Re: Super Cold Beer!

[William Beaty <billb@ESKIMO.COM>]

On Thu, 1 Jul 1999, Daniel L. MacIsaac wrote:

> I am out of my depth here.  I'll try reading more and asking about before
> speculating further...

Me too, mine is just speculation based on informal observations.  Having
played with beer bottles and microwaved coffee, I have suspicions that
usually tiny bubbles are the "nucleation sites", and that solid particles
usually are not.


> I can break the beer bottles easy (water in a Corona bottle, fill to bottom
> of neck, use leather gloves & hold over a trash can; bottom usually comes
> out as a nice clean disk) but this requires --as you noted-- a fairly large
> movement of 5-10 cm to leave the water behind and make the vacuum.
>
> The beer foaming seems subtler; it requires a small (1mm?) blow (like a hard
> toast clink) on the top of the bottle.  The pressure waves must travel as
> you describe, and I agree the bubbles come upwards, foaming the beer. But
> I don't see the mechanism where the pressure wave nucleates the bubbles,
> and would like to...

Maybe I'm wrong, but I was under the impression that the value of CO2
saturation in water varies with pressure.  If this is true, then we can
make gas start coming out of solution by lowering the pressure.  If we
*really* lower the pressure, then maybe we can trigger "homogeneous"
nucleation and create tiny bubbles.  If the liquid is far enough from
equilibrium, then new bubbles will form because of ions and dust motes.  I
think this is how bubble chambers work: suddenly lower the pressure of the
liquid hydrogen, and any ions in the liquid become the nucleii for
bubbles.  Water is full of ions.  Maybe if we lower the pressure of beer
suddenly, we can cause the ions to nucleate the CO2 bubbles.  Gently
whacking the top of the bottle might create enough new bubbles.

I don't understand the bottle-bottom cavitation very well.  If I whack the
bottle hard, and the bottle moves downwards, why doesn't this cause
cavitation to arise all through the liquid?  Or maybe it does, now that I
think about it.  I've always assumed that one large cavity opens up at the
bottom of the liquid.  Maybe I'm wrong, and many cavities open up
throughout the volume; just the same as bubbles which appear during
boiling in a vacuum.  On the other hand, maybe the sound wave of the
"clink" is very small in physical extent.  If the sound wave in the liquid
was very thin, then it's peak negative pressure would be huge, and it
could nucleate new bubbles on ions, proteins, etc.





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