Is Coke worse for your teeth when fizzy or flat?

Everyone knows that Coke is bad for their teeth. It’s sugary and acidic.

The acidity is at least partially caused by carbon dioxide (CO2) dissolved in the water, to make carbonic acid. We also know that if you pour a Coke and leave it, it fizzes away as the CO2 comes out of solution and returns to its gaseous state. Does this mean that Coke becomes less acidic if you pour it and leave it for ten minutes before drinking?

Well, perhaps.

It’s also worth remembering that small changes in temperature can cause large changes in the rate of chemical reactions. If we assume our can of Coke was in the fridge at perhaps 3°C, then it will warm up in the time we leave it to fizz away. So even if it’s less acidic, the weaker, warmer acid might be able to react with our teeth faster than the stronger, cooler acid.

I am not a chemist but I want to find the answer to this thought experiment.

After a little research, it seems that dissolved CO2 (carbonic acid) is only one contributor towards the overall acidity. The most significant acid is phosphoric acid. As the CO2 comes out of solution and escapes as gas, the acidity only decreases slightly. On the other hand, when the coke warms up from 3°C to maybe 10°C as it approaches room temperature, the action of the acid will be massively accelerated.

So based on this mini experiment, Coke is worse for your teeth when it goes flat and gets warm. This, of course, neglects the action of the sugar on your teeth and all the other things  we haven’t considered, so don’t blame me if you lose your teeth from drinking gallons of ice-cold Coke 😉

6 thoughts on “Is Coke worse for your teeth when fizzy or flat?

  1. Hi Jonathan,

    I found through a search that a few of your posts include links to You might not have heard that in January of this year, the owner of that domain sold it to the commercial wiki farm “Wikia,” and it now redirects to

    I don’t know if Coke is bad for your teeth, but it seems bad for a website:
    Wikia Ads 2

    Most of our editor community jumped ship, and we’ve split off a non-commercial fork at No ugly ads, and lots of new contributions. Please check out both for yourself and see. I’m happy to answer any other questions you might have too.

    Thanks and cheers,



    1. I noticed that the domain had changed. I assumed the administrators had migrated to a wiki hosted by Wikia to save on server costs, or something like that. Many other websites now host with cloud services (not me!), so it didn’t seem too surprising.

      I’ve contributed to in the past and it’s a fantastic resource. Thanks for the heads-up, I’ll be sure to make my edits on the new, non-commercial website.


  2. In my science project, What substance should I use instead of teeth. On one website I got eggshells but I want more items.
    Also what soda should I use of your science project for Flat (warm) vs. Fizzy (cold) for what temperature will decay your teeth more?


    1. If you want a substitute for teeth you could try almost any mineral. Egg shells are a good idea because they are made of the same stuff as teeth. You could also try chicken bones, antacid tablets and of course the classic trick with adding coins to make them clean.

      I’m not sure whether flat and warm soda decays teeth faster than cold and fizzy. As it’s your science project I reckon you should get a cup of warm, flat soda and a cup of cold, fizzy soda and put an antacid tablet in each. Time how long it takes each to dissolve.

      Have fun! 🙂


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