If it's been a while since you sat in science class, here's a quick refresher: Looking at your tongue, you'll see the surface is covered with several hundred rough-looking bumps, called papillae. Each papilla contains taste buds. Some papillae have a few buds; others have a few hundred. Thus, the buds are scattered unevenly across the tongue. A smaller number lie along the throat and roof of the mouth as well [source: Monell].
Taste buds are the interface between the tongue and the brain. They contain receptor cells, where the chemical chain reaction responsible for taste perception takes place [source: National Library of Medicine]. Just as papillae have varying numbers of taste buds, buds have varying numbers of receptor cells, from one to 700 [source: Monell]. These cells are specialists, genetically coded to provide a pathway to one taste only [source: Roth-Johnson].
The process of taste begins when a food (or any substance, for that matter) enters the mouth. There it's broken down by chewing and dissolved in saliva, bathing the taste buds with its constituent chemicals. Through different means (more on that later), the receptor cell walls translate these chemicals into electric impulses, a process called transduction. Nerves adjacent to the cells relay these impulses to the nucleus of the solitary tract of the brain, or NST. The NST compiles them into a message that identifies the taste.
Taste is the initial factor in determining whether a substance in the mouth is OK to eat. Deciding to eat the food depends on more than taste, however. It involves flavor. Flavor is a multisensory effect. It includes not only a food's taste, but also its aroma, texture, temperature, intensity and even the memories and emotions it evokes. Processing all this information engages several higher-function areas of the brain [source: Monell].
That's the basic route by which food in your mouth becomes taste to your brain. Next, we'll look at umami's particular ways and means.