One of the items the astronauts might like to have when they are on orbit is soda, or carbonated beverages. Many years back, they decided to fly the soft drink Coca Cola® on the shuttle. First, it had to be packaged in a special can to keep it under pressure so it wouldn’t lose its carbonation, and to keep it under pressure so the soda and the carbonation would not separate in microgravity. Not only is carbonation difficult in microgravity, it causes you to burp. On earth, that’s not such a big deal, but in microgravity it’s just gross! Because there is no gravity, the contents of your stomach float and tend to stay at the top of your stomach, under the rib cage and close to the valve at the top of your stomach. Because this valve isn’t a complete closure (just a muscle that works with gravity), if you burp, it becomes a wet burp from the contents in your stomach.
Source: NASA Quest > Space Team Online (dead link – http://quest.arc.nasa.gov/people/journals/space/kloeris/05-01-01.html)