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Olfaction, the sense of smell, enables you to perceive the vast array of wine aromas 

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 stimulation. Wine can account for more than a thousand volatile compounds that can evoke thousands of different aromas. Isn't that what we call complexity?

Receptors for olfaction

They are ciliated cells gathered at the top of the nostrils in a small area no larger than a standard mail stamp. The cilia are very important as they contain 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 from the taster.

Why can't you smell when you have a cold? 

The mucus generated will block the pathways and prevent the odorants from reaching the cilia.

It is better to avoid tasting when you have 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.

Aroma Quality

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 flavors, 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.

Researchers at the Monell Chemical Senses Center are part of a collaborative effort to develop a mathematical model predicting if a molecule has an odor and what type of odor. This is an international collaboration, where scientist used AI, artificial intelligence, to develop models from an existing data set.

More details are provided in this article.

Olfaction skills vary among individuals

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.

Wine Aroma Kit

Wine Dictionary 

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