A tea-flavored chemistry class, all the dry goods are here.

Last week, a tea friend asked Yi Chajun how to explain the "returning sweetness" in tea taste.

On the weekend, Yi Chajun talked with several experts about this topic and felt it necessary to start with the chemical essence of tea taste.

I heard that I want to talk about chemistry, and many of my friends feel this way.

Hehe, it will be a bit boring, but friends who love tea are definitely worth seeing.

How did the taste of tea come from?

Before chemistry class, let's talk about a tea friend's feedback on the taste of Anji white tea:

Anji white tea smells a little refreshing after the rain, and tastes fresh and refreshing, like the feeling of spring sunshine and the recovery of everything, like a young girl in full bloom, youthful and lively.

In the eyes of chemists, this passage actually only said two words: Qing! Cool!

The essence of this feature is that the amino acid content of Anji white tea is particularly high (generally more than twice that of ordinary green tea), which is in sharp contrast with other green teas, thus leaving a deep impression on this tea friend (sunshine, girl, etc.).

So, besides amino acids, what other important chemicals are there in tea? Look at the picture below:

Let's talk about it one by one:

① astringent taste

In chemical essence, astringency is not a real taste, but a physical contraction reaction produced by the contact of human oral mucosa with specific substances, so we generally call it astringency and irritation.

The main astringent substances in tea are polyphenols, which generally account for about 30% of all water extracts in the brewed tea soup, and are the well-deserved main body of tea taste.

For a kind of tea, it is not good to have more or less tea polyphenols. Less polyphenols, light tea soup and tasteless clear soup; Too many tea polyphenols, tea soup will be too bitter. It is estimated that no one likes it except the old tea drinkers with heavy tastes. Generally speaking, when the content of tea polyphenols in tea soup is about 20%, the concentration of tea soup is the best.

Speaking of polyphenols, I also want to mention the fermentation of tea. The so-called fermentation, in fact, is to use the enzymatic reaction of tea polyphenols to convert them into theaflavins, thearubigins and theabrownins. This change not only changed the color of tea and tea soup, but also weakened the astringency of tea and transformed it into a more mellow taste. The heavier the degree of fermentation, the less the polyphenol content in the tea soup, for example, the whole fermented black tea completely becomes a sweet alcohol group; If the degree of fermentation is light, it will become ever-changing oolong tea, and the entrance is still irritating with polyphenols; There is also post-fermented black tea, which tastes mellow.

② Bitter taste

Mainly caffeine. You are not mistaken, it is indeed coffee. In fact, caffeine is an alkaloid commonly found in coffee and tea. Because it was first found in coffee, it was named after coffee.

The content of caffeine in tea is about 4%, which is the first contributor to the bitterness of tea.

Moderate caffeine can eliminate fatigue and excite nerves, so when we say that drinking strong tea and bitter tea can refresh us, we mean the function of caffeine.

③ umami

In tea soup, amino acids account for about 3% of water extract, which is the main contributor to the fresh and refreshing feeling of tea. In some special varieties of tea, such as Anji white tea, the amino acid content can be as high as more than 7%.

For tea, amino acids are everyone's favorite. They not only neutralize the bitterness of polyphenols and caffeine in taste, but also evolve an ever-changing charming aroma, which is an indispensable part of high-grade famous tea.

④ Sweetness

The content of soluble sugar in tea is less than 2%, so sweetness is not the main taste of tea. But it can still neutralize the bitterness of tea to a certain extent and make the taste of tea more harmonious.

However, it should be noted that the fresh and sweet taste of high-quality tea is extremely elegant, which is by no means forged by some unscrupulous traders by sprinkling sugar powder and brushing syrup. This kind of tea often appears in black tea. Because it is not the original flavor of tea, it is often not sweet after one or two bubbles.

⑤ thickness

The content of soluble fruit acid is about 3%, which is also a kind of sugar in essence. It is listed separately because it has unique viscosity and can enhance the consistency of tea soup.

When brewing some high-grade and high-quality tea leaves, you can obviously see that the tea soup flows out of the cover bowl like satin, and a mouthful of tea soup is contained in your mouth, giving people a rich and heavy feeling. This is due to pectin.

The taste of tea soup is a comprehensive reflection of these odorous substances.

How to get a balanced taste

In essence, the whole process of making tea is to adjust the composition ratio of chemical substances in fresh leaves of tea to achieve the most satisfactory taste. Only by understanding the changing relationship in the chemical world can we really understand a tea.

Next, we try to interpret several tea problems from a chemical point of view.

① Why can Yunnan green tea only win the encouragement prize?

Because of insufficient congenital conditions.

Among tea varieties, the distribution of polyphenol content is: arbor tea > shrub tea, big leaf tea > lobular tea. The tea trees in Yunnan are mainly large-leaved species, so the content of polyphenols is much higher than that of shrub-lobulated tea trees in Jiangnan. As we said before, the main taste of polyphenols can be expressed in one word: astringency! So it's no wonder that Yunnan green tea has always won the encouragement prize in various famous tea competitions.

