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The bubbly chemistry behind carbonated beverages

Many people love the refreshing effervescence of a soda, champagne, beer or sparkling water. When you take a sip, the gas bubbles in the beverage burst, and the tickles your nose. But have you ever wondered how carbonation actually works?

I'm a and a carbonated beverage enthusiast and home brewer myself. While the basic process of carbonation is relatively simple, a variety of factors—from temperature to surface tension—can affect the taste and quality of beverages.

Dissolving carbon dioxide

Carbonation involves dissolving the colorless and odorless carbon dioxide—CO₂—gas into a liquid. When carbon dioxide is added to a sealed bottle or can containing water, the pressure in the bottle or can increases, and the into the liquid.

The COâ‚‚ above the liquid and the COâ‚‚ dissolved in the liquid . Chemical equilibrium essentially means the rate that COâ‚‚ dissolves into the liquid is equal to the rate that COâ‚‚ is released from the liquid. It's based on the amounts of COâ‚‚ both in the air and in the liquid.

Some of the dissolved CO₂ reacts with the water to form carbonic acid, which has a chemical formula of H₂CO₃. So once some of the dissolved CO₂ converts to H₂CO₃, more CO₂ from the air above can dissolve into the liquid and reestablish chemical equilibrium.

When you open a bottle or can, the pressure above the carbonated liquid drops to match the pressure outside of the bottle or can. The pressure release results in a hissing sound, and you see bubbles rising in the liquid as the H₂CO₃ converts back to CO₂ and that gas . The carbonic acid in the beverage is what makes it .

A colder drink is a bubblier one

Another important factor influencing carbonation is temperature. Most gases, including carbon dioxide, do not dissolve well in liquids as the . That's why if you leave them out at room temperature.

Conversely, if you place your favorite carbonated beverage in the refrigerator and allow it to get cold, more dissolved carbon dioxide will stay in the beverage while it's still sealed. When you open the chilled bottle or can, the because there was more dissolved carbon dioxide in the cold beverage.

Surface tension and fizziness

One final important factor for carbonation is the surface tension of the liquid. A liquid's surface tension is determined by how strongly the liquid's . For most beverages, those molecules are water molecules, but diet soft drinks have artificial sweeteners dissolved in them. These sweeteners can weaken the interactions between the water molecules, creating a lower surface tension. A lower surface tension means the carbon dioxide bubbles .

This is why it takes slightly longer to be served a Diet Coke on ice, a problem you might notice on a plane. The lower surface tension from the artificial sweetener means there's more fizz, and for longer, compared with other soft drinks. The flight attendants then have to before they can fill the cup with more Diet Coke.

Surface tension is also why Diet Coke works so well in the , during which you drop Mentos candies into 2-liter Diet Coke bottles. The candy helps to weaken the interactions between the water molecules and the COâ‚‚ molecules, lowering the surface tension and allowing for an easier release of COâ‚‚ molecules. A bubbling "geyser" of Diet Coke rises fast above the 2-liter bottle as the COâ‚‚ molecules quickly form on the candy's surfaces and force the Diet Coke out of the bottle.

Getting the bubbles into a beverage

In an effort to make water similar to that from mineral springs, the carbonation process was invented by Joseph Priestley in England in the 1760s and commercialized by Jacob Schweppe—recognize the name?—. Priestley reacted chalk with sulfuric acid, producing CO₂, and he hung a water-filled container over the reaction to .

Today, most commercial beers, soft drinks, seltzers and sparkling waters are created by "forced" carbonation. This is when manufacturers directly inject carbon dioxide into the beverage .

A second common way to introduce carbon dioxide into a liquid is by . Champagne manufacturers and some small follow this method by sealing a sugar source and live yeast into their bottles. The yeast produce alcohol and carbon dioxide, and this carbon dioxide increases the pressure in the bottle, resulting in . But this process is not as controlled and can result in .

Larger brewers often capture COâ‚‚ produced during a fermentation process and pump that gas into the tanks that contain beer to carbonate the beer. This is normally a controlled process that allows for to be introduced into the beverages for outstanding consistency.

Carbonation is a marriage between physics and chemistry—one that transforms ordinary liquids into effervescent treats. The next time you drink a carbonated beverage, take a moment to appreciate the science behind those dancing bubbles.