Tasting > Organoleptic characteristics > Smell

The sensation of smell is determined by the presence of volatile molecules in the nasal cavity. These stimulate the olfactive mucous membrane which is covered in a thin layer of mucus and is made up of sensory, basic and supportive cells and is also innervated with trigeminal terminations.

Sensory cells are actually nerve cells, appendices of the central nervous system and have fine hairs at the tip.

Molecules carrying smell excite directly the olfactive neurons by coming into contact with specific proteic receptors  present on these hairs.

There are no specific receptors for each single smell, although the presence of about thirty receptors of different types seems to have been proved, and each of these is able to recognise categories of molecules with particular characteristics.

The olfactive membrane performs best at around 37 degrees, which is the body’s own temperature.

The identification of smells is a rather complex phenomenon; in fact the single molecules, travelling along different routes to get to different areas of the mucous membrane, are perceived by generating different responses (moreover the stimulation of a certain number of specific receptors takes place in definite times of greater of lesser duration).

All of these factors makes it possible to perceive a huge number of smells.

In the case of nasal inspiration, the time the molecules spend  on the membrane is minimal since the air travels very fast through the nasal canals. In order to increase this time, retronasal inspiration is usually used, that is to say inspiration through the mouth with the consequent stripping of the odorous and aromatic molecules, and expiration through the nose.

The odorous molecules have characteristics in common:

1. high volatility, indispensable for them to reach the nasal cavity, to dissolve in the mucus and stimulate the olfactive mucous membrane;
2. liposolubility, which facilitates retention of the molecules in the membrane of the sensitive cells and therefore their link with the receptors;
3. a tendency to link with proteins (membrane receptors).

The ability to identify both the quality and the intensity of smells seems to increase with practice.

The efficiency of this training seems to depend on variables which operate together, for example a familiarity with odorous substances and the existence of a strong association between the smell and its name.

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