Carbonation Science Questions Answered

Enlarge Image Image Gallery When released to the atmosphere, carbonation can tickle the nose and please the palate. iStockphoto.com/Vladimir Vladimirov

When I was little, my mom went through what she calls her “Earth Mother” phase (it was the ’70s). At one point, she decided to make her own root beer. She sent away for a book with the recipe and some bottle caps. We followed the recipe, had a great time using my great-grandfather’s bottle capper, and put the bottles in a cool corner of the basement to finish. Some time later, my brother and I went down to the basement to play and found sticky root beer on the walls and ceiling. The bottles hadn’t exploded (we had those heavy-duty, glass pop bottles back then; the ones that you drank in the store so you got your nickel back), but the cap had blown off one of them. After that, I remember taking the bottles outside, carefully – “Point the bottles away from your face. … No, Jenny, don’t point it toward your brother” – and dumping the contents, which smelled pretty strongly of bread dough. What went wrong, and how does carbonation science work?

It was all about our carbonation methods. We Americans love our fizzy drinks – soda pop, beer, champagne. Studies show that carbonation has a “taste.” It activates the portions of our tongues that taste sour things (which is why flat drinks taste, well, flat).

Carbonation is created when carbon dioxide (CO2) dissolves in liquid. The amount of CO2 that will dissolve is dependent on temperature and pressure. CO2 will dissolve in a liquid until “equilibrium” is reached – when the amount of carbon dioxide in the liquid and the amount in the air above the liquid are the same. In a sealed container, an excess of the gas can be dissolved if it is used to pressurize the airspace above the liquid. When you open a carbonated drink to the outside air, the pressure is released, and the CO2 leaves the liquid to reestablish equilibrium. If you recap the bottle, enough escapes to return to equilibrium, leaving the liquid just a little bit flatter. If you leave it open to the air, most of the CO2 will leave the liquid, and the drink will go completely flat.