What we refer to as “taste” is basically a bundle of different sensations. It is not only the taste perceived by the tongue. The smell, texture and temperature of food play a role too. The “coloring” of a taste happens through the nose. The flavor of a food can only be determined when taste is combined with smell. If the sense of smell is impaired – for instance, because of a stuffy nose – it is usually harder to taste things properly too.
What are the basic tastes?
Based on the information that is transported from the tongue to the brain, there are thought to be at least five basic qualities of taste. Most dishes are made up of a combination of different tastes. Some dishes taste sweet and sour, for example, while others are salty and savory. The basic tastes are:
When something tastes sweet, it’s usually because of sugar and or derivatives such as fructose or lactose. But other types of substances can also activate the “sweet” sensory cells. These include, for example, some protein building blocks like amino acids, and also alcohols in fruit juices or alcoholic drinks.
Most things that taste sour are acidic solutions like lemon juice or organic acids. This “sour” sensation is caused by hydrogen ions (chemical symbol: H+). Acidic substances release hydrogen ions when they come into contact with water.
Most foods that taste salty have table salt in them. The substance responsible for this taste is the salt crystal made of sodium and chloride. Mineral salts such as those containing potassium or magnesium can also cause a salty taste.
Bitter tastes are brought about by many very different substances. In total, there are about 35 different proteins in the sensory cells that respond to bitter substances. From an evolutionary standpoint, this can be explained by the many different bitter species of plants, some of which were poisonous. Recognizing which ones were indeed poisonous was a matter of survival.
The “umami” taste, which can be compared to the taste of a meat broth, is usually caused by glutamic acid or aspartic acid. These two amino acids are part of many different proteins found in foods, and also in some plants. There is a lot of glutamic acid in things like ripe tomatoes, meat and cheese. Aspartic acid is found in asparagus, for example. Sometimes glutamate (the glutamic acid salt) is used as a flavor enhancer. This is done to intensify the savory taste of foods.
Hot or spicy is not a taste
By the way: The sensation “spicy” is very often described as a taste. Strictly speaking, though, it is only a pain signal sent by nerves that pass on information about temperature and touch. Foods that are seasoned with chili powder activate “pain and heat” signals. This is caused by the substance capsaicin in chili peppers.
Fatty, alkaline, watery: What else can we taste?
Researchers are looking for other specialized sensory cells that pick up sensations besides the five established basic tastes. According to recent research, there are probably receptors that specifically sense fat. This would make “fatty” the sixth basic taste. Research is currently being done on these potential tastes too:
Alkaline (the opposite of sour)
Are there different taste areas on the tongue?
There is a long-held misconception that the tongue has specific zones for each kind of taste, where you can taste things like sweet or sour especially well. But this myth is based on an incorrect reading of an illustration of the tongue. You can still find these zones in many textbooks today.
Sweet, sour, salty, bitter and savory tastes can actually be sensed by all parts of the tongue. Only the sides of the tongue are more sensitive than the middle overall. This is true of all tastes – with one exception: the back of our tongue is very sensitive to bitter tastes. This is apparently to protect us so that we can spit out poisonous or spoiled foods or substances before they enter the throat and are swallowed.
All of the different tastes can be tasted everywhere on the tongue
What does tasting involve?
When you eat food, the chemical substances that are responsible for the food’s taste come into contact with nerve cells in the mouth. The chemical substance activates the nerve cell by changing specific proteins in the wall of the sensory cell. This change causes the sensory cell to release chemical messengers, which in turn activate further nerve cells. These nerve cells then pass the “taste” information on to the brain.
The many wart-like bumps on the mucous membrane of the tongue are where the taste-producing substance is transformed into a nerve signal. These bumps, known as taste papillae, contain many sensory cells with a special structure: Together with other cells, they make up a bud that looks a bit like an orange with its sections arranged around a center.
At the top of the bud there is a small opening filled with fluid. The chemical substances responsible for the taste enter this funnel-like space. This makes sure that the substances are detected and analyzed by as many sensory cells as possible before they are swallowed.
