Tea leaves must undergo specific processing after being collected, including rolling, fermentation, drying, and more. These steps determine the quality of various teas in terms of color, aroma, taste, and shape. The tea produced through these processes can have a strong or smooth mouthfeel, with flavors that are bitter, sweet, or somewhere in between. Everyone has their own favorite type of tea.

When tasting tea, have you ever experienced a “sour” flavor? What are the sour tastes in tea? Why does tea become “sour”? Which types of sourness are good, and which ones are not? Let's explore this together!

Wuyi Sourness

In some high-quality Wuyi rock teas, “Wuyi sourness” can appear during the natural maturation period.

In the mid-19th century, European and American tea experts discovered “tannin” (catechin) in rock tea and isolated “Wuyi acid.” Later, it was confirmed that Wuyi acid is a beneficial mixture of gallic acid, oxalic acid, tannins, and quercetin. In 1847, Loret separated “Wuyi acid” from Wuyi rock tea. In 1861, Hahsweitz confirmed that Wuyi acid is a mixture of gallic acid, oxalic acid, tannins, and quercetin.

Note the difference between Wuyi sourness and process-induced sourness. Wuyi sourness is “sour but not cloying,” whereas process-induced sourness can make one feel nauseous, which we might call “sour nausea.” Therefore, don't blindly pursue Wuyi sourness. As the saying goes: “Though Wuyi sourness is good, don't overindulge!”

Hence: Authentic Wuyi sourness is good, while “sour nausea” is undesirable!

Tieguanyin Sourness

The false sourness in Tieguanyin, known locally as “green sourness,” is due to insufficient fermentation time, i.e., when the leaves are harvested and processed on the same day. Another type of sourness is called “green king sourness,” which is truly obtained through semi-fermentation in traditional processing methods.

The “Tieguanyin sourness” mentioned by tea enthusiasts is likely a mild sourness with a slight astringency that extends from the cheeks to the throat, similar to the sourness felt after eating Sugar. It stimulates saliva production and creates a sense of astringency on the sides of the tongue. This is often seen in the first three infusions of Tieguanyin with prominent sourness, but such teas usually exhibit significant sweetness and depth of flavor!

“Delayed sourness” results from a new processing method, which itself is undesirable, let alone the resulting sourness.

Hence: Green sourness and green king sourness are good, while delayed sourness is undesirable!

Black Tea Sourness

In general, fermented tea will have a certain level of sourness. However, if the tea soup clearly tastes sour, it could be due to the black tea being piled too tightly or over-fermented during its production. Since black tea is fully fermented, if the fermentation is excessive or the timing is not well controlled, drying will result in a sour taste.

Additionally, if stored for too long, black tea can become damp and improperly preserved, leading to a sour taste. Another factor is the water temperature used when brewing the tea. Depending on the tenderness of the black tea, if the water is too hot, it can cause the tea to have a more noticeable sourness. Theoretically, a pronounced sourness in black tea is caused by processing errors and is therefore undesirable!

Ripe Pu'er Sourness

For Pu'er, ripe Pu'er naturally possesses the characteristics of sourness, sweetness, bitterness, astringency, fragrance, and smoothness. Its sourness can transform into sweetness, reaching the throat without locking it, and the tea soup is smooth. Additionally, it should have minimal pile odor, which is more evident in aged ripe Pu'ers. Some well-converted ripe Pu'ers exhibit a fruity sourness. (Desirable)

However, improper Piling process can also give the tea a sour and rancid taste. This negative sourness will feel untransformed and can cause a tightening sensation in the cheeks, creating an unpleasant experience. This type of sourness is generally disliked. (Undesirable)

Where Does the “Sourness” Come From?

The sourness in tea can be divided into positive and negative categories. The positive sourness in tea can be considered a manifestation of the active compounds in terms of taste. Negative sourness is often due to processing or storage failures.

Main Sources of Sourness:

1. Wild tea: Due to the nature of the raw material, it often has a sour taste.

2. Low-grade picking, with four leaves and old stems. Because the old stems are difficult to process properly, the finished tea is more likely to have a sour taste. Summer-picked teas can also develop a sour taste, as some regions enter the rainy season during summer, increasing moisture content.

3. During manual processing, shaking and smothering combined with prolonged smothering, or light processing and light rolling, can increase the likelihood of the finished tea having a sour taste.

4. During sun-drying, if the tea is not dried in a timely manner, it retains too much moisture, making the finished tea prone to developing a sour taste.

5. When tea enters fermentation, under conditions of heat and humidity or microbial involvement, if the fermentation process is not properly controlled and not dried in time, the finished tea can develop a sour taste.

From points 2 to 5, we can see that the main reason is the involvement of moisture, causing the tea to undergo anaerobic fermentation and form organic acids.

The presence of sourness in tea is not always indicative of poor quality, as it depends on the concentration in the tea soup and the balance of its components. Good tea should have a balanced expression of “sour, sweet, bitter, astringent, fragrant, smooth, heavy.”

Correctly understanding the “sourness” in tea and learning to distinguish between positive and negative sourness is essential knowledge for every tea lover.