When food is consumed, the resulting complex sensation is often called “taste,” but this term only captures a small part of the experience. Taste, or gustation, is limited to the five basic sensations detected by receptors on the tongue: sweet, sour, salty, bitter, and umami. Flavor, however, is a holistic sensory experience created by the brain that integrates gustation with other inputs. This perception includes the food’s texture, temperature, and, primarily, its aroma. The full profile of a meal is synthesized by the brain from a combination of different stimuli.
The Dominance of Olfaction in Flavor
The vast majority of what people perceive as the “taste” of food is actually derived from the sense of smell, or olfaction. Neuroscientific consensus places the contribution of smell to overall flavor perception between 75% and 95%. This wide range exists because the complexity of the food and individual physiological differences can shift the exact proportion. For example, a simple solution of salt water relies heavily on taste receptors, while a complex dish relies almost entirely on aroma for its specific identity.
This high percentage illustrates why the five basic tastes alone are insufficient to distinguish between most foods. Without the accompanying scent, an apple and a raw potato may only register as sweet or starchy, making them nearly indistinguishable. The human tongue possesses only a few types of taste receptors, but the olfactory system contains hundreds of different receptor types. This anatomical difference allows for the perception of thousands of distinct aromas, providing the detail that differentiates one fruit from another. When the sense of smell is removed, flavor collapses into its foundational taste components and physical feel.
The Mechanics of Retronasal Smell
The dominance of smell in flavor perception is due to a mechanism known as retronasal olfaction. Odor molecules, or volatile compounds, reach the olfactory epithelium—the tissue containing smell receptors—through two distinct pathways. The first is orthonasal olfaction, which occurs when inhaling air through the nostrils, detecting external scents before the food enters the mouth. This pathway helps anticipate flavor.
The second pathway, and the one most important for flavor, is the retronasal route. Here, aroma molecules are released from the food inside the mouth. As food is chewed and warmed, these volatile compounds travel from the oral cavity, up the back of the throat, and into the nasal cavity. The molecules stimulate the same olfactory receptors that detect external scents, but the brain processes these internal aromas and “refers” the sensation back to the mouth. This creates the illusion that the flavor originates directly on the tongue.
This anatomical loop allows a single, continuous sensory experience to be perceived as flavor. The movement of the jaw and tongue during mastication helps release a steady stream of aroma compounds into the retronasal passage. This continuous detection of volatile molecules allows the brain to construct a dynamic, evolving flavor profile as the food breaks down.
When the Flavor System Breaks Down
The dependence of flavor on aroma becomes clear when the olfactory system is temporarily compromised. A common cold or severe nasal congestion causes a temporary state of anosmia, or the inability to smell, by blocking the pathway for volatile compounds. During a cold, food often seems bland, a phenomenon not caused by a failure of the taste buds. In this state, the complex flavor of a meal is reduced to its texture, temperature, and simple sweet, sour, salty, or bitter qualities.
This sensory loss demonstrates the smell-to-flavor ratio. The capacity for olfaction also tends to decline naturally as people age, particularly after the sixth decade of life. This age-related decline often results in a perceived loss of flavor sensitivity, causing older individuals to report that food no longer tastes as vibrant. The reduced ability to detect retronasal aromas is the primary reason for this change, not a loss of basic taste function.