Salt does more than add a salty taste.
In the right amount, it can change how several other flavors are perceived at the same time.
That is why a small pinch can make food taste more complete without making the dish obviously salty.
Sodium activates salty taste receptors
Table salt contains sodium.
When salt dissolves in saliva, sodium ions can interact with taste receptors on your tongue.
That creates the sensation we describe as salty.
But the effect does not stop there.
Salt can reduce some bitterness
At certain concentrations, salt can make some bitter flavors less noticeable.
That matters because bitterness can mask other parts of a food’s flavor.
Reduce the bitterness a little and sweetness, savory flavors, and aromas may become easier to notice.
Salt can make other flavors seem stronger
The food did not suddenly gain new ingredients.
Your perception changed.
A tomato may taste more tomato-like.
Soup may taste richer.
Sweet foods can sometimes taste sweeter.
This is one reason salt appears in desserts as well as savory dishes.
It is also a useful reminder that taste is not produced by one receptor working alone. The same sensory system that interprets salt also has to make sense of signals such as the heat sensation explained in why chili peppers feel hot and the cooling sensation from why mint feels cold.
Why would humans care about salty foods?
Sodium is necessary for normal body function.
It helps with nerve signaling, muscle function, and fluid balance.
Humans therefore have biological reasons to detect sodium in food.
That does not mean more is always better.
Why can too much salt ruin a dish?
Once the salt level becomes high enough, salty taste dominates.
Instead of revealing other flavors, it starts covering them.
That is why seasoning has a useful range.
Too little and the food may taste flat.
Too much and the salt becomes the entire conversation.
Is salt only about taste?
No.
Salt can also affect food chemistry, preservation, texture, and cooking.
For this question, though, the important point is perception.
Salt can make other flavors easier to notice while contributing its own salty taste.
So salt does not simply make food taste salty.
Used well, it helps several other flavors get heard.
And that’s the short explanation.
Related explanations: Why do chili peppers feel hot?, Why does mint feel cold?, and Why does sugar dissolve in water?