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Where does the flavor of tea come from? Read these tips and you can become a tea expert

Jun 20,2024 | taetea

When we drink tea, we often have such questions: Why do some teas taste bitter, some are astringent, and some are fresh, sweet and delicious? Where do these different flavors come from? How do we feel the difference between these flavors? Today we will talk about the origins of tea flavors once and for all, and you can become a tea expert in seconds after reading this.

1. How do you perceive taste?

It is generally believed that taste is mediated by receptor cells gathered in sensory organs called taste buds.
The taste system can identify five basic taste types: sweet, bitter, sour, salty, and fresh. The principle is that after the taste receptors bind to the taste molecules, the taste cell membrane depolarizes and releases neurotransmitters. The generated signals are transformed by the nervous system and transmitted to the brain. After integration by the nerve center, taste perception is finally generated.

2. Taste map

There is a widely circulated saying about basic taste: taste buds in a specific area of ​​the tongue are "specialized" in one taste. However, research has shown that each area of ​​the tongue can taste 5 basic tastes, but different areas have different sensitivity thresholds for each taste.
Generally speaking, the taste buds at the tip of the tongue are more sensitive to sweetness, the taste buds on the sides of the tongue are more sensitive to sourness, the front of the sides of the tongue are more sensitive to saltiness, and the root of the tongue and a small number of taste buds distributed on the soft palate are more sensitive to bitterness.
So, the real taste map should be like this:

3. Taste in tea

The main flavor attributes of tea are bitter, astringent, fresh, sweet and sour.
Among them, bitter, fresh, sweet and sour are basic tastes, which are perceived by taste cells.
Astringency is defined as the dry, rough and wrinkled feeling in the mouth, which can be felt when drinking tea, red wine, or eating unripe fruits and various plant protein derivatives. Although the brain areas activated by taste and astringent compounds are the same, astringency is mediated by the trigeminal nerve, which does not transmit taste information. Therefore, astringency is generally considered to be a sense of touch rather than taste.

4. The main ingredients of different flavors in tea

Now that we know how the taste of tea is perceived by people, let’s talk about the ingredients that give tea different flavors.

Bitter and astringent ingredients

Catechins

Catechins are the main flavoring substances of bitterness and astringency in tea. They are mainly divided into 4 types: epicatechin (EC) and epigallocatechin (EGC) are called non-ester catechins; epicatechin gallate (ECG) and epigallocatechin gallate (EGCG) are called ester catechins.

There are differences in the bitterness threshold and taste characteristics of catechins with different structures. For example, ester catechins such as EGCG and ECG have strong bitterness and astringency, while non-ester catechins such as EGC and EC have a mellow taste and a refreshing aftertaste;

In addition, the same catechins also show certain differences in the intensity of bitterness and astringency, such as EGCG is more bitter than astringent, EGC is more astringent than bitter, and ECG is equivalent in bitterness and astringency.

Theaflavins and thearubigins

Catechins can be oxidized to form theaflavins with a benzophenone ring structure under the action of polyphenol oxidase. Theaflavins and other oxidation products of catechins can be further oxidized and polymerized to form thearubigins.

These two substances contribute to the astringency of tea soup, among which theaflavins compounds have a rough astringency.

Flavonol glycosides

Common flavonols in tea are myricetin, quercetin, and kaempferol. Different aglycones and sugar groups form different flavonol glycosides. Flavonol glycosides usually present a relatively mild astringency in tea soup.

The astringency threshold of flavonol glycosides is much lower than that of catechins (190~930 μmol/L). For example, the taste thresholds of isoquercetin, astragaloside, and hyperoside are 0.65, 0.67 μmol/L, and 0.43 μmol/L, respectively.

Anthocyanins

Anthocyanins are flavonoid derivatives and are a type of natural water-soluble pigment widely found in plants. Anthocyanins in tea are not only colorants that affect the color of dry tea, soup color and leaf bottom, but also contributors to the bitter taste of tea soup.

Especially in the Zijuan tea tree variety, the anthocyanin content is as high as 2.7%~3.6% in the new shoots of one bud and two leaves.

Alkaloids

Alkaloids are an important source of bitterness in tea soup, mainly caffeine, theobromine, and theophylline.

Caffeine is the substance with the highest content. The relative content of Pu'er raw tea during 10 brewing processes is between 4.02% and 8.62%, and its taste threshold is 500μmol/L, which is a pure bitter substance.

