I am going on a climbing trip to Mexico in November, and we're
intending taking a half bottle of champagne to celebrate with when we
get to the top, if we manage it.

Two problems arise. The first is that champagne will freeze at
approximately the same temperature as wine (-5 or -6 degrees C), but
we think we can get around this by keeping it somewhere warm. The
second is that the lower air pressure may cause the cork to pop by
itself.

This is my question: At what altitude, temperature independent, will a
champagne cork spontaneously pop?

We're only climbing to 5600m, but I'd be interested to see the real
answer if it's higher.

Chris

Hi, Chris

In my view, the thing that holds the cork in place should retain the
cork in place until you are ready to go 'pop'.

Of course, once you remove the said 'thing', the cork could pop
spontaneously even down at Sea Level.

But half-a-bottle?

I could knock that back myself in no time.

I suggest that you take at least a dozen bottles along with you just
in case or even in a shopping trolley.

It could be much more fun, too.

Why not get Hennessy or someone to sponsor your climb?

It should be an interesting experiment.

The more interesting experiment would be to find the pressure
necissary to push the cork INTO the bottle by increasing the ambient
pressure!

For your problem - 
At sea level you should be around 101 kPa, while at around 18000 ft
the pressure should be roughly 50 kPa (roughly).  That is only half
the pressure.  With the 'thing' as probonoblico-ga pointed out, there
should be no problem.  If your really worried you can put an
additional 'thing' on the bottle.  Eg just wrap a second wire over the
top.  But this would no doublt be over kill.

Good Luck

I'd be willing to wager that a hard vacuum would not result in the
cork spontaneously popping.  Since a hard vacuum can only result in an
increased differential of ~15psi over sea level, your real concern
should be the increased pressure from the jarring input to the bottle
from all the climbing.

Still, since you have several factors in your favor, I think you will
be fine.  First, the increase in pressure comes from the evolution of
CO2 from the champagne, the cold will work in your favor as the
solubility of gas in a liquid increases with lowered temperature
(think warm soda vs. cold).  Second, those bottles are designed for
the rigors of shipping.  Hence the thickness of Champagne bottles vs
wine, and most especially the shape of the bottom.

One important thing to keep in mind.  Glass under stress is likely to
crack with an impact.  So, I'd wrap the bottle in a closed cell foam -
like a sleeping bag pad or neoprene and then cover with some
relatively stiff sleeve material.  The idea being to minimize the
impact stresses along the lines of kneepads, etc.

Have fun and be safe.  I'd also definitely bring a full bottle, or if
you are truly insane a Magnum.  :)

Chris --

It may be difficult to answer this question with precision, but I
think that you're safe at 5600m as long as the bottle doesn't heat up
too much.  You actually have a different problem to worry about --
your champagne may foam up upon opening.  See this note in a rather
long article from Avweb, a major online aviation news source:
"A bottle of soda opened in an unpressurized aircraft at 10,000 feet
will foam and overflow."
Avweb
"When Humans Fly High" (Nov. 9, 1999)
http://www.avweb.com/news/aeromed/181893-1.html

Pilots flying unpressurized aircraft are sometime surprised when the
potato chip bag or cookie bag pops -- usually in the range of 10,000'
to 15,000'.  Those are far flimsier containers, though admittedly
there's a lot of potential energy in the carbonation in the bubbly.

Google search strategy:
unpressurized aircraft champagne bottle

Best regards,

Omnivorous-GA