It is often said that "tea without bitterness and astringency is not tea." Bitterness and astringency are the original flavors of tea, as evidenced by the ancient name for tea, "bitter tea." However, tea connoisseurs are not savoring the bitterness and astringency per se, but rather the sweet aftertaste and salivation induced by the tea, experiencing the impact of the tea soup on their taste buds. The sweet aftertaste and salivation from tea originate from its bitterness and astringency.

1. The Main Components of Tea Leaves and Their Contribution to the Taste of Tea Soup:

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

Amino acids provide a fresh, brisk taste and are important components of the tea soup's flavor.

The main component of alkaloids is caffeine, which has a bitter taste and is also a crucial element of the tea soup's flavor.

The main component of tea polyphenols is catechins, also known as tea tannin, which impart bitterness, astringency, and a收敛性 (convergent quality), and are likewise vital to the tea soup's taste profile.

2. Explanation of the Taste Transformation from Bitterness/Astringency to Sweet Aftertaste and Salivation:

The primary substances forming the bitter taste in tea soup are caffeine and tea tannin.

The primary substance forming the astringent taste in tea soup is tea tannin.

The bitterness from caffeine does not linger long on the tongue; it dissipates quickly. This bitterness forms the foundation for the "sweet aftertaste." When the bitter substances no longer remain on the tongue and dissipate, it can lead to a change in taste perception, creating a taste "illusion" of sweetness returning. This illusion is likely a reflection of a basic human need. Fortunately, tea tannin can slow down the effect of caffeine, causing this instinctive illusion to linger in the mouth and on the tongue. This is the reason we often hear about "tea's addictive quality" or "getting hooked on tea."

The astringent sensation in tea soup is due to its tea tannin content (i.e., catechins). Tea tannin has a收敛性 (convergent/astringent) effect, causing proteins in single-cell microorganisms in the mouth to coagulate, thereby contracting local muscles in the oral cavity. When the bitterness and astringency of tea tannin dissipate, its收敛性 transforms, and the local oral muscles begin to recover, presenting a sensation of salivation (生津). If the收敛性 of tea tannin is too strong, intense astringency can over-stimulate the taste buds, lingering unpleasantly on the tongue. Often, this astringency accompanies bitterness, making it disagreeable. This kind of bitterness and astringency mainly results from improper tea processing and represents a significant flaw in the tea. The physicochemical properties of caffeine are relatively stable and generally do not change much during tea processing. In tea soup, tea tannin combines with caffeine, moderating caffeine's physiological effects on the body. Tea tannin can slow down and prolong the stimulating effect of caffeine. This is the reason we often hear that "tea refreshes the mind and dispels drowsiness."

3. The Taste of Tea Soup and Differences in Personal Evaluation:

The main taste-presenting substances in tea soup are amino acids, alkaloids, and tea polyphenols. Differences in the content of these three substances lead to variations in the overall taste experience.

The bitterness/astringency of tea soup and the subsequent sweet aftertaste/salivation are interconnected and inseparable, much like the concept of mutual promotion and restraint in the Five Elements theory. Without promotion, 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 promotion and restraint can things develop normally.

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

Personal Sensory Evaluation Criteria:

If there is bitterness upon entering the mouth, it should be at a level personally acceptable, and this bitterness should not linger on the tongue but dissipate and turn into a sweet aftertaste. If there is astringency upon entering the mouth, it should not cling to the upper palate, teeth, or lips, and this astringency should not linger on the tongue but transform and lead to salivation.

This is what I often say: Bitterness should not "sting" the mouth; astringency should not "cling" to the tongue.

What we usually refer to as personal taste is actually a subjective sensation—a comprehensive subjective feeling formed by the stimulation of our personal sense of taste, smell, and touch by the tea soup. Therefore, tea appreciation also varies from person to person.

A good tea is one where the fresh, intrinsic essence of the tea soup is so strong that it overpowers the bitterness and astringency, and where the bitterness and astringency transform almost imperceptibly. However, this imperceptibility lies in the individual's subjective feeling. This is the reason we often hear that "encountering a good tea requires缘分 (fate/affinity)."