As The Flavor Bible describes it, taste is “what is perceived by the taste buds.”  In common use, “taste” also includes what is we perceive through our noses while eating, but we’ll start by just addressing taste in the mouth.  In the mouth, most taste buds are on the tongue (though taste buds have also been found throughout the mouth).  Taste buds are visible to the naked eye by using a mirror and sticking out your tongue.  (They’re the little bumps.)

This is a diagram of the inside of a taste bud:

From Wikipedia Images

While food is in your mouth, it is broken down by chewing and saliva.  Some molecules find their way into the taste pore (labeled on the top of image).  Once inside the pore, the molecules may be “detected” by one of the taste receptor cells (cells in center of image).  The receptor cells contains receptors which are known to detect 5 basic tastes: sweet, salty, sour, bitter, and umami (savory).  Each receptor cell only contains receptors for one basic taste but one taste bud may contain all five kinds of receptor cells.  Though some areas of the tongue are more sensitive to one basic taste than another, the common textbook image of a “tongue map” is false – sweet is not just on the tip of the tongue, sour is not just on the side, etc.

Once a receptor cell detects enough of a basic taste, it sends a signal which travels through the afferent nerve (bottom of the image) to the brain. The signals tell the brain about the food we’ve ingested.  Sour helps us detect unripe and spoiled fruit, avoid tissue damage from acids, and maintain a balance between acids and bases.  Knowing how salty food is helps us to maintain our water and ion levels.    Umami indicates protein and peptides (like proteins but short).  Sweet indicates carbohydrates.  Bitter helps us identify toxic foods.  The reaction to these basic tastes is hard wired – infants during their first feeding smile at sweet and grimace at bitter.

Next: Each of the 5 basic tastes.

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