Are carbonated drinks carbonic acid H?CO?

Tyler K. asks: Why does soda taste worse when it’s flat?

A notion that will come as a surprise to just about no one is that most people think soda and other carbonated drinks taste significantly better when they still contain a lot of fizz as opposed to being “flat.” It turns out that, contrary to popular belief, this phenomenon has nothing to do with bubbles popping on your tongue or the like. (In fact, when people drink carbonated beverages in a highly pressurized environment where no such bubbles can form, they report no real difference in flavor or sensation of the drink.)

So why do many fizzy drinks taste better than their flat equivalents? It’s simply because the carbonic acid (H2CO3) created via adding carbon dioxide (C02) to the drink (which obviously in turn contains H20) actually has a tangible taste that your tongue can detect and which accents the flavor of the beverage.

Thus, as these beverages are designed to taste good in their carbonated form, removing the flavor imparted by the CO2 is usually going to negatively impact taste.  Of course, this doesn’t inherently mean a worse overall flavor for any liquid that is not carbonated vs. the same drink that is. But because many carbonated beverages like popular sodas tend to have a lot of sugar or equivalent artificial sweetener, when the CO2 is removed, the extreme sweet flavor ends up standing out quite a bit more- usually more than most people enjoy. The net result of all of this is many people not enjoying the taste of “flat” sodas.

On a related note, to narrow down the mechanisms behind the taste derived from carbonating beverages, researchers in 2009 used mice that had been genetically modified to not be able to taste variously- sweet, umami, salty, bitter and sour. What they found was that those mice that could not taste sour did not react to carbonation, while all the others did.

Examining why CO2 triggers sour-tasting receptors, the researchers hypothesized (correctly, as it turns out) that a special enzyme on the surface of sour-tasting cells, carbonic anhydrase 4 (Car4), might be the culprit. Once again experimenting on modified mice, this time removing only the Car4, but not the entire sour-tasting cell, they found that “gustatory responses to CO2 were severely reduced,” but “responses to other taste stimuli, including sour, were unaltered.”

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Bonus Facts

  • While manufacturers put the same amount of CO2 in cans as bottles of soda, when placed in plastic, which is more permeable to CO2, the carbonation will dissipate relatively quickly over time. In fact, if stored in direct sunlight, in 3 months, soda in plastic can lose up to 15% of its carbonation. Cans of soda, on the other hand, can have their taste affected by bits of metal that are dissolved from the inner lining, and again, the warmer the container, the greater the effect. This is one of the reasons many people have preferences when drinking soda from glass vs. plastic vs. metal containers.
  • Four of the five tastes were known to the ancient Greeks, with Democritus (460-370 BCE), who together with his teacher Leucippus had formulated the first atomic theory of the universe, adding bitter to sweet, salty and sour. Applying his ideas on atoms to the tastes (he thought different atoms had different shapes and solidity), Democritus opined that for sweet things, their atoms were large and round, salty flavors had an isosceles triangle shaped atoms, sour flavors were also large, but rough and angular and bitter tastes had smooth, small and spherical atoms.
  • The famous chef Auguste Escoffier (1846-1935) introduced the idea of a fifth taste to European pallets with his invention of a rich, delicious, never-before seen veal stock that simply seemed to deepen and improve the flavor of everything. At the time, however, scientists refused to acknowledge that the stock embodied a taste separate from sour, sweet, salty and bitter. Kikunae Ikeda (1864-1936), a chemist, actually isolated the source of the “deliciousness” flavor of some foods (including Escoffier’s veal stock) that seemed to defy the other categories – glutamic acid, which he named umami.
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