Re: Super Cold Beer!

[William Beaty <billb@ESKIMO.COM>]

> Dan M wrote:
> > You might check out "Clouds in a Glass of Beer: Simple Experiments in
> > Atmospheric Physics" by Craig Bohren (should be <$20 from Amazon), which is
> > a delightful read on this sort of thing.  Bohren distinguishes heterogeneous
> > nucleation (where something else nucleates the cloud) from homogeneous
> > nucleation (where the molcules are cooled enough to "stick" in their
> > collisions
> > and nucleate themselves.  You get heterogeneous nucleation on the insides
> > of the beer glass or from salt or sand (uck) particles in beer.


I think I just discovered a "scientist urban legend".  While trying to
superheat water in a microwave oven (so it "explodes" when sugar hits it),
I saw evidence that the boiling is triggered by tiny bubbles.  I discussed
this with some people, and they universally insisted that it was the sharp
edges of the sugar grains which trigger the boiling.

When we put salt in beer, what causes the foaming?  Is it the sharp edges
of the salt?  Is it the sudden change in salinity?  Or, is it the films of
air that cling to the salt crystals as when they are submerged?  How could
we discover the source?  One way would be to use wet salt (no films of
air.)

1. Put some salt in a tablespoon of beer.  Use enough salt that there are
   plenty of solid crystals remaining.  Wait a moment until the fizzing
   stops, then dump this into a glass of beer.  This triggers much
   fizzing.   Wet salt causes beer to fizz.

2. Put some salt in a tablespoon of beer.  Use enough salt that there are
   plenty of solid crystals remaining.  Wait a moment until the fizzing
   stops, then dump some of the liquid into the beer (take care not to
   dump any solid salt.)  This STILL triggers much fizzing.  Huh?  The
   liquid from wet salt can cause beer to fizz?  Maybe there are tiny
   bubbles in the liquid!

3. Put some salt in a tablespoon of beer, then wait for about 1/2 hr.
   Skim off the white scum that collects on the spoon (yep, there were
   tiny bubbles in the liquid!)  Dump spoon of beer/salt into a fresh
   glass of beer.  This *doesn't* trigger fizzing.  Wet salt alone isn't
   enough to make the fizz.

4. Pour some hot tap water into a spoon.  It looks misty because it's full
   of tiny bubbles.  Dump it into beer.  FOOOSH!  Tiny bubbles can trigger
   "beer explosions".

Tenative conclusion: it's the air on the salt-crystal surfaces which
triggers the fizzing, and not the salt itself.  This makes sense.  Tiny
bubbles will behave as "seed bubbles", and if a large number of them are
released into a carbonated beverage, each one can fill with CO2 and grow
enormous.  Same thing happens with superheated water.  Heat a mug of water
for a long time in the microwave oven, then dump in some sugar (or a spoon
full of hot tap water).  There is a explosion of boiling.

Hey, this explains something I wondered about as a kid.  If we mix milk
into root beer, there is no foam, but if we use ice-cream, there's lots of
foam.  But ice cream would be like solid ice if it wasn't for the billions
of tiny bubbles in it.  Ice cream is like frozen whipcream.  It's the
bubbles which trigger explosion when ice cream hits warm root beer.

And so I go to the fridge, find no ice cream but DO find whip cream and
cola.  I dilute some whip cream with water, mix it well so it resembles
milk, then dump it into a half-glass of diet coke.  FOOOOSH!  Big mess all
over the countertop.  The whipcream is full of extremely tiny nitrous
oxide bubbles, and these act as seeds for the foam explosion.  Milk
doesn't do this, but whipped cream does.



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William J. Beaty                                  SCIENCE HOBBYIST website
billb@eskimo.com                                  http://www.amasci.com
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