The more you come to love wine, the more curiosity about its "aroma" will surely sprout within you.
Of course, aroma is regarded as important for other alcoholic beverages as well (even Awamori has its own flavor wheel), but wine might be the only drink where people from all over the world passionately debate about aroma.
Now, having arrived at this column, you must also be one of those captivated by the "aromas of wine."
Here, we will share some trivia you should know to enjoy wine aromas: the two olfactory pathways, "orthonasal and retronasal."
The Two Olfactory Pathways
When people hear "wine aroma," anyone might imagine "the scent of wine smelled through the nose."
However, it is said that we humans enjoy not only the aromas sensed from our nose (nasal cavity), but also the aromas that travel from the throat up into the nose after swallowing wine.
In other words, "two pathways" exist in our sense of smell.
First, the former pathway that senses odors entering through the tip of the nose is called "orthonasal (direct smelling)", and the latter pathway that senses odors traveling up to the nose after placing food or drink in the mouth is called "retronasal (retronasal smelling/flavor)".
Humans are said to be the only animals with these two olfactory pathways, and according to one theory, it is believed to have evolved so that after putting food in the mouth to verify its safety, we can confirm whether it has a favorable flavor.
Evolution for the unquenchable pursuit of delicious things.
As long as the retronasal pathway exists, it may have been inevitable that we humans would fall in love with wine...
Is Retronasal Olfaction Important for Wine?
Now, upon hearing that "the sense of smell has two pathways," some might think:
"If a wine has an aroma of pineapple, you smell it with your nose, and then you just perceive that same aroma even more in the finish, right?"
While that is certainly not wrong, our human senses are not quite so simple.
The retronasal pathway plays complex roles, such as expanding the various elements possessed by the wine and making the wine taste even more delicious.
Changes in Aroma
First, numerous odor molecules exist in wine, and these disperse into the air as the temperature rises.
Let's take a sip of wine into the mouth.
Because the temperature of the wine rises upon entering the mouth, it can be considered that, as a result, even more odor molecules contained in the wine vaporize.
This means that other aroma components beyond those felt during orthonasal olfaction can also be picked up via the retronasal pathway.
Next, let us look at the reaction with enzymes in saliva.
According to Kazushige Touhara, an authority on olfaction research, it has been suggested that a new aroma can sometimes be generated when enzymes in saliva react with Sauvignon Blanc.
This could also be happening with other wines, and it might be an interesting field if further research is pursued.
Furthermore, the effect of humidity on wine is fascinating.
Because humidity in the mouth is 100%, it is said that many odor components that could not be detected orthonasally become detectable through retronasal olfaction.
Although it may not be directly related to this topic, the fact that humidity affects wine aromas essentially means that the perception of aromas changes depending on the country or land where you drink it.
Isn't it an interesting topic that the quantity of wine aromas you can perceive might differ between a desert and a wetland?
The Synthetic Nature of Aroma
One reason why retronasal olfaction plays such an important role for us humans (in gastronomy) is the synthetic nature of aroma.
Since this might sound a bit difficult, let's break it down as simply as possible.
First, here is a brief overview of the olfactory system:
Odor molecules enter the nasal cavity
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Reach the olfactory epithelium
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Bind to olfactory receptors on the olfactory cilia
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Electrical potentials are generated
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Transmitted to the olfactory bulb
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Information is transmitted to higher brain areas
Although it is extraordinarily complex just for simply smelling an aroma (tracing it in detail is guaranteed to induce panic), one theory suggests that it became such a complex pathway because the sense of smell is vital for living creatures.
Now, the part we want you to focus on here is the final step: "Information is transmitted to higher brain areas."
The key point is that, ultimately, each part of the brain determines the intensity of the aroma, the recognition of its type, whether you like or dislike it, and so forth.
*(For example, when someone unfamiliar with sushi rice smells it, they might judge that it seems sour or decide whether they like it or not, but they cannot identify it as the smell of sushi rice; and having never eaten sushi rice, neither good nor bad memories will come to mind at all.)
Interlocking of Numerous Perceptions
First, in the case of orthonasal olfaction, it is an independent sensation originating from the nose.
Since it only captures aroma, it follows the aforementioned pathway for aroma recognition. (Meaning an independent perception specialized in aroma.)
On the other hand, retronasal olfaction is not independent because taste, sensations, and tactile perception are also added; "multiple senses" interlock to form a new flavor.
Because there are the five basic tastes felt on the tongue, tactile sensations (such as astringency), differences due to temperature, and aromas rising later on, various parts of the brain and body react individually...
It becomes a complex, synthesized perceptual representation integrating not only olfaction but multiple perceptions.
However, this is only the story based on wine alone.
What happens when you think about it in terms of food pairing?
The perception of flavors combining wine and food, the texture of the food, the five basic tastes, the aromas that pass through to the nose after swallowing...
It is such a complex phenomenon that thinking about it almost gives you a headache.
Yet, being able to enjoy things this way is all thanks to retronasal olfaction, and because we are human.
It really is a fascinating topic, isn't it?
Let's Experience It
Although we have explained the wonder of retronasal olfaction in theory, there is a way to easily experience its role.
That method is to "drink wine (or eat food) while pinching your nose."
It is best if you have wine, but if not, try preparing any food with a strong aroma.
The Nose-Pinch Test
Pinch your nose, hold your breath, and put wine in your mouth
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Be careful not to let your exhaled breath pass through your nose
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Swallow the wine
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Keep holding your breath for a few seconds
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Release your fingers from pinching your nose
That's all.
A variety of flavors should have rushed softly through your nose.
While you might have sensed elements like cold, warm, astringent, or soft, you likely could not discern the flavor very well until you released your nose.
Once again, it is precisely because of the retronasal pathway that we find wine and meals delicious and are driven by the desire to "experience that ecstasy again" (accumulating memories of deliciousness).
The Fascinations of Wine Are Diverse
The intriguing thing about wine is that it relates not only to grapes, winemaking, producers, terroir, brands, production regions, and aging periods, but also to "the human body's organs."
Of course, it also connects to history, the psyche, romance, and the realm of business; it is no exaggeration to say it involves all aspects of life.
This time, we introduced the two olfactory pathways, "orthonasal & retronasal," but olfaction and wine remain connected by a profound relationship.
If this has sparked your interest, why not explore the sense of smell as well?
References
Olfaction and Chemistry: The Sensibility of Odor
Neurogastronomy: How the Brain Creates Flavor and Why It Matters / Gordon M. Shepherd