Tea Fermentation

The fermentation process may be looked at from two points of view: the consumer’s view and professional one.


The main difference between the types of tea is fermentation rate

Type of tea Fermentation rate
Green tea 5%
Yellow tea 10%
White tea 15-25%
Light-roast oolongs 15-30%
Dark-roast oolongs 30-80%
Young sheng pu-erh (less than 5 years) 15-30%
Aged sheng pu-erh (less than 12 years) 30-60%
Old sheng pu-erh (12+ years) 60-100%
Shu pu-erh 90-100%
Black tea 70-100%
Red tea 80-100%

What do these numbers mean? Actually, nothing. And if they do, they’re wrong. But everybody loves to put them into every book about tea there is, so I decided to do it as well. After all, tables and numbers always looks seriously and trustworthy. But, let’s not get ahead of ourselves

The closer the leaf to its original state, being alive on a tree, the less fermentation rate it has .

Let’s break down fermentation with yet another book example:

How should we understand the fermentation in tea? Take several apples. Cut one of them into two halves, make shallow cuts on the skin of the second one, and leave the third one as it is. In 5 minutes cut off a slice from each apple and make your own assumption about taste and color changes. The cut apple will get darker, gain a bit brownish coloring, the smell will be slightly different and it will be a bit sweeter. Now the apple with shallow cuts will get darker more slowly, still being original inside and will contain all the flavors. And the third apple will be our reference standart taste product. These are the processes that may be compared to those running in tea.

I like this example for its simplicity, but in the same time I don’t like it for the deception. Apples have a high level of iron content that quickly gets oxidized, so they quickly turn brown. Tea is also brown and I’ve seen a lot of articles, that conclude tea having a lot of iron content that oxidizes and turns it brown, based on this example. However, it’s dead wrong. We’re going to review how it actually is in the second part. Now let us discover what exactly they do with different types of tea during the production

Different types of tea and different rates of fermentation. In most cases the darker the tea – the higher the rate of fermentation

During the production of green tea, they try to roast the leaf as quickly as possible, so the humidity wears off and all chemicals reactions, which may be going on in the leaf after it was picked, stop

During the production of yellow tea, for the leaf special conditions are made, so that the “green goes away”. In order to achieve that, the roasted leaves is put into a warm and humid room, and wait for the moment when the green disappears, so they can dry it out once again

During the production of white tea, the leaf is sun-dried. The process takes a few days, and while it is drying out, the chemical processes, that alter the chemical composition and making the leaf lighter and less green, are going on

During the production of light oolongs, they’re slightly damaged on the edges and given a small amount of time to ferment. Later, the tea is rolled and roasted, like green tea

During the production of dark oolongs the tea leaf is damaged harder and the amount of time to ferment is longer

Shen pu-erh is prepared in a similar way to green tea, but still the tea leaf is dried slightly less, and the tea itself is given a lot of time to ferment – years and decades. That’s why it’s hard to call fresh pu-erh fermented, and old ones are called “postfermentated”, meaning the fermentation process took place after the production

Shu pu-erh is prepared much like sheng puer, but they’re aged artificially at the last stage, creating perfect conditions for microorganism, like in a greenhouse: the tea is humidified with steam and covered with matting. So microorganisms got around 45 days to age tea leaf and make it look like very old sheng puer.

Black tea is basically sheng puer, cooked not in Yunnan, but in Anhui or Hunan where the leaf is smaller, so it ages faster.

Red tea is a tea that is specifically damaged as much as possible so that the fermentation processes occur as quickly as possible. In contrast to the pu-erh, here the producer controls the fermentation process completely and stops the fermentation for choice

By this point, we can conclude that fermentation is the result of the work of the tea producer. The more the producer "wizards" over tea, the more it is fermented. But if we look at the table, we will notice that many teas have the same rate of fermentation. Why do they then fall into different groups? The type of tea is determined by its recipe, and as a result we get a different rate of fermentation

Then what does this give us?/p>

From the regular people point of view, this gives us the understanding of the temperature mode the tea needs. The more the tea is fermented, the hotter water you need to use when brewing, the more tea you can put in a vessel and the more heat-intensive material you can use . So you can start using the hottest water beginning with the white tea, while and for the teas with fermentation of 50% and higher, you also should use thick-walled dishes, preferably made of good dark clay. Only the tea with fermentation above 80% makes sense to be boiled (though personally I do not like boiling red tea). Also, the less the tea is fermented - the better it is for long infusions. That is why dark teas, when infused in European style with long infusions in a large cup or teapot, are so tasteless and gross, and green tea on the other hand turns out to be soft, pleasant and saturated.