But God is always fair. When a door closes, it will open a window for you. Polyphenol content is not good for green tea, but we can ferment it to make black tea, so we have Yunnan red with excellent quality; We can also not drink it first, and wait for it to age slowly (post-fermentation), and then we will have the world-famous Pu 'er tea. It seems that the first person to play Pu 'er tea was mostly a chemical expert.

② Why is green tea as tender as possible?

Because the more tender the part, the higher the amino acid content.

Everyone has understood the benefits of amino acids, so I won't say more. Of course, there is a limit to gentleness. Old tea drinkers know that the best green tea is often a bud and a leaf, not a bud and a leaf. Why? Because a green tea is "delicious", it should be not only fresh and refreshing, but also mellow and foam-resistant, and there should not be too few polyphenols. Only when amino acids and polyphenols reach the best balance point can we drink the best fresh alcohol taste.

③ Why do mountains produce good tea?

Because the extracted substances of Alpine Camellia are richer and the polyphenol content is lower.

Alpine tea gardens are generally mild in climate, abundant in rainfall, cloudy, with high humidity and fertile soil. Under such conditions, the growth of tea trees is conducive to the accumulation of nutrients, while the formation of polyphenols will be inhibited to a certain extent (weak light), showing the characteristics of fat and tender appearance, rich aroma, rich taste and resistance to brewing.

④ Why is the quality of spring tea generally better than that of summer tea?

Because the content of amino acids and pectin in spring tea is high and the content of polyphenols is low, tea trees are more nutritious.

In spring, the climate is mild, the humidity is suitable and the light is weak. After a winter break, the substance of tea tree is more abundant, and the tea made, whether black tea or green tea, is more mellow and fresh, especially before tomorrow.

In summer, due to strong light, the polyphenol content rises sharply. Tea trees are generally thinner than spring tea, so the tea made is bitter and thick. Only by making fermented tea can we recover the disadvantage slightly.

⑤ Why doesn't oolong tea pursue tenderness as much as possible?

This is related to the specific technology of oolong tea.

Oolong tea is one of the six most complicated teas, and it also has specific requirements for the quality of fresh leaves. Don't be too old or too tender. You'd better put the leaves in the middle.

Too tender fresh leaves, with simple aromatic substances and low sugar ether content (why there are new things, haha, not much to explain, the aroma chemical composition of tea is far more complicated than the taste), can not make the ever-changing aroma of oolong tea; The content of polyphenols in tender leaves is high, and the oolong tea made is heavy and unsightly; Moreover, the technology of oolong tea focuses on the oxidation reaction process of enzyme, and the enzyme concentration in fine bud leaves is high and the activity is strong, which is difficult to control.

Fresh leaves that are too old are worse. The content of almost all effective chemical components in the old leaves is very low, and the tea made is light in taste, short in aroma and thick at the bottom of the leaves, which is absolutely impossible.

Finally, let's talk about returning to Gansu.

What the hell is Gan Hui?

This word is often associated with the sweetness, salivation and throat rhyme of tea soup.

Yi Chajun thinks that Gan Hui is a sweet and slightly bitter taste, with a long aftertaste in the mouth, and with the passage of time, the sweetness gradually exceeds the bitterness, and finally ends in sweetness.

Its sensory experience is mainly manifested as "slightly bitter in the mouth and sweet in the aftertaste" and "bitter with sweetness, and then the bitterness gradually disappears, and the sweetness gradually increases, and the sweet aftertaste is longer than the bitter".

In other words, the sweetness of tea soup is usually based on bitterness, and the sweetness of tea soup is produced after bitterness. Once it is sweet, there is no need to pay it back.

However, not all plants have such characteristics at the same time. For example, bitter gourd and lotus seeds are bitter, while licorice is sweet but not bitter.

It is easy to understand the bitterness before returning to sweetness, which is obviously the irritating reaction of polyphenols and caffeine, but the sweetness after that may be the result of different components.

One view is that amino acids and sugars in tea are exposed after the bitterness is diluted, showing sweetness.

② The other is due to the contrast effect of taste. Sweet and bitter are a pair of relative taste experiences. When we taste bitterness, we will be more sensitive to sweetness, so the newly secreted saliva will make people feel extremely sweet. But this doesn't explain why bitter gourd is only bitter after eating it.

③ In addition, Professor Wang Yuefei from the Tea Department of Zhejiang University has another saying: Tea contains tea polyphenols, which can combine with protein to form an impermeable membrane in the oral cavity. If the content of tea polyphenols is appropriate, a film with only one or two monolayers or bilayers will be formed. This film has a moderate thickness and has an astringent taste in the mouth at first. Later, after the membrane was broken, the local muscles of the mouth began to recover, and the convergence and transformation would show a sweet feeling.

This is what we often say about the bitter taste that can be melted.

Unfortunately, the answer to this question is still inconclusive in the industry. Now some scholars have begun to use advanced electronic nose and electronic tongue to measure the aroma and taste of tea. But facing the colorful tea sensory world, we can only say that our scientific research has just begun.

Thanks to many tea lovers for their ideas and materials for this article.

References: China Tea Classic, Tea Chemistry, Tea Review and Inspection, Tea Culture and Tea Health and related academic papers.