Taste buds on the tongue have receptors that tell us if a food is sweet or sour or some other taste.

WSJ: People Who Taste Too Much

Their research was complicated by the fact that of the five primary taste sensations salty, sweet, sour, bitter, and umami the taste of salt is the least understood.

NEWYORKER: Snacks for a Fat Planet

Ketchup ignites the palate as one of the few foods to stimulate all five sensations inside the mouth: salty, sweet, sour, bitter and umami, the latter of which gives body to food and is the savory taste found in cured meat and MSG.

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