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How do we smell?
The sense of smell is called Olfaction. It includes the detection
and perception of chemicals floating in the air. The role of the
olfactory bulb in smell was revealed by Ramon y Cajal, a Spanish
neuro-atomist, in 1890.
Chemical molecules enter the nose and dissolve in mucous within a
membrane called the Olfactory Epithelium. In humans, the Olfactory
Epithelium is located about 7 cm up and into the nose from the
nostrils.
When a smell enters the nasal cavity, it meets receptor neurons.
Humans possess approximately 10 million olfactory receptor cells.
Each receptor end is a swelling, or knob with approximately 5 hairs
(Cilia).
These receptor neurons then convert the smell into a message that is
sent to the olfactory bulb (which is seen as part of the forebrain
and its main sensory input).
The processing of the smell begins here, and is then passed onto
other areas of the brain like the limbic system that control
emotions, behavior and basic thought processes.
About 95 per cent of the nasal cavity is unrelated to smelling and a
very small amount of air actually reaches the olfactory bulb. We
have to inhale, and increase the velocity of our air intake to smell
things. The lightest molecules travel farthest and large molecules
have less smell. |
Mixed bag
The fragrance industry is actually like a box of assorted candies. It
contains a wide range of related industries. It includes the flavour
-makers—because the sub-stances used in creating taste and conjuring up
smell are mostly common. There are companies which manufacture smell out
of natural resources like plants and animal extracts Then there are
chemical industries which develop fragrances from synthetic chemicals.
Again, there are some industries which
sell products formulated only for their aroma—like perfumes and spices.
And there are others which market functional items like deodorants,
soaps, detergents, to which fragrance has been added.
Making aroma
Producing the right smell is a highly specialised tech-nology, that
involves several intricate processes. A team of experts ranging from
‘creators’ who select the raw materials, to skilled technicians and
chemists who analyse and synthesise the ingredients take part in
different stages of production.
This is how it is done.
The aroma ingredients, that is, extracts from flowers, fruits,
vegetables and other natural materials, usually have chemical functions
of alcohol, aldehyde, ketone or ester. Once the selection of materials
is made, they are separated, analysed, and synthesised in chemical
laboratories. Is the smell just right? Then comes the most important
stage—olfactory evaluation. Some aroma chemicals are produced in a
fairly large scale while numerous others are manufactured in a very
small volume. So it is absolutely critical to measure odour, in order to
ensure that what is being cooked up will appeal to the nose!
Many sophisticated devices and
apparatus have been developed in the state-of-the-art production units
of the upmarket smell-makers. But the final directive is still issued by
the highest authority—the human nose. So all fragrance companies have
their panel of ‘sniffers’—trained professionals with sensitive snouts,
who can distinguish thousands of odours and retain memory from session
to session. The measurements are made by applying mathematical formulae.
The criteria set may vary—but the there
are four commonly used ones. They are: Intensity: what should be the
right quantity of the sample used?
- Aggressiveness: what is the amount
that may cause discomfort?
- Type: Is the smell floral, almond,
pungent, foul?
- Quality: described using a six
degree scale-from zero to five. For instance, if sample is a floral
one, this is how its quality will be described—not floral; does not
resemble the flower; resembles to a small degree; resembles
slightly; resembles the flower; is perfectly associated with the
flower.
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