubility and surface tension, possibly along with partial pressure in the air, would be the determining quantities but I haven't worked it out.

 

One thing, as they say, Guinness is good for you! ;)

[bumab]

Solubility and surface tension, possibly along with partial pressure in the air, would be the determining quantities but I haven't worked it out.

 

Since the partial pressure of CO2 is so much lower, wouldn't that mean it would come out of solution much faster then N2? That would make for the smaller bubbles, as well as the reason CO2 gas bubbles out so much faster.

 

One thing, as they say, Guinness is good for you! ;)

 

Meal in a glass!

[Biochemist]

At normal temperature and pressure, I don't think either of the two gasses deviates all that strongly from PV = nRT.

Agreed.

[Biochemist]

Since the partial pressure of CO2 is so much lower, wouldn't that mean it would come out of solution much faster then N2? That would make for the smaller bubbles, as well as the reason CO2 gas bubbles out so much faster.

Atmospheric pCO2 has only a small effect on formation of CO2 bubbles from solution. Overall pressure is the major driver. If you reduce pressure on the beer but still leave the atmospheric gass as 100% CO2 (as it was in the keg) you still get a similar rate of CO2 effusion from the liquid.

 

Likewise, with N2. The difference is that there is 50x more CO2 in solution than N2 at the same pressure and temperature. Ergo, there is a lot more gas to come out of solution.

 

Also, British pubs tend to serve beer slightly warmer than American pubs. If an American pub servies nitro-laden beer warmer than their CO2 laden beer, the amount of dissolved gas decreases even further. Ergo, the dissolved gas differential would be more like 100x than 50x, with cold CO2 having a far higher solubility than warmer N2.

 

Qfwfq's point about surface tension may be valid as well, particularly with respect to the extraordinary retention of the small-bibble-head on the Guiness, but I can't comment intellligently on that.

 

But I sure do like Guiness. Although I REALLY think that their attempts to put draught Guiness in a can/bottle with little nitrogen-source containers don't work well. They are pretty disappointing. It does, however, make a cool noise when the little cannisters erupt inside the bottle. ;)

[Biochemist]

Meal in a glass!

I can only assume you actually meant "pitcher".

[Qfwfq]

I can only assume you actually meant "pitcher".

At the pub, a half pint of beer is called a glass! It is served in a glass, without a handle.

[Biochemist]

At the pub, a half pint of beer is called a glass! It is served in a glass, without a handle.

Sorry, Qfwfq. I was speaking American, and implying that no real Guiness afficionado would order only a pint. One would order a pitcher, which is typiically about four pints, and typically costs a little bit less.

[bumab]

Of course! Around here, our pitchers are made from glass. It's a really big glass. ;)

[Qfwfq]

Try a Dublin pub, you order either a pint, which comes usually in a mug with a handle, or a half pint which comes in an odd, tall slender chalice having a short stocky stem and a slightly widening rim like a horn. Usually. Pints and half pints give more chance for each person in a group to pay a round or two.

 

In an Irish pub you can cuss all you like, they think you're a right nerd if you don't, unlike in English pubs.

 

In Kinsale I was told the story of when an Englishman acquired one of the many pubs. First few customers in, and a guy walks up to the counter and says "Gimme a f***kin' Guinness.", and the Englishman gapes at him and says "Out!", pointing the way, like they'd do in any English pub. Everybody present turned and stared, and the Englishman pressed the point: "Out of my pub!". At that point, every customer present synchronously rose and they all trooped out. Nobody walked in untill the management had again changed!

 

In one Kinsale pub hangs an olde style sign saying "No Bloody Swearing". I was told it was hobbled from an English pub and hung there for the laugh.

[FREYA021]

A CO2 molecule has a 0 dipole moment: it's nonpolar. It's a linear molecule: O=C=O, with no lone pair electrons on the central atom: so the two polar carbon-oxygen bonds exactly cancel each other's affect.

 

An N2 molecule also has a 0 dipole moment. It's a homonuclear diatomic molecule.

corecct my friend. i am chemist and also am scuba diver, u have something called drunkness of deeps, it means scubadiver got lot of N2 disolved in the blood, ofcourse cos of preasure... when we r going to the surface we must make stops, to let it get out as a gas as preassure is decreecing... ok its underwhater story, what with a beer?

CO2 is well solubile in whater, u must know that ppl who have flowers let the whater to stay over night in tanks... its healthier for flowers they say. U know why? u must guess cos of CO2, corecct. cos CO2+H20 forms H2CO2 very unstable acid... more is like HCO2minus, it must cange taste of beer to. must be more acid... also free elctron pairs on oxigens in that ion can take part in forming whaterbonds with whatr molecules in beer, what means that it gets dipolar moment! all that can and i am sure does efect on bubbles...

[bumab]

Try a Dublin pub....

 

Do they make a little clover in the head over there? I thought that was a little wierd and hokey, but a couple pubs over here do.

[Qfwfq]

Clover? First I hear of that. Blasphemy, I tend to think!