What are taste papillae?
The taste papillae are made up of many wart-like bumps under the mucous membrane covering the tongue. They greatly increase the surface area of the tongue and make sure that individual tastes can be perceived more intensely. So they have a kind of taste-magnifying effect. The papillae contain several taste buds with sensory cells.
There are three types of taste papillae, based on their shape:
Fungiform papillae are the most common: between 200 and 400 bumps are spread all over the surface of the tongue. They are mostly found at the tip and edges of the tongue, making these areas especially sensitive to taste. Fungiform papillae not only detect taste: They also contain sensory cells for touch and temperature. Each papilla has 3 to 5 taste buds in it.
Circumvallate papillae are very large and found at the base of the tongue, where the throat begins. Every person has only 7 to 12 circumvallate papillae, but each papilla contains several thousand taste buds. Circumvallate papillae are round, raised, and visible to the naked eye. They are arranged in a V-shape at the back of the tongue. Each circumvallate papilla is surrounded by a kind of trench containing many glands that “wash” the taste-producing substances towards the sensory cells.
Foliate papillae can also be seen with the naked eye on the edges of the tongue at the back of the mouth. There you can see several folds that lie close together. Our tongue has about 20 foliate papillae on it, each of which has several hundred taste buds.
What are taste buds?
Taste buds are the true taste organ. They have numerous sensory cells that are, in turn, connected to many different nerve fibers.
Each taste bud has between 10 and 50 sensory cells. These cells form a capsule that is shaped like a flower bud or an orange. At the tip of this capsule there is an opening to a fluid-filled funnel, known as the taste pore. This funnel contains thin, finger-shaped sensory cell extensions, which are called taste hairs. Proteins on the surface of the taste hairs bind taste-producing substances to the surface of the cell.
The taste buds are located in the walls and grooves of the papillae. Adults have between 2,000 and 4,000 taste buds in total. The sensory cells in the taste buds are renewed once a week.
Most of the taste buds are on the tongue. But there are also cells that detect taste elsewhere inside the oral cavity: in the back of the throat, epiglottis, the nasal cavity, and even in the upper part of the food pipe. Babies and toddlers also have sensory cells on their hard palate (on the roof of their mouth), in the middle of their tongue as well as in the mucous membranes of their lips and cheeks.
The final step in perceiving taste is sending signals to the nervous system. This is done by several cranial (brain) nerves. All information is carried along the cranial nerves to part of the lower section of the brainstem (the medulla oblongata). At that point there is a split: Some nerve fibers carry taste signals – together with other sensory signals like pain, temperature or touch – through several exchange points to your conscious mind.
The other nerve fibers bypass the exchange point for conscious perception and lead directly to the “sensory perception” parts of the brain that are responsible for our survival. Here taste signals are combined with various smell signals.
How many kinds of tastes are there?
About half of the sensory cells react to several of the five basic tastes. The only difference between them is different levels of sensitivity to the basic tastes. So each cell has a specific palette of tastes with a fixed order of taste priorities.
For example, one cell might be most sensitive to sweet, followed by sour, salty and bitter, while another cell has a different order of taste priorities. The full flavor only unfolds when all of the sensory cell signals from the different parts of the tongue are combined.
The other half of the sensory cells and nerve fibers are specialized, reacting to one taste only. The job of these cells is to pass on information about the intensity of the taste – for example, how salty or sour something tastes.
Assuming that there are five basic tastes and ten levels of intensity, that means that 100,000 different flavors are possible. Taken together with the senses of touch, temperature and smell, this results in a huge number of possible taste sensations.
Brandes R, Lang F, Schmidt R. Physiologie des Menschen: mit Pathophysiologie. Berlin: Springer; 2019.
Menche N. Biologie Anatomie Physiologie. München: Urban und Fischer; 2016.
Plattig KH. Spürnasen und Feinschmecker: Die chemischen Sinne des Menschen. Berlin: Springer; 1995.
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