The bitter-reducing ability of salt is a marvel. It is why coffee aficionados add an undetectable pinch to their grounds before brewing, says Barry Smith of London University’s Centre for the Study of the Senses…. But it is not easy to uncover the precise mechanics of this culinary godsend, what with it occurring on a molecular level. We do know that it is a physiological phenomenon, rather than cognitive. Even if there isn’t enough salt in our mouths for us to consciously taste it, the effect will still happen. And if you stimulate one side of the tongue with salt, and then put something bitter such as quinine on the other side, the salt will generally not suppress the bitterness. The two tastes have to be hitting the same receptors for it to work. Put very simply, we think that sodium ions turn down bitter responses in the receptors.
For more, including two distinct ways that salting can influence aroma, head here.