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Taste, smell and flavour: How it all works

We explain why we taste things the way we do, and what ‘flavour’ really means.

The terms taste and flavour are often confused. ‘Taste’ refers specifically to the five basic tastes (tastants) that we perceive in our mouth. Taste is one part of flavour. ‘Flavour’, on the other hand, is the whole package: the combination of taste, odour and chemical sensations.

How does taste work?

We have taste receptors located within the taste buds in our mouths. Taste buds are found not only on our tongue but also on the side of the mouth, the soft palate, the cheeks, the back of the throat and even on our oesophagus. This is one of the reasons why wine tasters will swirl the wine around their mouths; to be sure the wine comes into contact with all the receptors for the maximum perception of the taste.

What are the basic tastes?

The only five tastes we can perceive in our mouths are sweet, sour, salt, bitter and umami. Umami (pronounced oo marmi) is a brothy or savoury taste, found when we eat bacon or miso soup.

How do we taste?

Contrary to popular belief, we are not limited to tasting sweet only on the front of our tongue, or bitter on the back, or sweet and salt on the sides of our tongue. In fact, we are all engineered a little differently. Because we now know there are taste receptors all over our mouths and receptors may perceive more than one taste, we may be able to perceive bitter on the sides of our tongue or on the oesophagus or cheeks. It is up to each of us to discover where we perceive different tastes within our mouths.

You can easily determine your own ‘tongue map’ by taking a solution, such as sugar in water, and swirling it around the mouth, noting where you perceive sweetness. Most scientists use caffeine or quinine for bitterness, salt for salty, sugar for sweet, citric acid or acetic acid (vinegar) for sour, and monosodium glutamate (popularly known as MSG) for umami.

Tastants need to be in solution (i.e. dissolved in water) to be perceived as taste. This is one of the reasons we salivate. The saliva ensures taste molecules are in solution, enabling them to remain in continual contact with the taste receptor nerve located within each taste bud. There is a pore at the top of each taste bud where the salivary fluid carrying the tastant binds to little hair-like cilia near the opening of the taste bud. These cilia stimulate the taste nerve, which then transmits perceptions to the brain. The brain interprets these stimulation messages as taste. Saliva also serves as a temperature controller so the taste molecules are perceived at body temperature.

We have on average 9000 taste receptor cells in our mouth. These cells last about 8 days. As we age the cells take a little longer to regenerate. This is also the case when we are sick. But the good news is the taste function remains fairly intact as we age, which is the not the case with our sense of smell.

The taste bud cannot be seen by the naked eye. The bumps we see on our tongue are actually called ‘papillae’. There are four types of papillae. Three are involved with gustatory (tasting) function and one is important in assessing tactile or ‘mouth feel’ characteristics.

Five basic tastes

There are only five tastes you can perceive in your mouth:

  • Sweet – like sugar
  • Acidic – like lemon juice
  • Bitter – like coffee
  • Salty – like table salt
  • Umami – like broth or bacon

Our sense of taste may have only five perceivable tastes, but our sense of smell makes up for this with an ability to perceive approximately 10,000 distinctive aromas. This is why odour is so important to the sensation of flavour. Research has found that our sense of smell accounts for 75-95% of a flavour’s impact. Have you tasted both grated onion and grated potato with a plugged nose? You would be hard pressed to distinguish between the two without the ability to smell them as well.

Over the centuries of human evolution, our sense of smell has been extremely important. Imagine if you didn’t have your sense of smell and you were trying to determine if your food had gone bad or was safe to eat! Smell protects us from getting sick or even dying (we can react to the smell of leaking propane gas!). Pregnant women have a heightened sense of taste and smell, which probably can be attributed to their evolution in protecting the unborn child from possible poisons.

How does smell work?

Scientists are still discovering how our sense of smell functions. In 2004, Linda Buck and Richard Axel received a Nobel Prize for mapping the entire genetic structure of the human olfactory system. They found there are about 1000 genes involved, which represents nearly 3% of the total human genome!

We all vary in our ability to perceive odours. Some people are referred to as anosmic, which means they have no ability to smell. This can be brought about by head injuries where there is damage to the olfactory nerves, impairing their ability to transmit information to the brain. Rugby players and other athletes who suffer numerous blows to the head and nose may experience a decreased sense of smell.  A severe head cold can cause a person to lose their sense of smell. Normally this condition is only temporary, although some people have reported the effects lasting from six months to a year.

