What is Pu-erh Tea? Part 3 - The science of tea fermentation

by Niraj Lama April 09, 2019 0 Comments

In this third part of our series on Pu-erh tea we look into the fermentation in pu-erh tea a little closely and the changes it brings about in post-fermented teas.  

Fermentation and Recipes

So what exactly causes the tea to ferment in pu-erh and what does that process do to the tea? We are often times asked this question. Also the question how kombucha is different than pu-erh often arises because kombucha is also a fermented form of tea.

What is Pu erh Tea?

The fermentation in pu-erh is initiated when the tea is steamed and compacted. Microorganisms start growing in the tea leaves due to the moisture trapped in the cake. These bacteria and fungi react with the chemicals in the tea, producing different flavors while also changing the chemical composition of the tea.

Ripe Menghai Puerh

The fermentation that undergoes in the pu-erh tea is "solid state fermentation," as opposed to kombucha where the fermentation happens in a liquid triggered off by a symbiotic culture of bacteria and yeast (SCOBY). Aspergillus niger, a fungus, is the predominant microbe found in both sheng and shu pu erh. Aspergillus niger is considered to be a "industrial fungus" because it is also cultured to produce substances like citric acid, gluconic acid, high-fructose corn syrup, and pectinases. The latter is used for cider and wine clarification.

Pu erh ripe microbes

While Aspergillus niger is relatively found more in shu pu-erh, research has uncovered in sheng pu-erh a yet underdetermined species of Aspergillus fungus in higher concentration. Other microbial members included Penicillium, Rhizopus, Saccharomyces, Actinoplane, Streptomyces and Bacterium.

The 2016 study "The Microbiome and Metabolites in Fermented Pu-erh Tea as Revealed by High-Throughput Sequencing and Quantitative Multiplex Metabolite Analysis "* also had some interesting findings:

  • Fungal diversity is higher in fresh tea leaves than in pu-erh, while bacterial presence is more in pu-erh than in fresh tea leaves.
  •  More bacterial diversity in sheng pu-erh than shu.
  • Aged sheng has the same amount of fungal and bacterial community as a new shu pu-erh. (The researchers were comparing a 28 year old sheng).
  • The microbial community does not change much between a new and an old shu. Which means shu pu-erh may not necessarily benefit from aging.
  • Some of the microbes found in pu-erh are potentially toxic although the toxins themselves were not found in prepared tea. It is advisable to rinse the tea once before using it.

Pu erh soup microbes

Traditionally, pu-erh specially the ripe variety is thought to be very good for digestion. People in Asia, where pu-erh is popular, often drink shu with rich food like dumplings. Also pu-erh fans  believe that both varieties of the tea impart a benefit at a more psychic level - triggering off a "qi" effect, where a warm fuzzy sensation can be felt in various parts of your body. Some describe it as a kind of a high.

Another scientific study identified statins, popular medicine against coronary diseases, in pu-erh.

Pu-erh Recipes

Pu-erh cakes come with a number printed on their wrapper. This number which is consists of 4 digits is called the "recipe." The first two numbers indicate the year, the third number leaf grade and the last number denotes the factory where it came from. For example our 2006 Feng Qing Raw Pu-erh Tea comes with recipe number 7813. This means the first production of this recipe took place in 1978. The grade of leaf used is 1 and it comes from factory number 3 or Xiaguan Tea Factory.

2006 Feng Qing Bing Cha

The most famous and sought after recipe number is 7542. A blend that started in 1975, with grade 4 leaves and made by factory number 2, which is Menghai tea factory.

There are 10 and more grades of leaf for making pu-erh. Although the higher grade means more larger and broken leaves, it is not a consistent system and does not reflect on the quality of the tea.

As for the factory and its corresponding numbers they run as below.

  1. Kunming Tea Factory
  2. Menghai Tea Factory
  3. Xiaguan Tea Factory
  4. Lan Cang Tea Factory or Feng Qing Tea Factory
  5. Pu-erh Tea Factory
  6. Six Famous Tea Mountain Factory
  7. Unknown/not specified
  8. Haiwan Tea Factory and Long Shen Tea Factory

*The Microbiome and Metabolites in Fermented Pu-erh Tea as Revealed by High-Throughput Sequencing and Quantitative Multiplex Metabolite Analysis. - Yongjie Zhang, Ida Skaar, Michael Sulyok, Xingzhong Liu, Mingyong Rao,and John W. Taylor

**Effect of microbial fermentation on content of statin, GABA, and polyphenols in Pu-Erh tea. - Jeng KC1, Chen CS, Fang YP, Hou RC, Chen YS.    

What is Pu-erh Tea? Part 1Part 2, Part 4

Niraj Lama
Niraj Lama


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