How does smell affect the way we experience food?
We may think that food flavours depend mostly on what we taste on our tongues, but our sense of smell actually has a far more dominant role – between 75 and 95% of food flavour is believed to come from it. This makes sense: while we have only five basic taste receptors (sweet, salty, bitter, sour and umami), we can detect hundreds of different smells.
How do we smell food?
There are two routes by which odours reach the nasal cavity, where they are detected. In the orthonasal route, odours are inhaled up the nose (like the smell of freshly baked bread coming from the oven), whilst in the retronasal route, odours are released as we chew and travel up the back of the throat. According to Professor Barry Smith, Director of the University of London’s Centre for the Study of the Senses, we often experience food odours differently depending on whether we detect them orthonasally or retronasally. “For example, a runny cheese may smell disgusting but actually taste quite nice. Conversely, many people love the smell of coffee but find it disappointingly bitter to drink. Chocolate seems to be a rare exception: we find the smell equally pleasant whether we experience it orthonasally or retronasally.2 Perhaps that’s one reason why we like it so much!”
There is a smell to sweetness
Certain smells have an impact on the perceived sweetness of foods. For instance, some tomato varieties taste much sweeter to us than others, despite the fact that they don’t contain more sugars. Researchers have demonstrated that these varieties have high amounts of certain volatile compounds which increase the sweetness we perceive.
...and to creaminess
Besides taste, smells can also influence textural properties: a fact first discovered by shampoo makers. In general, ‘fatty’ smells (such as coconut and butter) are associated with thicker and stickier textures, whereas fresh ‘green’ smells, (such as green apple and almond) are associated with smoother and more fluid consistencies.3 That’s the reason why low-fat yoghurt manufacturers now use specific smells to recreate the creaminess of full-fat versions.
Learning this might make us feel cheated by yoghurt manufacturers, but we could also see an opportunity: using this knowledge could help us develop healthier treats that still feel indulgent. Being exposed to certain smells could also influence us towards better food choices. Studies in cafeterias and supermarkets found that when people were exposed for at least two minutes to the smell of an ‘indulgent’ food (for instance, cookies or pizza), they were less likely to choose unhealthy foods, compared with when they were exposed to smells of healthier foods (such as strawberries or apples). The researchers suggest that prolonged exposure to the indulgent scent activated reward circuits in the brain, which then reduced the desire to actually consume the food.4
The jelly bean test
You can see how important smell is for flavour by taking the ‘jelly bean test’. If you chew a jelly bean while holding your nose tightly, you will detect its sweetness but not its flavour. If you then release your nose, you will be able to sense the flavour, for example strawberry or pineapple. This is because the tongue only has receptors for the basic tastes - salt, sugar, bitterness, sweetness and unami. We experience more complex flavours by integrating these with smells.
Wasn’t taste enough?
If smell and taste both contribute to flavour, why do we need both senses? It’s generally thought that smell helps us to avoid foods that may harm us (for instance, rotting food or poisonous fruits). Smelling food also triggers the release of gastric juices and other secretions that prepare our body to digest food.5 Food odours may also influence energy regulation. In one study, researchers fed the same calorie-controlled diet to mice that were either ‘super-smellers’ or had no sense of smell. Despite eating the same amount, the super-smeller mice gained significantly more weight.6 According to the researchers, these results could indicate that one function of the olfactory system is to help regulate energy balance in response to sensory information and hormonal signals. The interaction between smell and energy seems to work both ways: hunger signals released during fasting appear to increase our ability to smell foods,7-8 potentially to help us ‘seek out’ high-calorie, energy-dense foods.
How does the future smell?
Various innovations have been developed to introduce more intense or completely new smells into our meals. These include the Aromafork: a fork with a capsule under the handle. This emits a steady stream of scent from blotting paper that is soaked in a flavoured liquid. Some experimental chefs serve their meals on top of charred wood, a bed of smoking straw, or bowls filled with hyacinths (which release scent when hot water is poured over them). Others use atomisers that spray scents or scented dry ice. Whisky experts even developed a scented moustache wax designed to maximise the flavour of specific drinks. More technical solutions include ‘The Madeline’ which acts as a ‘camera’ that can record food smells to enjoy again later. The device captures odours by sucking them over a porous resin material which absorbs your meal’s volatile particles.
Don’t take your sense of smell for granted! As those who lose it know only too well, our food experiences would be much duller and less exciting without it.