Carbonated water is water infused with carbon dioxide gas (\(\text{CO}_2\)) under pressure. This process forces gas molecules into the liquid, creating the pleasant effervescence. Subjecting this pressurized liquid to heat causes a fundamental change in the water’s physical state. Understanding how heat interacts with the dissolved gas explains the physical changes that occur when boiling begins.
The Immediate Outcome of Boiling Carbonated Water
It is safe and possible to boil carbonated water, but the resulting liquid quickly becomes flat. When heated, a sudden increase in bubbling is observed well before the water reaches its standard boiling point of 212°F (100°C). This vigorous bubbling is the rapid escape of the dissolved carbon dioxide gas, not the water boiling.
As the temperature climbs, the \(\text{CO}_2\) molecules lose their ability to remain dissolved, forcing them out of the solution instantly. This out-gassing causes the liquid to appear to “boil” prematurely and with greater intensity than still water. Once the dissolved gas has been expelled, the liquid reverts to ordinary, flat water, which then proceeds to boil normally as it approaches 100°C.
The Science of Solubility and Degassing
The rapid loss of fizz when heating carbonated water is due to the inverse relationship between temperature and gas solubility in a liquid. Carbon dioxide dissolves easily in cold water because the low temperature allows the gas molecules to remain trapped within the water’s molecular structure.
As thermal energy is introduced, the water molecules move faster and vibrate more intensely. This increased molecular motion disrupts the weak bonds holding the \(\text{CO}_2\) in solution. The dissolved gas molecules are forced out of the liquid phase, a process known as degassing.
The amount of \(\text{CO}_2\) that can be held in the water decreases as the temperature rises. Its capacity to dissolve the gas is significantly reduced when hot, which is why carbonation is lost long before the true boiling point is reached. This principle explains why a warm soda goes flat much faster than a cold one.
Effects on Flavor and Culinary Use
Once carbonated water has been boiled, its taste is equivalent to regular flat water. The slight acidity, characteristic of carbonated water due to the formation of carbonic acid (\(\text{H}_2\text{CO}_3\)), is eliminated when the \(\text{CO}_2\) is driven off. Any mineral content, such as sodium or potassium salts, will remain, potentially concentrating slightly as water evaporates.
The resulting flat water is fine for all culinary applications, including making coffee, tea, or soup. The loss of carbonation means the water will not affect the texture of foods or beverages after boiling. While sparkling water is sometimes used unboiled in batters for a lighter texture, the boiled product offers no such advantage and is used as a substitute for tap water.