Salt makes the sweet and sour flavors of a margarita pop. Even a little bit of salt suppresses bitterness, which in turn makes sweetness and sourness seem more intense. However, calling salt a flavor enhancer can be misleading – no clear physiological connection between salt and universal flavor enhancement has been found.
What we do know is that salt seems to boost certain basic tastes by suppressing others. Adding even a pinch of salt to a mixture tamps down its bitterness. Since that bitterness would otherwise be counteracting the drink's sweetness, adding salt enhances the perception of sweet flavors.
For the beloved margarita, adding a small amount of salt screens out the slight bitterness of the orange liqueur (Cointreau or triple sec). At the same time, it also heightens the taste of the lime juice and softens the tequila’s bite.
$3 Margaritas (with or without) salt are the special today.