The findings, published in PLoS One, examined the role that bubbles play in ‘carbonation bite’ in two experiments. Together, these studies reveal that carbon dioxide bubbles are not directly responsible for the bite of carbonation – which is caused by enzymes in the mouth that convert free carbon dioxide into carbonic acid.
Carbonic acid then stimulates sensory nerve endings, which signal the mild irritation that is often referred to as the bite, said the researchers from the Monell Chemical Senses Center, USA.
However, by stimulating the sense of touch inside the mouth, bubbles do enhance this bite sensation beyond the chemical irritation caused by carbonic acid, they explained.
“Although many people naively assume that the bite of carbonation is due to tactile stimulation of the oral cavity by bubbles, it has become increasingly clear that carbonation bite comes mainly from formation of carbonic acid in the oral mucosa,” wrote the Monell experts.
The research was backed by funding from both Monell’s institutional funds and from drinks giant AB-InBev. The funders had no substantive role in study design, data collection and analysis, decision to publish, or preparation of the manuscript,
In the first experiment, the research team took advantage of the fact that bubbles cannot form when atmospheric pressure is raised above a certain level. Twelve healthy adults were comfortably seated in a hyperbaric chamber and asked to rate the bite intensity of several concentrations of carbonated water. The ratings were collected once while under normal atmospheric pressure (with bubbles) and a second time at higher pressure (no bubbles), equivalent to diving to a depth of 33 ft in sea water.
There was no difference in the bite reported in the two conditions, even though bubbles are physically unable to form at the higher pressure.
“Because the subjects experienced the same bite when bubbles weren’t present, the findings clearly told us that carbonation bite is an acidic chemical sensation rather than a purely physical, tactile one,” said study author Bruce Bryant, a sensory biologist at Monell.
Although bubbles aren’t necessary for bite, they still could be contributing to the overall sensation of carbonation, said the team. Therefore a second experiment was designed to address this possibility.
In the second experiment, 11 adults rated the intensity of bite in a laboratory setting. The ratings were made for carbonated water under normal conditions and again when additional air bubbles were added to the liquid.
The researchers were surprised to find that air bubbles enhanced the bite of the carbonated bubbles, presumably by stimulating the sense of touch.
“We thought the touch of the bubbles would suppress the painful aspects of carbonation, much as scratching a mosquito bite or rubbing a sore muscle does,” said Bryant.