Gases in Liquids

The Theory

The tickling sensation in soft drinks results from carbonic acid. However, this name is misleading. In fact, the bubbles in beverages are carbon dioxide (CO₂), an oxide of carbon. Carbon dioxide is a colourless, non-flammable, non-toxic and slightly acidic-tasting gas, which is also part of the air. It is produced by lime burning. In water, only 0.2% of the carbon dioxide reacts to carbonic acid. The remaining 99.8% of the gas is simply dissolved in the water. Therefore, carbonic acid is only slightly acidic. Because of the excellent solubility of CO₂ (see picture), more than 3 litres of CO₂ can be dissolved in one litre of water.

Soda Water and Soft Drinks

With the right equipment, it is possible to turn tap water into soda water at home. Basically, a CO₂ cartridge is all that is necessary. In general, it is of great importance to refrigerate carbonated beverages, since carbon dioxide becomes less soluble when it is heated and escapes. That’s why lukewarm cola tastes so boring in the summer, as only a little carbon dioxide remains dissolved.

"Behaviour" of a Soft Drink Can

Because cans are under pressure (it is not possible to compress them!), part of the CO₂ escapes when the can is opened. The gas expands rapidly and causes a brief cooling. Water vapour condenses and sinks downwards as a fine mist, together with the heavier CO₂. The carbon dioxide molecules form small bubbles on condensation nuclei (uneven surfaces or tiny impurities on the can wall), and float to the top and escape. If the beverage was kept in the warmth, many CO₂ bubbles escape at once, as they are no longer able to dissolve in the beverage. The escaping bubbles drag liquid along with them, and this is why soft drinks, beer and sparkling wine fizz and sparkle when opened.

However, in many beverages the carbon dioxide is not added with the help of a CO₂ cartridge. In mineral water, for example, the water picks up minerals and carbonic acid in the course of its journey through the rocks. CO₂ in beer and sparkling wine is generated during and because of the process of alcoholic fermentation.

E 290 = Carbonic Acid

Carbonic acid not only improves the taste, but also lengthens shelf life. Moreover, it is used as an acidifier and refrigerant. It is referred to by the number E 290.