Aroma And Retronasal Smell: Two Routes Into Flavour

Two Entrances To The Same Sensory Area

When we smell the aroma rising from a cup, volatile molecules enter through the nostrils: the orthonasal route. Aroma molecules released while food is in the mouth can instead travel along the passage connecting the upper throat to the nasal cavity. This is the retronasal route.

Both routes reach the olfactory area high in the nasal cavity. They differ in the direction of arrival and in when the molecules arrive during eating. Smelling a food and perceiving its aroma from within the mouth involve molecules reaching the same sensory area through different routes.

Smell a hot sauce in its bottle, then taste it within a bite, and you can follow these two encounters. In the first, you approach its smell from outside; in the second, aroma from the food in the mouth is experienced with taste and texture. The same sauce contributes through two routes to the olfactory area.

How Do Taste And Aroma Meet In A Mouthful?

Sweet, sour, salty, bitter and umami are taste qualities. Words such as fruity or floral usually describe smell. Texture, temperature and chilli heat contribute other information to the same eating experience. In English, ‘flavour’ names the experience formed by these sensory contributions together.

Retronasal smell occurs alongside taste and texture sensations during eating; in everyday language, the whole experience is often called ‘taste’. Information arriving through the distinct taste and smell pathways can contribute to the same flavour experience.

In Khorisantono, Veldhuizen and Seubert’s 2025 study, the 25 participants included in the analysis first became familiar with congruent taste–odour pairings. Tastes and odours were then delivered separately during functional magnetic resonance imaging, or fMRI. Associated tastes and retronasal odours produced overlapping patterns in the brain’s insula, particularly its ventral anterior region. The finding provides a neural counterpart to distinct sensory inputs meeting in a shared flavour identity.

Here, a “shared pattern” was investigated by distinguishing flavour identity from the distribution of brain activity within a region. A classifier trained on taste responses could also distinguish the associated odours, revealing information shared between taste and smell. Overlap was therefore tested as a relationship between stimuli presented separately.

The Role Of Air In Aroma’s Journey

An aroma molecule’s release from food is the start of its journey to the olfactory area. The air carrying it and the route it follows are also part of the process. Air moved by breathing affects the direction in which volatiles around the mouth travel. Listing an ingredient’s volatile compounds therefore does not explain every part of the aroma perceived during eating.

Ni and colleagues investigated this transport question with a physical model in 2015. They produced a model of the upper airway from computed-tomography images of one healthy individual. Inward and outward flows interacted differently with the space behind the mouth: outward flow helped entrain volatiles from this region into the air stream.

The decisive detail in this single-person airway model is the meeting of cavity shape and flow direction. A volatile molecule’s journey continues after leaving the food: the geometry behind the mouth shapes its passage with the breath.

The Vanilla Experiment: Does Timing Matter As Well As Route?

The timing of an aroma’s arrival alongside a taste can be tested as well as the route its molecules follow. In 2017, Kakutani and colleagues used apparatus that synchronised odour delivery with participants’ breathing. Participants rated the sweetness of sucrose solution while vanilla odour was delivered through the mouth or nose, before or after drinking. The setup allowed a controlled comparison of odour route and the order in which smell and taste met.

In the first experiment, the ten participants included in the analysis rated sweetness higher when vanilla arrived retronasally after drinking. The same increase was absent when delivery order changed in the second experiment. Six of its eight analysed participants had also taken part in the first, so the comparisons largely shared their participants.

The vanilla–sucrose setup investigates how delivery route and timing contribute to sweetness ratings. The authors discuss the possibility that participants also expressed odour intensity on a scale provided only for sweetness. This makes the quality named by the scale part of the experimental question. Considering route, sequence and scoring together allows a closer examination of when flavour takes shape.

From An Aroma’s Name To The Whole Flavour

‘Fruity aroma’ describes a smell; it does not identify a particular compound or its quantity. A laboratory’s volatile-compound list likewise does not contain a dish’s entire sensory portrait. A compound’s presence in food, transport to the nose and perception during eating are connected stages of one process.

The smell rising from a bottle, the aroma within a bite and the volatiles found in a laboratory are different encounters with the same sauce. The retronasal route gives the second its name. Describing pepper aroma alongside sourness, heat and texture begins to connect that molecular journey with what we experience in the mouth.

• The distinction between umami and aroma
• Documented examples of peppers in desserts
• From a sensory description to a judgment of taste