The experience of drinking a carbonated beverage often includes a familiar sensation that is sharp, tingling, or sometimes slightly painful. This feeling, commonly called “fizz” or “burn,” is not a true taste like sweet or sour, but rather a somatosensory perception. It is a direct response from your body’s sensory system reacting to the chemical and physical properties of the drink. This feeling is an example of how carbonation creates a complex physiological response in the mouth.
The Role of Carbonation
The foundation of a fizzy drink lies in the physical process of carbonation, which involves dissolving carbon dioxide (CO2) gas into a liquid. Manufacturers force large amounts of this gas into water under high pressure, a process governed by Henry’s Law. This law states that the amount of gas dissolved is directly proportional to the pressure above the liquid. To maximize dissolved gas, the liquid is also kept cold, since gases are less soluble in warmer temperatures.
The high pressure inside a sealed container keeps the CO2 molecules trapped in the liquid. When the container is opened, the “hiss” sound signals the immediate release of this pressure. With the external pressure lowered, the liquid can no longer hold the same volume of gas. This shift causes the dissolved CO2 to rapidly escape, forming the streams of bubbles that rise to the surface, which is the visible sign of the drink going flat.
The Creation of Carbonic Acid
While the bubbles contribute a physical tickle, the actual “burn” is rooted in a subsequent chemical reaction. Once carbon dioxide (CO2) is dissolved in water (H2O), a small fraction of the gas molecules react to form carbonic acid (H2CO3).
Carbonic acid is a weak acid, but its presence significantly alters the liquid’s acidity. Carbonated water typically has a pH between 5 and 6.5, a localized drop that acts as the chemical trigger for sensory receptors. The formation of carbonic acid and its dissociation into hydrogen ions (H+) ultimately leads to the sensation of irritation in the mouth.
How Your Mouth Registers the Sensation
The brain registers the soda burn not through the taste system, but through the somatosensory system, specifically involving the trigeminal nerve. This fifth cranial nerve transmits touch, temperature, and pain sensations from the face and the oral cavity. It is the same nerve that registers the pungency of chili peppers or the cooling sensation of menthol.
When the carbonated beverage is consumed, the dissolved CO2 gas quickly passes through the membranes of the sensory nerve endings. Inside the nerve cells, the CO2 is converted to carbonic acid at an accelerated rate by specialized enzymes called carbonic anhydrases. This rapid conversion causes a sharp increase in the concentration of hydrogen ions inside the nerve cell, leading to intracellular acidification.
The change in acidity within the nerve cell activates a specific sensory receptor known as the Transient Receptor Potential Ankyrin 1 (TRPA1) ion channel. TRPA1 channels are nociceptors, responsible for detecting irritating stimuli. The activation of these channels sends a neural signal to the brain that is interpreted as a stinging or burning feeling, separating the experience of carbonation from the tongue’s basic taste receptors.