Metabolism of tea trees

In this section, I would like to introduce an interesting point of view on the substances contained in tea from trees of different age and in regards to their metabolism. It was originally written by Chinese author Isundust at the www. puer.cn website. I must admit that the author possesses ample knowledge of tea trees and their functioning. In regards to tea plant cultivation, he is emphasizing factors influencing the growth such as shading, temperature, watering, soil composition, use of fertilizers, orientation, and altitude. Then he points out that as the food absorption and the metabolism is changing in humans with the age (for example that of youngsters is vigorous and that of old people is slow), the same may apply to plants, just in a different manner, and therefore substances contained in tea leaves are changing through the absorption and metabolism of the tea plant with its age.

Tea trees aged 0-30 years have relatively vigorous nitrogen metabolism and produce a large amount of nitrogen-related products such as amino acids, proteins, tea polyphenols, etc. Therefore, tea trees that are young are fresher but less sweet.

Trees over 30 years old have obvious carbon metabolism and produce large amounts of monosaccharides (such as glucose, fructose, ribose, etc.), oligosaccharides (such as maltose, sucrose, raffinose, etc.), and polysaccharides (glycogen, starch, chitin), hyaluronic acid, hemicellulose, etc.), glycoproteins, proteoglycans and glycolipids. Therefore, the bitterness in the tea leaves is low, and the sweetness and mellowness are good.
Generally speaking, carbon metabolism and sweetness are becoming more obvious with the growing age. Since the post-fermentation of raw Pu’er tea is closely related to the sugar content of tea leaves, mature buds and older tea tree buds will age better, so some people prefer ancient tree tea and big tree tea. In fact, for tea trees over 30 years old, if the ecological environment is not bad and the number of pickings is small, then it is more difficult to distinguish trees of 30 and 50 years, and trees of 70 to 80 years.

The biochemical difference between plantation bushes, small trees, old trees, ancient trees, big trees, and thousand years old wild tea trees is that they have different metabolisms. Nitrogen metabolism is obvious when trees are young, and carbon metabolism is obvious when trees are old.
According the taste of tea, Isundust prefers raw sheng Pu’er tea with a sense of sweetness gained with ageing years. The first sweetness is interlinked with the age of the tree, and the second is the sweetness brought by the ageing process. For ordinary consumers, the taste of eco-tea trees of 30 years is already very good.

Isundust is also suggesting an unorthodox method of steeping tea and observation of the sweetness of tea infusions:
Pick three grams of tea from the same tea area, the same variety, the same quality of leaves, the same season and steep in 250 ml fresh boiling water for five minutes. Drink it when it gets cold, the good sweetness will be more obvious in the tea from older trees. Because the fructose contained in the tea leaves increases the sweetness of tea infusion at lower temperatures, it will then gradually increase the sweetness of infusion at temperatures below 40°C and decrease the sweetness of infusion above 40°C.4

Here I have a bit mingled understanding of what the author want to say about the “same” tea area etc. It seems like he is making a comparison between two ways of preparing tea – the hot and cold version. However, later he is describing the infusion after “it gets cold”, so I need to make my own observation of this technique and come with conclusion.
Or may “you the reader” write your opinion that?

The origin of tea trees

Imagine the forest some thousand years ago. How many trees could have possibly survived till now, even the human exploitation?
Yet, I will tell you that there are still trees, which were yielding the harvest of tea leaves to dozens and maybe even a hundred of generations back. The place of origin of the chashu 茶树 / the tea plant or Camellia sinensis is in the Yunnan province of China. The same place where I decided to spend my one-year scholarship during my studies at university in 2007. Yunnan deeply stroke my heart. It is one of the most beautiful, adoring and most uneasy place to explore.
There are still over a hundred and over a thousand years old tea trees growing in this area. However, trees are not bound only to one exact region. Their population are exceeding far beyond any political border, and today, we can find them in Vietnam, in Laos as well as in Burma.  Throughout thousands of years have these trees evolved into different colonies with different features. Some have leaves covered by tiny hair, some don’t, some are very bitter, some are sweet. And all can be produced into the most delicate beverage – tea.
But let’s get back to China, as it is the cradle of tea and peak a bit into the history. As early as 3000 years ago, the wild tea collected from the virgin forest in southern Yunnan became a tribute to the Zhou Dynasty. Since then, through the Qin, Han, Tang, Song, Yuan, Ming, and Qing Dynasties, tea in southern Yunnan not only became a tribute to the imperial court but also became an important material to exchange horses from Western Asia through barter trade. For thousands of years, southern Yunnan has been transported by caravan, exchanging tea for horses and trading tea. At the end of the Ming Dynasty and the beginning of the Qing Dynasty, Simao city built an “official road” from Pu’er city to Kunming city, the provincial capital, for the convenience of paying “Pu’er tea” to the capital. This Caravan Road, which goes north and south, east and west, is the ancient tea horse road which was later called “Southern Silk Road” internationally. The ancient tea horse road extends outward through the sea passage to America, Europe, Africa, and Oceania. 1