Great, now from the regular point of view we know what is called fermentation. But what really is happening with tea at the moment of treatment?


Let's look at the scientific part of the question and understand the chemistry of tea! And most importantly, let's try to understand how fermentation of the tea influences our body!

Fermentation is a type of agitation, in which, thanks to bacteria and enzymes inside the product, the sugar is converted to acids, gas and alcohol

Fermentation is involved in the production of wine, beer or other alcohol-containing products. And since the tea business is often put into one box with a winemaking, the used term is the same. Also, fermentation takes place during panification, milk products, some cheeses, etc

The processes through which we get different types of tea are:

  • Oxidation
  • Heating
  • Fermentation

Why these three terms have merged into the last one is a mystery to me. Depending on how these three processes will proceed, we will get different types of tea: white, green, yellow, oolong, red or puer

In the course of the above described processes, the chemical composition of the tea will be changing, but the most interesting substances for us are:

  • chlorophyll
  • catechins
  • theaflavin

As we all know, chlorophyll gives the leaves a greenish color and it is preserved in green tea. When the chlorophyll is destroyed, the leaves lose their beautiful green color, we first get a grayish leaf, which becomes more dark, purplish-brown in the further processing. Beyond that, chlorophyll has a distinct herbaceous taste, so green tea is associated with freshly cut grass

Chlorophyll molecule

Catechins are one of the most beneficial substances in tea. Catechins are antioxidants. A smart word that means “a substance that prevents the oxidation of molecules, including molecules in our body, as a consequence prevents the formation of free radicals and protects our cells from destruction”. Altogether, if you want to stay young and healthy the catechins is your friend. And where the largest amount of catechins is? In white tea! And the second place goes to green tea. And only after them such products as strawberries, apples, gooseberries and plums are. Catechins have slightly bitter taste, specific to green and white teas. White tea has the highest content of catechins among other natural products. So, 100 grams of dry tea leaf, the content of EGCG catechins alone, which will be discussed later, is from 4500 to 7500 mg, while 100 grams of apples have only 109 mg! Thus, to stay healthy, you can eat a kilo of apples every day, or drink a cup of white tea instead

Catechin molecule – epigallocatechin gallate (EGCG)

For the purpose of objectivity, let`s look on the negative side of catechins. Any medicine in this world, if used in high amounts, harms the human body. So, in the 80s of the last century, the scientists actively studied catechins and came to the conclusion that this is simply the manna of heaven: it heals the heart, lowers the cholesterol level, normalizes blood circulation, protects the liver tissue, and increases immunity, and as it turns out, it also helps with numbers of diseases, dealing with which was quite pathetic back in the days. Such diseases included viral hepatitis. Large doses of catechins deal with it perfectly, and back in 1983, the Catergen, 63% made of catechins, entered the market. The patients were prescribed huge doses of this drug and the consequences were swift - one of the patient’s kidneys failed. Later, the same symptoms were found in other patients and guess what it ended up with? Right, Catergen and other catechin-containing drugs were banned. At least 20 years of studies and scientific justifications by pharmacists have been carried out to bring catechin-containing drugs back to the shelves of pharmacies, which so many patients needed. In addition, their cost is lower and they are easier to get. In many countries, Catergen was not banned, but sold and successfully used to this day, but no one stumbles upon an idea to prescribe patients thousands of milligrams of catechins per day anymore. For the tea to have a negative effect, you will have to drink at least 9 liters of tea a day for one week, and only white and green, which is probably a hard task, but if you suddenly decide to try, I'll ask you not to do it

Catechins can be of different types. One of the forms of catechins in tea is EGCG. It is remarkable in that it can significantly slow down the growth of cancer cells and thereby helps the immune system of the body to fight cancer cells independently. Therefore, white and green tea is really beneficial during the cancer treatment, as it won’t interfere with other drugs and other forms of treatment, and most importantly - regular consumption of white and green tea ten times reduces the risk of a tumor appearance. Studies are still being conducted on this subject and it is too early to talk about a miracle cancer cure. But, a group of scientists from the Moffitt Cancer Center in Florida, USA, conducted a study involving 97 prostate cancer diagnosed men. The men were divided into two groups, one of which was given decaffeinated green tea, and the other one was given a placebo. The result of examination of the first group showed the lower content of KLK3 (PSA) being a tumor marker. It makes one sure that tea really helps to fight cancer. It is simply a phenomenal result for medicine. I won’t pretend like I have obtained a second medical education in oncology and I won’t ask you to take my words for it, but I'll give you the opinion of the doctors who conducted this study “Randomized, Placebo-Controlled Trial of Green Tea. Catechins for Prostate Cancer Prevention” to examine: Randomized, Placebo-Controlled Trial of Green Tea Catechins for Prostate Cancer Prevention . How cool is that?

