What, you say the secret of good soda is not bubbles?
What, you say the secret of good soda is not bubbles?
This soda is actually very sour

(this article starts in the fruit shell)

it feels so good to open a bottle of chilled soda and gulp it down. In addition to the sweet flavor, soda drinks in the mouth will also produce a "tongue piercing" irritation, which is the unique charm of carbonated drinks. Have you ever wondered where this feeling came from?

well, maybe not. The answer seems too obvious: isn't it the touch of small bubbles in soda that come into contact with the mouth?

however, this is not the case.

the taste of soda doesn't come from bubbles.

in 2013, an experiment proved that bubbles are not a necessary condition for tasting carbonated drinks [1]. In other words, as long as there is enough dissolved carbon dioxide, even if a carbonated drink is not bubbling, you can still taste the excitement from it.

(the bubbles we see are not really the key to the taste of carbonated drinks | stevepb/pixabay)

how does this prove? The researchers moved the carbonated water test into a hyperbaric chamber. Here, the ambient pressure rises to twice the atmospheric pressure (which is equivalent to diving 10 meters in the water, which is tolerable), so that the carbon dioxide in the sample can remain dissolved and does not become bubbles to escape, resulting in a cup of "bubble-free soda".

the researchers asked subjects to taste several carbonated water samples with different carbon dioxide contents in atmospheric pressure and pressurized environment, and rated their irritation. Of course, in order to remove the influence of other variables, these samples are not fat happy water, but just pure water filled with carbon dioxide. As a result, when carbon dioxide bubbles were not produced under high pressure, the tasters still rated the irritation of carbonated water as much as under normal pressure, and the irritation score increased with the increase of carbon dioxide content.

(in the experiment, people evaluate the irritation of carbonated water on the tongue as S.M. Kappes et al)

bubbles are not the main cause of irritation, but their existence does have some effect on the taste. In another experiment in the same paper, the researchers added extra air bubbles to low-concentration carbonated water, which was "not enough", and asked the subjects to conduct another round of evaluation. The results show that adding bubbles does increase the irritation of carbonated water, but if you just add air bubbles to white water, it still won't produce a soda-like taste.

interestingly, in this experiment, when the researchers asked subjects to rate only the "touch from bubbles", they still gave fairly high marks to the samples under high pressure-but both theoretical and practical observations showed that there were no bubbles in the carbonated water at all. Thus it can be seen that the concept of "thrill = bubble" is really deep-rooted.

in fact, what you taste is acid

if it's not the touch of bubbles, what's the stimulation of soda? Many studies have confirmed that this unique feeling of carbon dioxide solution in the mouth actually comes from acid-that is, carbonic acid. This should include both the sour taste felt by the taste receptor and the irritation of the "nociceptor" activated by the acid.

and so on, can carbonic acid really be so exciting? In theory, the ability of carbonic acid to ionize hydrogen ions is weak, but there is another factor on the tongue that makes it "more acidic"-carbonic anhydrase on the surface of the cell.

(carbon dioxide dissolved in water itself is not very acidic. The pH value of this bubble water in the picture is 4.96 [2]. But our tongues can make it "sour".

carbonic anhydrase can catalyze the reaction of carbon dioxide with water to form bicarbonate and hydrogen ions. This reaction can occur without catalysis, but the presence of an enzyme makes it much more efficient. In this way, more hydrogen ions can be produced locally, resulting in a stronger sense of acid.

some experiments have shown that carbonic anhydrase is indeed the key to perceiving carbonic acid stimulation. If a drug solution that inhibits carbonic anhydrase (the drug is called acetazolamide, which can be used to treat glaucoma) is applied to the subjects' tongues, their evaluation of the irritation of carbonated water is significantly weakened. the perception of other sour tastes such as citric acid did not change [3].

there is another interesting thing. Experiments also show that the tongue can feel gaseous carbon dioxide (not in the air, the concentration is too low). It should be carbonic acid when it encounters water in the mouth.

how to drink more exciting?

if you want to fully feel the irritating taste of carbonic acid, of course, the most important thing is "Qi should be sufficient"-the higher the concentration of carbon dioxide, the stronger the irritation of sticking the tongue. However, other factors also affect how people feel about soda.

for example, just like life experience, the study also found that cool carbonated drinks tasted more irritating than those close to body temperature, while menthol, which creates the illusion of coolness, did not enhance it [4]. In addition, capsaicin slightly reduces the irritation of carbonic acid [3].

sight and hearing also affect how people feel about drinks. In one experiment, the researchers recorded the sound of soda bubbling with a microphone and asked subjects to listen to these "soda ASMR" for comments. The results show that if you turn up the volume of soda or increase the high-frequency part, you can make you feel "more breathing" [5].

(it is said that listening to the sound of bubbles can increase the soda tasting experience | Massimiliano Zampini, Charles(Spence)

the next time you drink soda, listen to it.






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