The sense of smell or olfaction is evoked by scents, which are airborne molecules that are volatile enough to reach the olfactory receptors located at the top of our nostrils. Volatile stimuli can be perceived directly via the orthonasal pathway (directly through your nostrils) or indirectly, via the retro-nasal pathway when the wine is already in your mouth.
This is why wine perceptions are 80% olfactory in nature, because of these two ways of stimulations. Wine can account more than a thousand of volatile compounds that can evoke thousands of different aromas. Isn't it what we call complexity?
They are ciliated cells gathered at the top of the nostrils in a small area no larger than a standard mail stamp. The ciliae are very important as they contained the entry way to the olfactory system.
The stimuli need to be airborne to land on the cilia and find the right key to stimulate the specific receptor that will convey the signal for the taster to start detecting the aroma and recognize it. Of course the more intense is an odor, the more numerous are the stimuli to activate these receptors and get attention of the taster.
The mucus generated will block the pathways and prevent the odorants to reach the ciliae.
It is better to avoid tasting when you have a cold or allergy symptoms.
I found rinsing my nostrils with saline water helpful to clear the nasal passages and allow me to use my sense of smell.
While there are cases where a given volatile compound is the signature of a given aroma perception, most of what we perceive when smelling a glass of wine is the result of combined compounds and their equilibrium with the other wine constituents.
This represents a challenge for us sensory scientists when we train people to identify the various aromas in wines. We like to use aroma standards that can evoke specific perceptions, whether they are pure compounds, or food flavours, or actual products. Below is a table showing some examples of these standards (Table 1).
Many chemists have tried to decipher the relations between a molecule structure and its olfactive quality. This is not easy. A same aroma can be evoked by molecules of very different structures. On the same vein, two molecules with very similar chemical structure can evoke very different aroma perceptions.
Carvone can exist under two configurations. Configuration R smells like Spearmint while Configuration S smells like Caraway.
These two configurations are likely received onto different olfactory receptors to evoke such different aromas.
Our ability to detect aromas vary tremendously among individuals. The detection threshold, or the molecule concentration for which we start detecting a smell, varies a lot for most wine aroma compounds.
This graph illustrates how an odor threshold can vary among people from the same generation or age group and vary also among generations - as we get older, our sensitivity decreases.
These articles may also interest you. Just follow the links.