NASA has gone to great lengths to recreate space-friendly versions of familiar foods for astronauts, but there are certain delicacies enjoyed on Earth that just don’t make the jump to micro-gravity very smoothly.
Among those best-enjoyed-at-home treats is cola. Carbonated cola in the form of Pepsi and Coca-Cola were first flown into space aboard shuttle mission STS-51-F in 1985, but the astronauts excitement over having such a classic treat on the menu was short lived. On Earth, gravity separates the solids and liquids in our stomach from the gases. In micro-gravity, there is no such mechanism at work to keep the food at the bottom of your stomach and allow the gas to rise to the top. The same issue affects the can itself, too. Crack open a cold one here on Earth and the gas immediately rises to the top (and the carbonated liquid eventually goes flat). In the micro-gravity of Earth orbit, the gas stays suspended in the solution longer and every sip is significantly more carbonated than it would be on Earth.
Between having to drink the cola from a specially adapted container (the photo here shows the approach Pepsi and Coca-Cola took to the problem), each swig being hyper-carbonated, and the very unsettling feeling you get when a big dose of carbonation is sending your stomach contents bouncing around—on top of the fact that it’s difficult to burp because the gas won’t come out of suspension and rise to the top of your stomach—you can imagine why cola in space just never caught on. There’s just no cola delicious enough to put up with the mess and hours of gas pains.
Though NASA and other space agencies have experimented with various carbonation delivery systems and formulas, carbonated drinks remain, understandably, unpopular among astronauts, and since the experiments in the 1980s, have been largely absent from space flights.