Why does tea, a centuries-old Chinese beverage, have this bitter and astringent taste? The astringency primarily comes from tea polyphenols, also known as "tea tannins." These are a group of polyphenolic compounds in tea leaves, including catechins (flavanols), flavonoids, flavonols, anthocyanins, leucoanthocyanidins, and phenolic acids, collectively called flavonoid substances.

The astringent sensation is caused by tannins and other polyphenols interacting with salivary proteins and glycoproteins. Thus, astringency is not a taste perceived by taste buds but a tactile response stimulated by protein interactions.

In tea, bitterness and astringency often coexist, though one may dominate. Caffeine is the main contributor to bitterness, while the combination of caffeine and catechins forms hydrogen-bonded complexes. When both are present in high amounts, the tea tastes rich and refreshing.

Beyond natural compounds, improper processing or storage can intensify bitterness. Astringency arises from polyphenols, and fermentation plays a crucial role in balancing flavors. Over-fermentation or poor handling, such as excessive sun-withering or improper stirring, can lead to undesirable bitterness or a grassy taste. The key lies in adjusting techniques based on leaf tenderness, sunlight, temperature, and wind—summarized as "making tea according to the leaves."

As the Chinese saying goes, "Good medicine tastes bitter." Despite its initial harshness, tea's health benefits are invaluable. Embracing its complex flavors is a testament to life's wisdom for every tea lover.