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Coffee served hot can be quite bitter (presumably high pH).

Several people I have known will add a single grain of salt to the coffee - which reduces the perceived bitterness.

My question is: What is the reason a grain of salt alters the perceived bitterness of coffee by such a high degree? Can you explain the pH change that is occurring during this reaction?

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  • $\begingroup$ The addition of even a moderately large amount of salt to pure water does not significantly make the solution any more alkaline or acidic. Coffee or tea aren't as simple as pure water, but I imagine the effect is about the same. I don't think bitterness has to do with the pH at all; the bitterness in coffee and tea come from dissolved alkaloids, of which caffeine is one. Alkaloids often produce basic solutions, but you can certainly make basic solutions without them. Whether such solutions are bitter, I don't know, as I haven't really felt the urge to taste $0.1\ M\ \ce{NaOH}$! $\endgroup$
    – Nicolau Saker Neto
    Commented Feb 14, 2014 at 23:45
  • $\begingroup$ That's exactly my point - why salt and not baking soda? What is the reaction that reduces the bitterness? $\endgroup$
    – hawkeye
    Commented Feb 15, 2014 at 0:36

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Is simply a dissolution no reaction occur and as said Niculau the pH change, if occur, is absolutely negligible.

Salt in general affect taste lowering the bitterness of the food enhancing the positive sensory attributes of foods. In fact the reason of this behavior is the sodium ion $Na^+$ (even litium ion works) and his interaction with the receptors in taste buds. So sodium acetate therethically works as well, Gery Beuchamp has studied many of this salt, quoting from NCBI:

various sodium-containing ingredients have been known to reduce the bitterness of certain compounds found in foods, including quinine hydrochloride, caffeine, magnesium sulfate, and potassium chloride

This is an article about the suppression of bitterness by sodium. From here I'm afraid is more a question of physiology.

I read this the first time here:

This, Herve. Molecular gastronomy: exploring the science of flavor. Columbia University Press, 2006 p. 94

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