How does our sense of taste work?

Based on the information that is transported from the tongue to the brain, there are thought to be at least five basic tastes. 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 neurons. These include, for example, some protein building blocks like amino acids, and also alcohols.

Most things that taste sour are acidic solutions like lemon juice or organic acids. This sour sensation is caused by the hydrogen ions (chemical symbol: H+). released by acidic substances.

Most foods that taste salty have table salt (sodium chloride) in them. Other mineral salts such as those containing potassium or magnesium can also cause a salty taste.

Bitter tastes are brought about by 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 are 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.

So far, five basic tastes have been identified. But research on others is ongoing. There are probably some sensory cells that respond to fat. "Greasy" would then be the sixth basic taste. In addition, research is being conducted on tastes such as alkaline (the opposite of sour), metallic, ammonium chloride (salammoniac), and watery.

By the way: Hot or spicy is not actually a taste. Strictly speaking, 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.

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. There is one exception though: 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 before they enter the throat and are swallowed.

Tasting is a complex process in which sensory neurons produce nerve signals based on the flavors of the food you put in your mouth. This is what happens:

When you eat food, the substances that are responsible for the food’s taste come into contact with sensory neurons in the mouth. It activates these by binding to specific receptors (proteins) in the cell membrane of the sensory neuron. As a result of this change, the sensory neuron releases chemical messengers called neurotransmitters that activate other nerve cells. This is how information about a specific taste sensation is passed on to the brain.

The "transformation" takes place in the taste buds. These are clusters of many sensory neurons with a specific structure: They resemble an orange with segments arranged around the center. At the top of the bud there is a small opening filled with fluid. The food substances with flavors are flushed into this funnel. This makes sure that the substances are detected and analyzed by as many sensory cells as possible before they are swallowed.

The mucous membrane of the tongue contains many wart-like projections: the taste papillae. They contain several taste buds with sensory neurons. Taste papillae make the surface of the tongue much larger. As a result, there is plenty of space for taste buds – and for increased taste sensation.

There are three types of taste papillae, based on their shape:

There are 200 to 400 fungiform papillae scattered across the entire 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.

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 (receptors) are located on their surface that can be activated by substances that have flavor. The sensory cells are connected to nerve fibers that send these taste sensations to the brain.

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) and in the linings of their lips and cheeks.

About half of the sensory neurons 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 tastes from the different parts of the tongue are combined.

The other half of the sensory cells and nerve fibers are specialized, reacting to one basic taste only. It is the job of these cells to determine the intensity of the stimulus – 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.