It is often said that "tea without bitterness and astringency is not tea." Bitterness and astringency are the original flavors of tea, and it has long been confirmed that tea was called "bitter tea" in ancient times. However, those who savor tea are certainly not tasting the bitterness and astringency alone; they are savoring the returning sweetness and salivation brought by the tea, experiencing the impact of the tea broth on their taste buds. The returning sweetness and salivation of tea originate from its bitterness and astringency.

1. The Main Components of Tea Leaves and the Composition of Tea Broth Taste

The main components in tea leaves are amino acids, alkaloids, and tea polyphenols.

Amino acids, which have a fresh and brisk taste, are important components constituting the taste of tea broth; the main component of alkaloids, caffeine, also known as theine, has a bitter taste and is also an important component of tea broth taste; the main component of tea polyphenols, catechins, also known as tea tannin, has bitter, astringent tastes and收敛性, and is also an important component constituting the taste of tea broth.

2. Explanation of the Taste Transformation from Bitterness/Astringency to Returning Sweetness and Salivation

The main substances forming the bitter taste of tea broth are caffeine and tea tannin. The main substance forming the astringent taste of tea broth is tea tannin. The bitterness of caffeine does not linger long on the tongue; it can dissipate quickly, and this bitterness is the foundation of "returning sweetness." When the bitter substances no longer linger on the tongue and dissipate, they can cause a change in taste perception, creating a taste "illusion" that presents as returning sweetness. This illusion should be a reflection of a basic human need. Fortunately, tea tannin can slow down the effects of caffeine, allowing this instinctual illusion to remain in the mouth and on the tongue. The often-heard phrases "tea is addictive" or "creates a craving" stem from this reason.

The astringent sensation in tea broth is because it contains tea tannin, which has a收敛性 effect, causing proteins in single-cell microorganisms in the mouth to coagulate, thereby causing local muscles in the mouth to contract. When the bitter and astringent taste of tea tannin dissipates and its收敛性 transforms, the local muscles in the mouth begin to recover, presenting the sensation of salivation.

If the收敛性 of tea tannin is too strong, the intense astringency strongly stimulates the taste buds and lingers unpleasantly on the tongue, often accompanied by bitterness, making it disagreeable. This kind of bitterness and astringency is mainly formed by improper processing of the tea leaves and represents a significant flaw for the tea. The physicochemical properties of caffeine are relatively stable and basically do not change during tea processing. In the tea broth, the combination of tea tannin and caffeine moderates the physiological effects of caffeine on the human body. Tea tannin can slow down and prolong the stimulating effect of caffeine. The often-heard phrases "tea refreshes the mind" and "dispels drowsiness" stem from this reason.

3. The Taste of Tea Broth and Differences in Personal Evaluation

The main taste-presenting substances in tea broth are amino acids, alkaloids, and tea polyphenols. Differences in the content of these three taste-presenting substances lead to variations in the overall taste. The bitterness/astringency and returning sweetness/salivation of tea broth are interconnected and inseparable, much like the concept of mutual generation and restraint in the Five Elements theory. Without generation, things cannot occur and grow; without restraint, things have no constraint and cannot maintain normal harmonious relationships. Only by maintaining a dynamic balance of mutual generation and restraint can things develop normally.

When we drink tea, we cannot determine the content of the three taste-presenting substances—amino acids, alkaloids, and tea polyphenols—let alone determine the proportion these three should follow.

Here is a personal sensory evaluation criterion:

If there is bitterness upon entry, it should be acceptable to one's personal taste, and the bitterness should not linger long on the tongue but dissipate and lead to returning sweetness;

If there is astringency upon entry, it should not stick to the upper palate, teeth, or lips, and the astringency should not linger long on the tongue but transform and lead to salivation.

What we often refer to as personal taste is actually a subjective feeling, a comprehensive subjective perception formed by the stimulation of the tea broth on one's sense of taste, smell, and touch. Therefore, tea appreciation also varies from person to person. Good tea is when the strong, fresh, and brisk original essence of the tea broth overshadows its bitterness and astringency, and the bitterness and astringency transform without the drinker even being consciously aware. But this lack of awareness lies in the subjective feeling of the individual. The often-heard phrase "good tea requires fate" stems from this reason.