Purpose of N2 in Head?

Discussion in 'General Home Brew Equipment Discussion' started by ssashton, Nov 9, 2019.

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  1. Nov 9, 2019 #1

    ssashton

    ssashton

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    Hi everyone,

    I'm curious about getting a Guinness-like head on some beer.

    Firstly Ive already read that N2O nitrous-oxide is not what is needed but rather pure N2 nitrogen.

    I'm a bit confused, because I have read that nitrogen is basically not water soluble and so the purpose is not to make beer fizzy, but simply to provide serving pressure for tap lines with low carbonation beer and the head comes from feeding the beer through a diffuser plate.

    However the Guinness draft cans have a widget in them which I believe is N2 and there is certianly no diffuser plate! Same with John Smiths type beer. Yet they still achieve creamy stable head.

    So something doesn't add up for me. What's the real story here?? What does N2 contribute to stable small bubbles head?
     
  2. Nov 9, 2019 #2

    Clint

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    Dunno...I've had great results using flaked barley...with wheat or oats it both!
     
  3. Nov 9, 2019 #3

    Drunkula

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    Nitrogen bubbles are smaller than carbon dioxide bubbles and make the head more tight and creamy. The widget has a tiny hole in it and when you open a can the pressure drops and the widget squirts out beer and that acts just like a diffuser plate. Guinness came in and did a talk on it at uni. They brought loads of cans to giveaway Somebody in the faculty got quite annoyed when we all swooped on it at the end as he thought he was going to hoard the lot. ha ha.
     
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  4. Nov 9, 2019 #4

    ssashton

    ssashton

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    Oh I see! I had always thought the widget contained gas, but I see now.

    So presumably the N2 does dissolve in beer, even if less than CO2? If not the gas would just escape and the beer would be flat.

    Does N2 need to be at far higher pressure? Is that how they get it dissolved? If so, what kind of pressure are we talking?
     
  5. Nov 10, 2019 #5

    Zephyr259

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    It's a gas mix that's used, not pure nitrogen, think 70:30 N2:CO2 is the usual, so the mild carbonation is from the residual CO2.
     
  6. Nov 10, 2019 #6

    simon12

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    Guiness gas or G mix is 25/75 (25% CO2 75% N2) and its served at higher pressure (30-40psi) through a specially designed tap. John Smiths I think would be similar or exactly the same, Guiness being thicker traps the N2 bubbles longer and produces its head while John Smiths being thinner goes very flat very fast as the N2 leaves.
     
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  7. Nov 10, 2019 #7

    ssashton

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    Great info thanks! I have to believe the N2 is absorbed otherwise it would not effect bubble size. Presumably the fact N2 is not so water soluble as CO2 is offset by the higher pressure.
     
  8. Nov 10, 2019 #8

    foxy

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    Get yourself a syringe, suck up a little beer and some air and squirt it back into your beer, air is 78% nitrogen and give yourself a nitro pour, be careful though.
    I did read Guinness used to give out syringes for such a feat.
     
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  9. Nov 11, 2019 #9

    ssashton

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    Cool! 20191111_164330.jpg 20191111_164542.jpg
     
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  10. Nov 11, 2019 #10

    Northern_Brewer

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    The physics of gas mixtures can get complicated but you're talking about two separate things here.

    Guinness and other nitro beers rely on the fact that nitrogen forms small bubbles to so use a 30/70 mix (CO2:N2) - ie mostly nitrogen. If you used pure nitrogen it would be like a Mr Whippy.

    Traditionally your typical lagers were served with just CO2. The trouble is that if your cellar is a long way from the bar then you need to increase the pressure of CO2 to "push" it to the bar to the extent that your beer ends up being pure froth as it has so much CO2 in it - and more acidic as some of it dissolves to form carbonic acid. You can either install a pump or dilute the CO2 with a bit of nitrogen as an inert "carrier" gas. So something like 60/40 ("beer gas") allows you to use a higher pressure in your keg lines, but the beer ends up with 40% less CO2 in it than if you used pure CO2.

    So you get different results with 30/70 gas than 60/40.
     
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