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紅茶の発酵
The freshly-plucked tealeaf has green leafy aroma. When the fresh tealeaf undergoes appropriate fermentation or maturation, its green leafy aroma will becomes fruity or floral note. The fermentation of tea refers to the enzymatic oxidation, while the maturation means non-enzymatic oxidation. However, even if it undergoes fermentation or maturation, not all tea produces fruity or floral note.

Terpene exists both in fruits and teas

For both fermentation and maturation, poly phenol is the main substance in developing floral or fruity flavor. Poly phenol contains benzene ring with more than two hydroxyl substitutes (-OH) in its molecule. The major poly phenol found in tea is catechin, catechin gallate, epigallocatechin gallate and etc. When tea undergoes fermentation or maturation, poly phenol is oxidized and produced the substance called terpene, which is a group of substance, and isoprene is its molecular unit. Terpene also commonly exists in fruits and flowers. It is the substance that gives so-called fruity or floral flavor. The reason why the flavor of oolong or black tea is similar to the fruit or flower is because of these teas contain exactly the same substance as in fruit or flower. For example, the citrus note of oolong is because of the substance called geraniol, which also exists in citrus fruit. Another common substance in tea is called rinalool, which also exists in lavender or Bergamot. These terpene compounds are produced when poly phenol is oxidized through enzymatic or non-enzymatic oxidation. In other words, the more poly phenol the tea contains, the more floral or fruity flavor it produces after fermentation or maturation.

The more fertilizer is given, the more amino acid is formed in tea

The poly phenol content in tea is reflected by the way of farming. I have studied the relationship between the dose of fertilizer and the amino acid or poly phenol content in tea. I found that the more fertilizer is applied, the less poly phenol is formed. The poly phenol content in natural farming tea (grown with completely no fertilizer) is about 3 times higher compare to ordinary tea that is grown with modern agricultural practice. On the other hand, the tea grown with plenty of fertilizer contains a greater amount of amino acid (e.g., theanine).

Umami gives no advantage in fermentation or maturation

In terminology of taste, the amino acid is called “Umami”. Umami in Japanese has two meanings, one is referring to the specific taste of amino acid and another meaning is delicious taste. Due to this confusing meaning, many Japanese misunderstood that the more umami, the better the taste and the better the quality. This misstatement is often seen in many tea articles too. In any case, talking about the fermented tea, the presence of too much amino acid and less poly phenol does not lead to the good outcome in flavor. Amino acid undergoes Maillard reaction when tea is enzymatically or non-enzymatically oxidized. The Maillard reaction is the oxidation between amino acid and either sugar or poly phenol.

Tea that is rich in poly phenol produces fruity or floral flavor

In the initial stage in the Maillard reaction, tea usually develops flavor which is slightly similar to the flavor of hot cake. However, after tea is aged for a long time, the flavor becomes a bit “fishy”, a typical smell of oxidized amino acid. It is due to the further oxidation and degradation of the nitrogen compound produced by the Maillard reaction. On the other hand, tea from natural farming practice contains very high poly phenol and low amino acid, and it will develops floral or fruity flavor as a result of long term storage. As for the aging of tea, pu-erh tea is the most famous and should be the well-known tea for aging. However, there are many other teas that give fruity or floral flavor if it is properly matured, such as Darjeeling, Oolong Tea and White tea. Even the Japanese green tea, tea will develop fruity flavor if it is well-matured under certain conditions. Most importantly, tea is rich in poly phenol. Many famous gardens in Darjeeling carry out the biodynamic farming that uses very less or no fertilizer for growing tea. That is why a number of Darjeeling teas have an intense fruity or floral flavor. On the other hand, generally Assam tea is grown with much more fertilizer than Darjeeling tea. It is one of the reasons that Assam tea often gives the aroma that reminds us of hot cake.

自然栽培茶

Natural farming tea

雲南省の自然栽培茶

Natural farming tea garden in Yunnan

Modern and well fertilized tea garden in Japan

Tea with strong aftertaste contains a lot of poly phenol

If we compare between natural farming tea and tea grown with fertilizer, the natural farming tea gives stronger aftertaste. If we start applying fertilizer to the natural farming tea, it increases the production output but drastically reduces the aftertaste of tea. In a way, the poly phenol content is always in proportion to the aftertaste of tea. The lesser the nitrogen fertilizer is used, the higher the poly phenol content and eventually tea has stronger aftertaste. If less or no fertilizer, the number of tealeaf on the tree is decreased, the size of tealeaf becomes smaller and the growing speed also slower. In the end, each tealeaf of natural farming tea accumulates more minerals. If one hopes for their tea to be matured well, it is important to choose the tea with strong aftertaste.

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