Why do people have different reaction to the same food? Some people love durian, but most people hate it! That distinct smell is so overwhelming that even many apartment building management companies throughout Southeast Asia have made strict policies against residents bringing it into their homes! 

In the West, many people love that potent flavor and aroma of ripe and sour blue cheese, a common side dish with cold cut meats that are served with red wine, but still many other people think it’s gross. 

These differences in preference could be caused by many different factors, such as smell, color, texture, and even temperature! All these factors combine to create the flavors of different food. 

The flavors of the food we experience are a combination of tastes and smells. As you may know, the human tongue can distinguish five basic flavors: salty, sweet, bitter, sour and umami. 

What most of us might not realize, however, is that our sense of smell is far more colorful. Studies have shown that humans have over 10 million olfactory receptors which allow us to taste over 10,000 smells. People usually think that flavor is mainly perceived with the tongue, but we have learned that our sense of smell is actually far more impactful. 

The most obvious example is when you have a cold.  Most of have probably realized that when you have a cold and try to eat, there’s no flavor to the food. This is because the nose is stuffed up, and there is no flow of smell or odors back to the nasal receptors and so you will notice some foods tasted different. Without smell, foods will taste bland and have nearly no flavors.

Try to pinch your nose closed to stop the flow of air through your nose, and put a piece of fruit, like an orange, on your tongue. You can taste some flavors, like sweetness from the sugar, or the sense of touch will give you a sense of the texture, but without your sense of smell, you might not pick up all the citric notes.  When you unpinch your nose, you will be overwhelmed by the strong citric aromas.

When you unpinch your nose, without realizing it, air will shoot from the back of your mouth through the nasopharynx (above the nasal cavity above the soft palate) to the smell receptors in the nasal cavity to stimulate your sense of smell. In fact, the diffusion of the volatile molecules in the air through the nasopharynx will account for much of the sense of smell. 

Interestingly, as we chew, food is moved around our mouth by the tongue, and this pushes volatile molecules from the food back to the smell receptors through the “retro-nasal route”. It has been said that only humans can roll the tongue, and that ability may impart special capabilities in manipulation as we chew and sense our food. At the same time, tastes are sensed by taste buds on the tongue, to the back of the mouth, and then into the pharynx.

Look back to the experiment, we can tell many key things about the role of smells in perceiving flavors:

1. Smell is a major component of flavor! 
2. The ability to identify the type of flavor is attributed to the combination of smell, and the taste and the sense of touch. 
3. Retro-nasal smell is significant but easily fused with taste and smell, so it’s not easy to recognize. 
4. Not only is smell not recognized as a part of flavor, flavor is generally not even recognized as coming from nose. Generally it is perceived as coming from mouth. The tongue has stolen the show!

References:

"Neurogastronomy: how the brain creates flavor and why it matters”, Gordon M. Shepherd, Columbia University Press, 2013. P29-45

“Evidence for glutamate as the olfactory receptor cell neurotransmitter”, Berkowicz, D.A.; Trombley, P.O., Shepherd, G.M., Journal of Neurophysiology, 71(6)