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Many people might think that astringency in tea comes from tannin. The fact is tannin only contributed partially to the astringency. There are two types of root cause of astringency. Besides tannin, the astringency comes from minerals too.

Difference between tannin and poly phenol

Summer or autumn tea is normally astringent. If you drink those teas with empty stomach, your stomach may have very uncomfortable feeling and sometimes you may even feel nauseous.
Many people might think that the astringency is one of the characteristics of black tea. Some of my customers told me that they cannot drink black tea because they have weak stomach. In fact, it has nothing to do with the black tea. Many black teas in commercial tea market are often made from the summer-harvested tea. The summer tea contains very distinctive type of poly phenol called EGCG. This particular poly phenol will conjugate with protein of our body. Because of this reaction, we feel astringency. The substance that have a property to conjugate with protein is classified as tannin group. The term tannin is not referring to the specific substance but a group of substance that gives tannin-ish reaction.
The spring tea contains very less EGCG. Therefore, the spring black tea does not give any uncomfortable sensation in our mouth and stomach too.

Mineral causes dryness on our tongue

There is another kind of astringency in tea. It happens when we drink oxidized tea. This type of astringency never cause problem with stomach but an irritating sensation and results in an immediate dry and chalky feeling in the mouth. Besides oxidized tea, this type of astringency is caused by the tea fried at very high-temperature or tea that is grown with lots of fertilizer or pesticide. This astringency has nothing to do with the tannin. In fact, it is caused by specific type of mineral.

Magnesium = Astringent

A familiar example to understand the astringency caused by minerals is canned drink such as canned beer packed in aluminium causes astringency. If you have a chance to compare side by side the same type of drink between can and glass or pet bottle, obviously the canned drink gives dryness on tongue. It is easily sensed if you compare Coca-Cola from can and PET bottle.

There are a number of minerals such as copper, magnesium, silver, aluminium and zinc that gives astringency. I have studied the effect of each mineral in taste with water and tea. I noticed that the astringency caused by magnesium is exactly the same sensation as oxidized tea. If I add magnesium in green tea, it gives the same type of astringency as the oxidized green tea. Because of this finding, I started to think that magnesium is mainly responsible for the mineral-astringency in tea.

Tea contains a lot of magnesium inside chlorophyll

In fact, tea contains a lot of magnesium. Chlorophyll is the green pigment of tea, and it contains magnesium in the centre of its molecule. Magnesium is part of chlorophyll.

Mg located in the centre of the above molecule is Magnesium.

Chlorophyll is a very unstable substance, which means it is very easily oxidized. Once the oxidation takes place on chlorophyll, it will change into the substance called Pheophytin and magnesium will be released. We do not really get the taste of magnesium when it is bonded with organic substance such as chlorophyll. But once magnesium commes out, it greatly affects the taste. In particular, magnesium gives astringency and bitterness.

Gyokuro Tea Garden

I believe that the reason why the oxidized green tea gives strong astringency is due to the oxidation of chlorophyll. Similarly, the tea pan-fried at higher temperature also becomes astringent. High temperature during frying damages/oxidize chlorophyll and magnesium is released from chlorophyll.
Gyokuro and Matcha contains more chlorophylls than ordinary tea. It is because of these teas are produced under the shade and tealeaf needs more chlorophylls in order to effectively capture the sunshine. Therefore, the oxidized matcha or gyokuro gives much more astringency and bitterness than other teas.

The reason why black tea and oolong is not astringent

Black tea or oolong does not remain the chlorophyll. In these teas, chlorophylls are mostly oxidized and broken. However, black tea or oolong tea is not astringent unless these teas get oxidized. The magnesium in those teas may be forming a complex with other substance being formed during the enzymatic oxidation of poly phenol. Since magnesium does not exist in a free form, it does not contribute to astringent taste.

The reason why the fertilized tea is astringent

One of the reasons why fertilized tea is astringent is related to the amount of chlorophyll. If fertilizer is used, tea trees will grow faster and bigger. Consequently, it synthesizes more chlorophylls and conducts more photo-synthesis. Obviously, the fertilized vegetable or tea are so much greener due to higher content of chlorophyll.

Sustainable Tea Garden kept without fertilizer

On the contrary, the tea leaf of sustainable tea garden is yellow in colour. Because of no fertilizer is used, tea trees grow very slowly and thus it contain less chlorophyll. Tea tree require less photo-synthesis. It could be the reason why sustainable tea gives a clean taste with very less astringency.

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