The complex, nuanced experience we perceive as “taste” is actually a sophisticated sensory combination known as flavor. Many people describe a rich aroma as something they can “taste,” and scientifically, this observation holds a profound truth. Flavor involves a dynamic partnership between the tongue and the nose that is far more intricate than simple taste buds working alone. This combined perception is what allows us to savor a complex meal or a perfectly aged cheese.
The Separate Roles of Taste and Smell
The sense of taste, or gustation, is limited to the tongue and a small area of the mouth and throat. Taste receptors on the tongue are specialized to detect only five basic categories: sweet, sour, salty, bitter, and umami (savory). These receptors are chemosensors that can only interact with non-volatile chemical compounds that are dissolved in saliva.
The sense of smell, or olfaction, is chemically distinct and far more complex than taste. Olfactory receptors, located high in the nasal cavity, are responsible for detecting volatile molecules—those that easily evaporate into the air. Humans possess hundreds of olfactory receptor subtypes, which work in various combinations to allow the perception of thousands of distinct odors. These two sensory systems function as separate biological pathways, with one dealing with dissolved chemicals and the other with airborne molecules.
The Creation of Flavor: Retronasal Olfaction
The richness we associate with a food’s identity, such as distinguishing a lemon from a lime or coffee from chocolate, is the result of flavor. Flavor integrates the tongue’s basic taste signals with the nose’s highly detailed smell signals, along with other inputs like temperature and texture. The mechanism that unites these two senses during eating is called retronasal olfaction.
When food is chewed and swallowed, the process releases volatile aromatic molecules from the food. Instead of exiting the mouth, these molecules travel backward up the throat and through an internal passage called the nasopharynx. This pathway directs the airborne molecules up to the olfactory receptors in the nasal cavity from the inside.
The brain receives these internal scent signals simultaneously with the basic sweet or sour signals coming from the tongue. The brain interprets this combined input as a single, unified experience—the complex flavor of the food. Retronasal olfaction is specifically what allows for the discrimination of subtle flavor dimensions beyond the five basic tastes. This internal route is so effective that the brain often misattributes the smell sensation to the mouth, leading to the common belief that we “taste” the aroma.
Why Food Tastes Bland When You Are Sick
The role of retronasal olfaction is demonstrated when a person has a common cold or the flu. When the nasal passages become congested, the inflammation and mucus physically block the internal retronasal pathway. This blockage prevents the volatile aroma molecules from traveling up the nasopharynx to reach the olfactory receptors.
Because the odor signals cannot reach the brain, the only sensory information left is the simple input from the taste buds on the tongue. A person can still perceive if a food is sweet, salty, or bitter, but they cannot register the details that make an apple distinct from a potato. This disruption in the combined sensory process leads directly to the sensation of food being dull, flat, or flavorless, despite the taste buds themselves functioning normally. A more permanent loss of smell, known as anosmia, similarly eliminates the complex flavor experience by permanently shutting down this pathway.