 On my journeys throughout China and particularly Yunnan province (each spring from 2012 to 2019, except 2014), I have come across places with above hundred years old tea trees in the Xishuangbanna region, as well as a thousand and above years old tea trees in Baoshan and Lincang region. The oldest tea tree is called Xiangzhuqing 香竹箐. But this one is of a different species then Camellia sinensis. According to Chinese research made in 2010, this tea tree is 3200 years old and belongs to the wild species called Camellia Taliensis (bearing the name of Dali town). This tree is also addressed as chazu 茶祖 the “tea ancestor”. This wild species of thousand years old tea trees with big trunk and high crown can be found all along the Lancang River in Baoshan and Lincang region. The common mark of its leaves is glossy texture without much hair and with quick oxidative properties, which is very suitable to produce Yesheng hongcha 野生红茶 – wild black tea. Some producers, however, produce also green Pu’er tea from its leaves, which can be of a very nice flowery taste, but much different to all Pu’er from big leaf variety. Local people in Mangshui town have another name for it – the Datang Hongku 大塘·红裤 – the “Red trousers from Big dike”. 

But let’s take it from the very bottom. All tea varieties can be divided into generative varieties (“有性系” you xingxi / sexual) spreading naturally by seeds, and vegetative varieties (“无性系” wu xingxi / asexual) spreading by cuttings. Generative varieties are also known as  “群体种” qunti zhong which means colony/group variety. Then almost all big tea trees in Yunnan are addresed as the Big leaf variety 大叶茶品种 daye cha pinzhong in Chinese and in Latin it is known as Camellia sinensis var. Assamica. These big leaf trees are divided into three varieties bearing the names of their places of origin: 凤庆种 Fengqing variety 勐库种Mengku variety, 勐海种 Menghai variety. These varieties differ in their trunk measurements, the height of the tree, the type of the tree crown, the shape and color of its leaves, which are most suitable to produce Pu’er tea 普洱茶 and hongcha 红茶 – we know it as black tea.2 Other group of trees are wild tea tree varieties which is commonly addressed as Yesheng chashu qunluo 野生茶树群落.

Speaking of old tea trees, it does not merely mean the old age of the tea tree, but also that the tree has deep roots with strong vitality to absorb sufficient nutrients. That can be reflected as a richness of substances in the tea. If we make a comparison of two teas from the same environment, tea from ancient trees would be more complex with longer lasting then the tea from small tea bushes.

From the age perspective, tea trees in Yunnan province can be divided into these categories

  1.  “千年野生古茶树 Qiannian yesheng gu chashu”
    Thousand-years wild tea trees (before and around the Tang Dynasty 618-907, over 1,000 years old)
  2. “大茶树 Da chashu” Big tea tree (500~1000 years old trees in Song Dynasty/ 960–1279)
  3. “原生态 古茶树 Yuan shengtai gu cha shu”
    Native ecological ancient tea tree (300~500 years old tea trees cultivated around Ming Dynasty / 1368 – 1644)
  4. “生态古茶树 Shengtai gu cha shu” or ecological”  ancient trees  (100-200 years old trees, Qing dynasty 1644 – 1911)
  5. 老茶树 Lao chashu Old tea trees (60-100 years old trees, Republic of China 1912-1949)
  6. 小茶树 Xiao chashu Small tea trees (35-60 years old trees, PRC 1949-1976)
  7. 台地茶树 Taidi chashu Plantation tea trees (After 1976 up Today 0-35 years)  

Sources: 
1. chinese book 解密软黄金 | 普洱茶品鉴;
2. chinese book茶源地理 临沧 吴垠/主编 文/杨钰鸾手绘/袁潮燊
3. www.360doc.com/content/15/0204/23/16921388_446334007.shtml