Odour and Aroma – Defining Olfaction from a Sensory Perspective.
Many people use the term ‘aroma’ to describe how something smells, and ‘odour’ is often a term reserved for something that smells unpleasant. From a sensory perspective however, these terms can be used to describe a smell that is ether pleasant or unpleasant. In fact, the difference between aroma and odour is actually the way in which the smell chemicals, or volatiles in question, are being detected.
Let’s examine odour first. When we are asked what something smells like, our instinct is usually to sniff at the thing we are being asked about. By doing this we are pulling, or funneling, volatiles up our nostrils to our olfactory receptors. Another term for this is ortho-nasal olfaction.
So if odour is what we are smelling using our nostrils, what is aroma?
Aroma is in fact the term used to describe smell chemicals that have made their way to the olfactory receptors via the back of the throat, as opposed to via the nostrils. When we eat a food we chew it, break it up and warm it up. These actions have the effect of releasing volatiles from the food, which when we swallow are pushed up the back of the throat to the olfactory receptors. Another term for this is retro-nasal olfaction.
"Weg der orthonasalen und retronasalen Wahrnehmung“ by LC Uni Hohenheim is licensed under CCO 1.0
Our olfactory receptors are located on the lining of our nasal cavity at our olfactory bulb. When stimulated, the olfactory receptors transmit information to our brain for processing and to identify what it is we are smelling. You may have noticed that when you smell something it can often remind you of a place, experience, person, time, or other set of circumstances. This is due to the location of the olfactory bulb next to the limbic system of the brain which deals with memory.
Trillions of different odour compounds exist that can be detected by humans, and foods are made up of mixtures of these compounds e.g. a tomato can have around 400 different aroma compounds making up its olfactory character. These compounds are critical in our perception of products, as olfaction makes up between 70-85% of flavour perception. As you can start to see, olfaction is a very complex and important human sense.
Olfaction is also a very powerful sense when it comes to consumer acceptance of products. Pumping out pleasant smells like that of freshly baking bread into a grocery store has been shown to increase sales. Some restaurants provide atomisers of aroma compounds with specific courses, or smoke under a cloche that is released at the table to add an extra sensory dimension designed to heighten the diners experience. Take the flip side of that whereby if you walk into a restaurant and smell drains, you are likely to think twice about staying for a meal!
Image courtesy of John Placko, Modern Culinary Academy