After the tea soup cools, why does it become turbid? Why does some tea soup taste sour after cooling? Both questions arise after the tea soup cools.

Cooling Turbidity

First, the color of the tea soup, whether raw or ripe tea, is mainly determined by the theaflavins, thearubigins, and theabrownins in the tea leaves. As the names suggest, the color of the tea soup is determined by the color of these tea components. For both raw and ripe tea, a moderate tea color with uniform brightness is considered superior. When a tea has an appropriate content of theaflavins and thearubigins, the tea color will naturally be moderate and translucent. Excess theabrownins result in an inappropriate depth of color. Only good tea can achieve a good soup color. From this explanation, it is not difficult to see that good tea essentially contains theaflavins and thearubigins.

Tea leaves also contain caffeine, which affects the taste and flavor of the tea soup. In a relatively good tea, the complexes of thearubigins, theaflavins, and caffeine will dissolve in water and precipitate as the temperature changes. Immediately after brewing, the tea soup is clear. When the tea soup cools, it becomes turbid because the complexes become insoluble and precipitate when the water temperature drops below 40 degrees Celsius.

This is why it is said that turbidity after cooling indicates good tea.

Cooling Sourness

In terms of the normal taste of Pu-erh tea, sourness and rancidity have always been undesirable descriptors. There are two scenarios for sourness:

Sourness in ripe tea and sourness in raw tea after cooling. Ripe tea undergoes fermentation. Excessively high temperatures during fermentation can cause undesirable transformations of tea polyphenols and enzymes, producing acidic substances. This indicates a problem during fermentation.

As for sourness in raw tea after cooling, what is the reason? Raw tea does not undergo fermentation, yet it can develop a sour taste. This is because when fresh leaves are harvested, many tea farmers do not handle the initial picking properly. Typically, farmers use bamboo baskets or cotton/hemp bags to carry the fresh leaves they pick, allowing the leaves to breathe.

However, some farmers use woven bags. After picking, if the fresh leaves are compressed for a long time, it becomes difficult for them to breathe. Combined with high temperature and the release of their own moisture, the fresh leaves undergo slight fermentation to some extent.

Alternatively, after the tea is processed into dry tea, if the dry tea still contains more than 4% to 6% moisture, and many tea farmers also use woven bags to store the tea, the lack of breathability coupled with moisture regain can easily lead to slight fermentation. These are all potential reasons for the development of sourness in raw tea after cooling.

This is because the transformation of tea essentially involves the transformation of polyphenols and enzymes. Normal transformation results in the tea's normal taste, mouthfeel, and aroma. Abnormal transformation leads to some foreign or undesirable flavors upon drinking. No matter how good the raw material is, every step after the fresh leaves are picked has an important impact on the final quality of the tea product.

Explaining exactly which substances and how they transform falls within the realm of chemistry. Actually, for tea drinkers, it is important to understand which flavors are undesirable and foreign.