THE PROCESS IN MOTION

Which route does what we think we taste take?

Start the scene or choose a stage. The animation simplifies the mechanism; what follows gives the details and the available references.

▶ Play the process01Breathe in: the odor02Sniff: nine tenths of the air03Slurp, exhale through the nose: the aroma04What remains on the tongue

Breathe in: the odor

Above the cup, one breathes in. Volatile molecules, those that leave the hot liquid with the steam, rise through the nostrils to the olfactory epithelium, a patch of 1 to 2 cm² at the back of the nasal cavity. This is the orthonasal route, and what it delivers is called odor. At rest, only 10% of the respiratory airflow reaches these receptors.

Read the stages without animation

1. Breathe in: the odorAbove the cup, one breathes in. Volatile molecules, those that leave the hot liquid with the steam, rise through the nostrils to the olfactory epithelium, a patch of 1 to 2 cm² at the back of the nasal cavity. This is the orthonasal route, and what it delivers is called odor. At rest, only 10% of the respiratory airflow reaches these receptors.
2. Sniff: nine tenths of the airBy sniffing, the air is directed to the top of the cavity: 90% of the flow then reaches the receptors. This is the smell of the bag of ground coffee, or of the bowl's crust at the moment of cupping.
3. Slurp, exhale through the nose: the aromaThe liquid is drawn in with air, mouth closed, then one exhales through the nose. Volatiles rise from the back of the mouth to the same epithelium: this is the retronasal route, aroma in the strict sense. Paul Rozin showed in 1982 that the brain attributes to the mouth what reaches the nose by this route: we “taste” raspberry or jasmine without any taste receptor being involved.
4. What remains on the tongueVolatiles disappear with the steam. Non-volatiles, sugars, acids, chlorogenic acids (CGAs), caffeine, melanoidins, remain in the cup and on the tongue: they make the body, acidity, bitterness, astringency and length. A cup forgotten for an hour hardly smells of anything and still tastes of everything.

To remember: Almost everything we think we taste, we smell: the odor enters through the nostrils, the aroma rises from the back of the mouth, and the tongue keeps what does not evaporate.

In history: The training documents set the vocabulary on this distinction: “odor” for the direct nose, “aroma” for the retronasal route.

Read the full article and its sources ↓

Almost everything we think we taste, we smell. Volatile molecules reach the olfactory epithelium, 1 to 2 cm² at the back of the nasal cavity, by two routes. The orthonasal route, when inhaling: this is the odor, that of the bag of ground coffee or of the crust in the bowl. The retronasal route, when exhaling through the nose after taking the liquid into the mouth: this is aroma in the strict sense, and it is the route that creates the impression of flavor.

Paul Rozin showed in 1982 that the brain attributes to the mouth what comes from the nose by this route, which explains why we “taste” raspberry or jasmine in a coffee without any taste receptor being involved. The professional training documents set the vocabulary of the trade on this distinction: “odor” for direct nasal perception, “aroma” for retronasal perception, and they teach the gesture, drawing the liquid in with air, mouth closed, exhaling through the nose. At rest, 10% of the airflow reaches the receptors; when sniffing, 90%.

Rozin, Perception & Psychophysics 31 (1982), p. 397-401; Shepherd, Neurogastronomy, Columbia University Press (2012); professional training document, coffee odors and aromas, p. 3

This division overlaps with a chemical division. Volatile compounds leave the hot liquid, rise to the nose and disappear with the steam; non-volatiles, sugars, acids, CGAs, caffeine, melanoidins, remain in the cup and make the body, the acidity, the bitterness, the astringency and the length. A cup forgotten for an hour hardly smells of anything and still tastes of everything. Yang and coauthors point to a bias in their discipline: research has chased the volatiles, which gas chromatography has separated well since the 1960s, and neglected the non-volatiles, which nonetheless carry half of the perception.

The dimensions the literature has worked on least, body and persistence, are also the ones trainers have the most trouble getting people to perceive.

Yang et al. 2026, p. 14; LC ch. 16b and 17