Re: Super Cold Beer!

[William Beaty <billb@ESKIMO.COM>]

On Tue, 29 Jun 1999, Daniel L. MacIsaac wrote:

> As you observed, seeding with bubbles GREATLY helps, but bubbles CAN
> nucleate from solution by having dissolved CO2 molecules adhere
> to macroscopic particles or even microscopic particles (as I read
> the nonprofessional literature; I'm an interested amateur here).

True, but I'm now led to wonder if this only occurs when the liquid is far
from equilibrium, as when we hit the liquid-H2 in a bubble chamber with a
pulse of negative pressure, or when we pop the lid on a bottle of warm
beer.  If "homogenous" nucleation is immenent, then probably any
nonuniformity in the liquid will trigger the formation of a bubble.  On
the other hand, what if the liquid is only a little out of equilibrium,
e.g. after the beer has bubbled for a couple of minutes?  In this
situation, MAYBE the effect of the sand or the ions will be below the
threshold where bubbles are triggered.  If so, then the only way to
trigger a bubble is to inject a tiny seed-bubble.  (Bohren mentions that
bubbles which are below a certain diameter will shrink, and this
threshold-diameter depends on saturation.)


> I'd sure like someone to explain why beer bottles foam violently when struck
> sharply on the lip with the bottom of another bottle.  This one stumps me.

I think I have a solution.  If you take an unopened jar of spagetti sauce,
hold it in one hand while striking it sharply on the lid with your fist,
you will hear a loud "snap".  Sometimes the bottom of the jar will
shatter.  This is a cavitation effect: the jar moves downwards, but the
sauce does not, and so the pressure at the surface of the bottom of the
jar falls to zero and a vacuum-pocket briefly appears.  The pressure at
the top of the sauce then accelerates the sauce downwards, and when the
vacuum-pocket closes, there is a "water hammer" pressure pulse.

If we extend this idea to beer bottles, then we might predict that, when a
bottle is thrust violently downwards by being whacked by a descending
bottle, then the pressure at the surface of the bottom of the bottle will
experience a negative-going spike.  This might be enough to trigger
*homogenous* nucleation all over the bottom of the bottle.  That's the
very worst place to create a population of seed-bubbles, since they will
quickly grow and launch the contents of the bottle up towards the ceiling.


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