People who suffer from cacosmia perceive all smells as something revolting, such as putrid or faecal. It is believed that these people suffer from a condition similar to epilepsy. Their brains cannot terminate signals from the olfactory nerves in the nose, and the perceptions of odour overwhelm the brain, with unpleasant consequences.  A rose will smell like vomit and freshly baked bread will smell like faeces.

People who lose or have an altered sense of smell have been known to suffer from depression. The area of the brain where we perceive odours is in close proximity to the pleasure area of our brain. We often smell a pleasant odour, such as freshly baked bread or scones, and associate it with happy memories.

Smell and emotion

In West Virginia researchers are studying aroma and what emotions they evoke. One study evaluated the effects of takeaways in your car. The odour produced by the takeaways evoked hunger, which in turn made subjects irritable even to the point of road rage. These same researchers also showed subjects smelling peppermint and cinnamon were able to improve their concentration and reduce their irritability while driving. The smell of lemon and coffee odours have also elicited improved concentration and clearer thinking.

Smell and memory also have a close association within the brain. Have you ever noticed that you can remember a smell from your childhood, say the way grandma’s house smelled? This ability appears to be linked by the close proximity of the smell area of the brain to the memory area of the brain. Recent studies have found that when subjects are exposed to a distinctive odour while they are learning new material, their subsequent recall of the learned material is improved when they are allowed to smell the distinctive odour once again.

How is odour involved with flavour?

There are two ways that the odour molecules come in contact with the olfactory bulb, which is located behind the bridge of your nose. Odours can be sniffed through your nose, which is referred to as orthonasal, or they can arrive at the back of the nose via the throat, which is called retronasal. While you are chewing a piece of cake, or sipping wine, the closing of your nose and throat as you swallow creates a vacuum at the back of your nose. This vacuum releases odour molecules from the food you are swallowing, and carries them from the back of the nose and throat and up to the olfactory bulb. Inhaling air through your mouth prior to and/or after swallowing will also carry odour-laden molecules in this retronasal fashion. Perhaps you’ve noticed wine judges making slurping and sloshing noises in their mouth when they are assessing a wine. Since the intake of the wine’s alcohol would quickly impair their judgement, they do not swallow the wine. Without swallowing the wine, they are apt to miss many of the taste components that would be released in the retronasal passage, so they must compensate by using various mouth agitation techniques to release the volatile taste components of the wine.

Orthonasal vs retronasal odours

  • Orthonasal odours come through sniffing.
  • Retronasal odours come through the back of the nose from the food in your mouth.

The last part of the flavour equation, chemical mouth feelings, are ‘irritations’ perceived by our trigeminal nerve. The trigeminal nerve fibres are located all over the mouth but are embedded under the surfaces of the papillae. Examples of trigeminal perceptions are the ‘burn’ sensations from chilli peppers or carbonated water, or the cooling sensations from menthol gum. The mouth-drying astringency of red wine or unripe persimmon is another. We have more trigeminal receptors than taste receptors in our mouths, but because they are under the surface, the nerve sensations are slowly perceived and are slow to dissipate. The problem with this delayed phenomenon is that the trigeminal perceptions will build when not enough time is allowed for them to dissipate. If you’ve ever been caught out by a hot chilli you will recognise the feeling: after eating a chilli it may take a minute for you to feel the heat, and by then you’ve eaten enough to build a strong, unavoidable sensation of pain in the mouth.

After prolonged exposure a person will become desensitised to the irritant. For example, if you worked in a chilli pepper manufacturing facility, you would eventually become less sensitive to the irritant qualities of chilli pepper.

Humans have a natural affinity for sweet foods. Other animals, such as cats, prefer salty items. Recent research has looked at how colour also plays a role in how well babies will eat. For example, if you feed your baby neutral-coloured foods, such as rusks and cereal, this will lead them to prefer beige and white foods. On the other hand, if you feed babies a wide range of coloured foods such as blueberries, carrots, feijoas and strawberries, they will have successful eating experiences with many coloured foods. This will mean they grow up to be less picky; they won’t be anxious about having a bad eating experience related to colour, and will learn to try many colours and types of foods.

Sensory science is a discipline that uses some or all of the five senses (taste, smell, sight, hearing, touch) to evaluate a product. Sensory laboratories are used by companies when they’re developing new food products, or making changes to old ones.

