system
Given the following post, respond as if you're commenting on Reddit:
human
Does water aeration affect beverage flavor, and if so, how?

I've seen people say over and over that you need to brew coffee and tea with freshly boiled water, rather than water that has been kept warm for a long period of time or boiled multiple times.  The reason given is that the water is no longer aerated anymore.  People say the water tastes "stale", or that it makes tea taste "flat".  When asked, no one can really describe what this "flat" taste is.  Is there any sort of scientific basis to this?

I guess I can buy that extended heating or repeated boiling can drive out dissolved gasses.  If that is the case, how quickly does it happen?  Seconds?  Minutes?  Hours?  How would this affect the flavor of a beverage?  If at all, which gasses are causing the effect?  Oxygen, nitrogen, carbon dioxide, something else entirely, or a combination of several?
gpt
I believe the gas that actually affects the taste most is carbon dioxide, though it is typically stated to be oxygen. The carbon dioxide, when dissolved in water, forms carbonic acid, which has a characteristic sharp taste. It is dissolved carbon dioxide/carbonic acid, for example, which is responsible for the taste of unflavored seltzer water. Obviously, there is much less dissolved carbon dioxide in water than carbonated beverages. However, prolonged boiling will drive out the carbon dioxide, reducing the pleasant sharp taste and making the water and resulting brewed beverage taste flat. The pH increase caused by the reduced carbonic acid levels could also affect the extraction of compounds from the coffee/tea, although this effect is much more complicated.