In addition, there is a special type of purine alkaloids in wild tea germplasm resources - theophylline. Theophylline in theophylline is the factor that makes its buds and leaves taste extremely bitter.

Bitter amino acids

Most bitter amino acids are L-type amino acids. Studies have found that the bitter amino acids in green tea soup include isoleucine, leucine, phenylalanine, tyrosine, and valine, but due to their relatively low content, their contribution to the bitterness of the tea soup is relatively small.

Tea saponin

Tea saponin is composed of hydrophilic sugars, hydrophobic ligands, and organic acids. It is a mixture of triterpenoid saponins extracted from plants of the genus Camellia in the family Theaceae. Studies have shown that tea saponin has a bitter and spicy taste, but its contribution to taste is not yet clear.

Umami ingredients

Theanine, glutamic acid, aspartic acid

Theanine, glutamic acid, and aspartic acid are the main contributors to the umami taste of tea soup. Among them, theanine is the key substance that gives tea soup its umami taste, accounting for more than 50% of the total free amino acids.

In addition, umami is a complex taste that has a balance of sour, sweet, and bitter. As the concentration of theanine increases, the umami taste of tea soup will also increase. When the concentration of glutamic acid and aspartic acid is greater than 0.4 mg/mL, the sour taste of tea soup will increase with the increase of their concentrations.

Sweet ingredients

Sweet amino acids, sugars

Sweet amino acids include alanine, proline, and threonine.

Sugars include water-soluble sugars such as fructose, sucrose, glucose, and maltose, among which D-fructose is the sweetest monosaccharide. However, the content of water-soluble sugars in tea is not high (about 2%), and sweetness is not the main part of tea soup, but it can reduce the bitterness of tea soup and increase the viscosity of tea soup to a certain extent.

Sour ingredients

Sour amino acids, some organic acids

Sour substances mainly include sour amino acids and some organic acids, such as aspartic acid, L-malic acid, etc.

Among them, L-malic acid has the highest taste activity value and is the main sour ingredient of Gongfu black tea, followed by gallic acid and succinic acid. The content of organic acids in tea leaves accounts for 3% of dry matter. In addition, during the processing of black tea, the heavier the fermentation, the higher the organic acid content. Sour taste can suppress bitterness and have a delayed effect on the perception of sweetness.

5. Tea flavor wheel

Tea soup is a mixed system. In addition to high-content polyphenols, phenolic acids and other substances, which play a major role in the taste of tea soup, low-content substances such as free amino acids, organic acids, and soluble sugars can improve the overall taste of tea soup and enhance the quality of tea.
If the tea is similar, the taste does not have to be the same. Although these flavor substances have specific flavor properties, they also have synergistic and antagonistic interactions, which cause the multiplication and elimination of taste, and finally converge on the taste buds to form a unique tea flavor.
The Tea Research Institute of the Chinese Academy of Agricultural Sciences has also launched the "Chinese Tea Flavor Wheel" based on summarizing the flavor characteristics and commonalities of various teas.

Image source: Tea Research Institute, Chinese Academy of Agricultural Sciences

The Chinese tea flavor wheel is divided into three categories: concentration flavor type, sensory flavor type, and characteristic flavor type:
(1) Concentration flavor type refers to the different concentrations of the tea soup flavor, that is, the strength of the oral irritation. It is divided into four types: light, mild, mellow, and strong according to the primitive morphemes condensed from traditional terms;
(2) Characteristic flavor type refers to the four basic flavors that people can feel when tasting tea soup. It belongs to chemical sensation, including fresh, sour, sweet, and bitter;
(3) Sensory flavor type refers to the physical stimulation that people can feel in their mouth and taste buds when tasting tea soup. It belongs to physical sensation. Combined with primitive morphemes, it can be divided into five types: thick, thin, smooth, rough, and astringent.

Conclusion

The tea soup rolls in the mouth and dances on the tongue, sometimes sweet, sometimes strong, sometimes mellow... The richness and changes of tea flavors form its unique charm, which makes people unable to stop.
Knowing the reason is not only knowing the fact, but also knowing the reason. Through the above content, we clearly know the flavoring substances of tea flavor, which have certain guiding significance for the improvement of process technology, tea selection, tea brewing, etc. in the process of tea processing!

References:

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