I'm in the mountains and had a poor experience when I tried to drink a soda. I poured it at room temperature over ice and it fizzed up more than usual. When I tasted it, I found the soda was nearly flat; but why was it flat? What factors led to the soda losing all that precious carbonation?
The bubbles in soda that tickle your tongue are caused by carbon dioxide. That's right, that devil of a greenhouse gas makes your soda delicious. Carbonation gives drinks their fizz by dissolving CO2 in the soda, which is kept in the can under pressure. That pressure forces the CO2 to stay into the liquid, but when we open a can the increased pressure quickly escapes, CO2 is forced out and comes together to create bubbles.
When we drink it the CO2 interacts with the water in the can and on our tongues creating carbonic acid. This gives a pleasant and familiar sour taste to counteract the sweetness of the soda. This means the CO2 is very important in the taste and mouthfeel of the soda, and without it we're left with an overly sweet, flat flavor.
The first mistake I made was drinking room temperature soda. The soda's ability to dissolve CO2 actually decreases as temperature increases. This is the general rule of all gases and is different than most solids like sugar. The solubility of sugar in water drastically increases with temperature. But having a warm soda meant not much CO2 could be dissolved and when opened let the gas escape. This is a relatively small effect and independent of altitude.
The second issue is that I'm trying to drink soda in the mountains, fairly high in the mountains too. As we increase in altitude atmospheric pressure decreases. Compared to sea level atmospheric pressure up here is about a third less. Decreased pressure has the largest impact on my soda. Who's ability to dissolve CO2 increases with pressure, like it's being forced into the liquid. But in the mountains a lot of the pressure is gone and when we open the can and pour the soda CO2 comes out in bubbles and the soda becomes flat, especially if it was room temperature which just exacerbates the problem.
Unfortunately, there's not really an easy way around this. I could try and makeup for the lack of carbonic acid by adding some acid to the soda. Or go really extreme and build a pressurized soda drinking room. But other than that, there aren't many options but getting used to the flat mountain soda.
UPDATE: Things have gotten more complicated. Mainly in the fact that there is advice to improve things. While spending more time in the mountains I discovered that soda in a glass of ice water was destined for failure. However if you keep the soda in the can, even with the reduced atmospheric pressure things actually turn out alright. If I had to guess I'd say it's just not that easy for the gas to come together and escape. That is unless you pour it out into open air over a bunch of ice cubes, spreading it out and letting it lose all that beautiful CO2. What I'm saying is keep it in the can.