Retronasal olfaction: the other way to taste aromas in wine

Isabelle Lesschaeve Author

80% of what we taste, we smell; however, retronasal olfaction is still a mystery to many wine lovers. Let’s demystify it.

Published February 27, 2023

I’m often surprised how little is known about the importance of retronasal olfaction in our wine tasting experience.

I was on a call with a reporter writing a piece on how to help people improve their wine-tasting skills.

Isn't it my mission in this world? Well, one of them, for sure.

What struck me, once again, was the realization that serious wine people didn't know that 80% of what we taste, we smell.

If this is your situation, know you’re not alone. I wrote this article to give you the full picture of what happens when you have a sip of wine.

Retronasal olfaction, or how to smell wine aroma in the mouth

When you smell a glass of wine, wine aromas reach your nose directly - what scientists call orthonasal olfaction. However, when you take a sip, wine aromas will reach your nose indirectly through the retronasal passage, as shown in this image.

Difficult to understand?

Here’s a short video showing you how you can experience retronasal olfaction with a simple trick.

The four ways you can smell wine aroma compounds in your mouth

A 2021 scientific study highlighted what happens when wine is in your mouth. I share the researchers' explanations in this video, and I summarize the main points below the video.

The study describes the four ways wine aroma compounds can reach your nose through retronasal olfaction.

1-Breathing in and out

When you breathe in and out, the airflow will carry the free aroma compounds through the retronasal passage to reach your olfactory receptors, as I described in the first video. This phenomenon is what we call retronasal olfaction.

2- Enzymatic action

Some wine aromas get only released once in your mouth.

The enzymes in our saliva will break down any aroma compounds bound to aroma precursors. Indeed, wine aromas come in many types: some are free to get airborne and reach your nose, and others are bound to other molecules called precursors.

The saliva enzymes will activate the reaction releasing the bound aroma compounds in your mouth.

This is why sometimes you don't perceive the same aromas that you have smelled because those aromas are bound when you smell and have no odors, but then are released in your mouth, thanks to the saliva action.

3- Microbial activity

The activity of microbes, usually present in our mouth cavity, can also help release the aroma compounds bound to the precursor molecules.

4- Absorption and resorption

Some aroma compounds tend to be absorbed by your mucosa, the cells of your mouth epithelium. But, after you swallow, these absorbed aroma compounds are let go, explaining some aromas' aromatic persistence

You don’t perceive them when the wine is in your mouth because they are bound and unable to get airborne to teach your nose. They get freed once you swallow and take a breath.

This graphic illustrates the four ways aroma compounds get released in your mouth and is the one I commented in the video.

Source: https://doi.org/10.1016/j.food...

Retronasal olfaction is a difficult concept to grasp

These four factors contribute to releasing certain aroma compounds in the mouth that you might not perceive directly from smelling in your glass. However, I understand that it’s difficult to realize, even for knowledgeable wine enthusiasts.

In the video, one of my students asked this question when I explained retronasal olfaction.

She said:

“I completely understand, you know, the saliva breaking down and the mucosa and everything. So it releases additional aromas you can't detect on the nose itself. But when you have the saliva proteins in the mucosa breaking down the aromas, is it still your nose detecting? Are you tasting the aroma or are you smelling the aroma?”

Me:

“I agree the explanation is a bit technical, but indeed we’re smelling through our mouth retronasal passage."

Student:

“But it's in your mouth, but you're smelling it?

Me: 

“Yes, indeed”

Student:

"Because you can really only taste like the bitter, sour, or sweet. So you can't taste leather or tangerine when you start describing wine in your mouth, but you're smelling it."

Me:

“Exactly.”

Like the wine magazine reporter, my student, a WSET Level 3 candidate, never realized the importance of retronasal olfaction. Even when we have a cold and can’t smell a thing, we often complain that our food or wine is bland, without any flavors.

The fact is that in our everyday language, we abuse the word taste to include many different sensory perceptions: the basic tastes perceived on the tongue and other organs (acid, sweet, salty, and umami), the physical sensations like the heat of alcohol and dryness caused by tannins, and the aromatic perceptions I just described.

Is this concept of retronasal olfaction new to you?

Contact me if you have any questions about improving your tasting skills. I’d love to help you.

Categories: Tasting education, wine aroma