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Taste is the orphaned sense. Even among those interested in the field, it plays sidekick to smell. “Taste is a waste, the action’s in olfaction” goes the quip. Few researchers study it, and when they do it is usually for the food industry. But such efforts are built on very little basic science. The bodily processes behind taste—how information begins in the taste buds and then is sent via nerves to the brain, to be merged with input from the eyes and the nose and formed into a conceptual whole—remain unclear. “With taste, believe it or not, we’re still not actually sure how salty works,” Marcia Pelchat, a researcher on food at the Monell Chemical Senses Center, in Philadelphia, says. “That just amazes me.”
It is only in the past decade that the redoubtable “map of the tongue” has begun to fall out of circulation. The diagram, which dates to the early twentieth century and can still be found in some medical textbooks, places the taste buds for sweetness on the tip of the tongue, those for bitterness at the back, the ability to sense salt on the top edges, and sourness on the bottom edges. When [chef Grant] Achatz showed me what had happened to his taste buds, he explained it by making reference to the classic map, as did his surgeon. In fact, all the regions of the tongue are capable of recognizing sweet, salty, bitter, and sour flavors, as well as savory tastes, which had been left off the original map altogether. There is now speculation that there are receptors on the tongue’s surface for other kinds of tastes. “There may be one for the metallic taste, the water taste, and the fat taste, and there may be other tastes as well,” Leslie Stein, another researcher at Monell, told me.
But, however many kinds of tastes we can apprehend, they will never truly account for what we experience as flavor. The taste buds cannot detect nutty, buttery, or earthy tastes. They do not know beef from lamb. Researchers think that the role of taste in our evolutionary past may explain why it is such a blunt instrument. Our ancestors were hominids who spent much of their time in trees, as chimpanzees do. Their taste for sweet foods helped them find nutritious fruits, and their ability to sense bitter tastes helped them to avoid poisonous plants. But to find edible fruits and avoid toxic ones you don’t need very subtle information: cover the bitterness of cyanide with sugar, and a person will happily drink it. Taste is an easily outwitted sense.
-- D. T. Max, “A Man of Taste,” The New Yorker
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