There are also studies confirming the efficiency of catechins in holding back and preventing breast cancer: Suppressive Effects of Tea Catechins on Breast Cancer: Suppressive Effects of Tea Catechins on Breast Cancer

It’s important to make a remark: neither catechins nor other substances are able to prevent the development of cancer cells. Cancer cells develop in every healthy body and the immune system is able to fight them. The problem turns up when the immune system fails and cancer cells divide faster than they are killed. Once cancer cells detected, T-lymphocytes release toxin and literally tear the cancer cell up from the inside out. Privately, I am not sure about the role of catechins in this process, and the information varies, but it seems that catechins prevent angiogenesis - the formation of new blood vessels necessary for cancer cells to grow. One way or another, today it is reliably known that the growth of cancer cells is significantly reduced by catechins. Catechins can help the body to fight cancer cells, they will prevent several cancer cells from fast growing and becoming a full tumor, able to prevent the occurrence of several types of cancer, but catechins are unable to prevent the development of a cancer cell! It should be understood, so not to fool yourself

But let's get back to fermentation. Next, we need to convert the precious catechins into theaflavine which almost of the same value!

Theaflavine moleculeа

The process of conversion of catechins into teaflavine itself is a complex process, and the proper running of all three processes, in particular, heating, fermentation and oxidation, is necessary. Therefore, during the production of dark types of tea (red, shu puer and many oolong tea) in different ways, tea is heated (roasted, steamed, smoked), oxygen and enzymes are given time to do their work, as well as favorable environment for bacteria are created (humidity, blackening, reduced blowdown). During these processes, the tea has the greatest changes in it

The interaction between tea polyphenols and enzymes (polyphenoloxazides) results in the production of teaflavine and thearubigin

Teaflavine, which is contained in tea, is an extremely interesting composition both for tealovers like you and me, and for medicine. First of all, it has a wonderful golden-red color, and second, it is teaflavine that is beneficial for our stomach. Teaflavine has antiulcer properties, and also reduces the absorption of fatty acids and cholesterol. Thus, theaflavin helps to protect our stomach from bacteria causing ulcers (Helicobacter pylori). Unfortunately, it is impossible to get rid of these bacteria as long as 80% of people have it. So why don’t we all take care of our stomach in such a simple and pleasant way as a tea party?

My friend, who is a doctor wants us to know that the Helicobacter pylori bacterium causes not only a stomach ulcer, but also duodenal ulcers, gastritis, duodenitis and gastric lymphoma. In addition, this bacterium is able to case some kinds of stomach cancer, and therefore there is every reason to believe that theaflavin helps to prevent this type of stomach cancer

This article would not be complete if I did not talk about one problem related to theaflavin. The problem is that theaflavin is a very unstable composition and, if improperly prepared (I’m looking at you, Indian tea), it turns into thearubigin. Actually, there is nothing bad in thearubigin, but there is nothing beneficial for us either. Thearubigin has dark, brown color and that is what gives dark teas its color. And it’s very important to known and understand it. The lighter, redder, more golden your brewing of red tea – the higher the quality level! If the tea producer keeps true to the technology, then the tea will have a maximum amount of theaflavins. If the producer makes tea just to sell - the tea will be too oxidized, and later - too roasted, and as a result, the compositions of theaflavin will be destroyed and more thearubigin will be produced, and therefore the brewing will turn out to be very dark. There is no use of such a tea whatsoever, although it will have a full taste

Thearubigin molecule

To see how easily theaflavin transforms into thearubigin, you can conduct an experiment that each of us has already done, accidentally forgetting a cup of tea on the table. If the cup originally was filled with good tea, with a nice brewing, an hour later it would darken and become cloudy, dark brown, and hardly transparent. There you can observe the process of oxidation of theaflavins and their subsequent transformation into thearubigins, with the corresponding color change

We can observe the disintegration of theaflavin and the formation of greater amount of thearubigin in tea. The darker the tea, the less the theaflavin and the more thearubigin it has

I think now the fact speaks for itself that light and dark teas influence our body in absolutely different ways. White and green tea help to keep the body healthy, protect us from cancer, while red tea and dark oolongs are beneficial for our stomach. Both categories of teas help to fight overweight, but in quite different ways: light teas will be useful for people who keeps the diet and want to lose weight faster, while dark teas are beneficial for people who are used to eat fatty foods and want to reduce the degree of absorption of the fats. However, I don’t want you to wait a miracle weight losing from tea. Sport and a healthy balanced diet are the best fat burners

Drink tea properly and always stay healthy!


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