Re: Super Cold Beer!

["Daniel L. MacIsaac" <Dan.MacIsaac@NAU.EDU>]

> 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.
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).

Bubbles grow as they rise in a beer glass because they collect dissolved
CO2 molecules which are moving too fast to stick together.  Beer IS a
supersaturated CO2 solution (at least as far as I understand the chemistry)
where CO2 molecules want to escape by forming bubbles but have too much
KE to cling together without a seed of some sort.  Given the opportunity
to contact any macroscopic seed bubble they will do so and start a bubble
or accrete one that exists.  Salat or sand particles alone will seed the
heterogeneous nucleation of bubbles in beer, but they work much better
if they have air bubbles already clinging to them.

Beer bubbles will expand (and accelerate)  as they rise through beer
by acquiring dissolved CO2 by accretion (pressure-change expansion is
inconsequential).  Beer bubbles speed up and increase in size as they
rise from nucleation sites on the glass sides or bottom (don't take my
word for this observation -- do the research :^).

Other related quips on this topic:

Beer bubbles ARE heterogeneous nucleation, as are clouds according to
Bohren; clouds can even nucleate on ions.  This is after Bohren's popular
literature pieces, not his scientific peer-reviewed pubs which I've never
read.  I would be delighted to have anyone knowledgeable on these topics
inclrease or straighten out my understandings of these phenomena, which are
pretty neat conversation topics.

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.

The beer widget is in the bottom of Guinness and Murphy's draft cans (at
least after my research).  The Guinness beer widget is briefly described
online at
http://www.nano-technology.com/i-world/nprods3.htm
most of the
way down that document.  Aka the "Guiness - Enigma Lager Widget ", this
device supposedly cost 11MPounds to develop and requires liquid N2 to
pressurize.  It is pressurized with CO2 and N2.  All that technology just
to improve my personal beer-drinking pleasure.  Life is good.

Dan M

Dan MacIsaac, Assistant Professor of Physics and Astronomy, Northern AZ Univ
danmac@nau.edu          http://purcell.phy.nau.edu         PHYS-L list owner