Scientists have attempted to duplicate human perceptions with a variety of measurement equipment. So far these instrumental attempts have failed to match the complexity and sensitivity of the brain and its receptors. There is also an important psychological and emotional component involved in human perception. To achieve reproducible, accurate and valid measurement data, sensory scientists rely on humans to assess a product’s sensory qualities.

In order to perform this measurement task a human (instrument) needs to be ‘calibrated’.  This calibration is achieved through a training process of introducing standards and having the panelists become very familiar with these standards. The panelists are required to remember and accurately identify the specific tastes, odours, colours, sounds or textures denoted by a specific descriptive term. An example of this might be having a panelist learn to associate a 4% sugar solution with the term ‘sweetness’. After the panelists attain a full understanding and recall ability for a descriptive term and its associated standard, they can then effectively evaluate products based on these attributes. The panelists measure the presence and intensity for each of the product’s attributes, and the data is collected to analyse a product’s attribute profile.

What are the secrets of a professional taster?

Professional tasters have a special area that is quiet and free from distractions. A setting as simple as the kitchen table is fine, as long as you can prevent distractions and interruptions.

Another important assessment practice is to cleanse your palate in between assessing samples. This helps you to ‘reset’ your senses back to ‘zero’, otherwise sensory overload or fatigue can alter your perceptive abilities. Cleansing also removes any residual product. Examples of palate cleansers used for tasting are: distilled/filtered water, soda water, unsalted plain cracker/biscuits, plain white bread, celery or apple. When you are assessing odours, sniffing a glass of unchlorinated water or smelling the back of your hand can be used as a cleanser.

Taste panelists must never wear colognes or perfumes. The brain will only consciously detect the perfume initially, but soon the signal will be dampened and the contamination effect will go unnoticed. There is a similar effect when you put your toe into a hot bath. At first your toe senses that the water is too hot, but eventually your brain stops reacting to this signal and the water does not feel as hot. If you are assessing a wine while wearing a floral perfume, your brain will dampen your neural response to floral notes, and may not perceive any of the floral notes in your wine.

Panelists also refrain from eating and drinking anything other than water for 30-60 minutes prior to tasting and smelling sessions. This is to ensure the senses are well rested. Coffee will effectively ‘paralyse’ the taste buds. Panelists also need to refrain from smoking 30-60 minutes before assessing a product. The commonly-held belief regarding smokers not being able to taste and smell as well as non-smokers has been proven to be a fallacy. Their ability is equal to non-smokers as long as they rest their palate from smoking before they evaluate a product.

A taster is not used to assess products when they are suffering with a cold or are sick. Their mucus congestion will dull their perceptions. It would be similar to looking into a microscope with a smudged lens; you might be able to see through but the image would be distorted. A professional taster is also never told what they are assessing so their personal attitudes and opinions about specific brands and other criteria do not influence their evaluation of the product.

Are some people naturally better tasters?

Some people are more sensitive to taste than others. Based on the number of taste receptors in our mouth we can determine if we are ‘non-tasters’ (25%), ‘tasters’ (50%), or ‘super tasters’ (25%).  Asian populations have a higher number of super tasters (35%). In Caucasian populations, women are more likely to be super tasters, (35% vs 15% of all Caucasian men).

So what does all this mean? Research has found that super tasters tend to not like overly sweet or bitter things such as Brussels sprouts, alcohol and coffee. If these people have something bitter such as coffee, they will put milk and perhaps sugar in it to counteract the bitterness. Super tasters normally have a lower body mass index, as they tend not to like overly fatty foods. Being thin may be the good side to being a super taster, but a bad side could be an increased risk of cancer. Since many antioxidants (like red wine and extra virgin olive oil) taste bitter and are often avoided by super tasters, current research is evaluating whether this group are at a higher risk.

Can you develop your sense of taste?

Concentration and memory are very important factors when learning to discern flavours. The difference between a wine expert and a novice wine taster is the wine expert’s ability to access and recall a mental library of flavour memories. This flavour memory can be acquired and developed in the same way that a person learns a new language.

You can improve your ability to taste and smell by performing simple exercises that help you to recognise and remember odours and tastes. Try covering several different spices with tin foil to hide their identity. Smell each one and see if you can correctly identify them. You can do it with wine also (albeit more expensively). Once you can correctly select a riesling, sauvignon blanc and a chardonnay in a blind tasting, your friends will be impressed! Eventually you will be able to develop a more extensive ‘library’ of odours in your personal odour library.

First published: Jun 2006



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