I've seen this phenomenon a couple of times--I actually saw it happen this night.

When a carbonated beverage is poured into a cup or glass, many tiny bubbles of carbon dioxide form on the bottom of the glass, then shoot up to the surface and pop when they get too big.

Today, as I was looking at a wine glass filled with a carbonated beverage, I noticed that there was something different--the carbon dioxide bubbles were rising up in a straight column from the very center of the cup; in other words, all the CO2 bubbles were coming from the point where the cup joined the stem.

Can someone explain how this phenomenon happens?