Chapter 3 · 7 / 8
Dietary Fibre and the World the Microbes Make
Body, viscosity and roundness. The dietary fibre that shapes texture rather than taste or aroma, and the microbial metabolism at work in post-fermented teas such as pu-erh.
The lessons are narrated in Japanese.
How to turn on English subtitles
- Start the video and click the CC button to switch captions on.
- Open Settings (the gear icon) → Subtitles/CC → Auto-translate.
- Choose English.
These are machine-translated from the Japanese captions, so expect some roughness — particularly around tea terminology. The text on this page is a proper translation, so read the two together.
So far we have concentrated on the compounds behind the flavour of tea. But the appeal of tea is not only taste and aroma.
There is also a large role played by the compounds that shape texture — body, viscosity, roundness in the mouth. The lead here belongs to dietary fibre and to the metabolic products of microorganisms.
Dietary fibre divides broadly into the soluble and the insoluble.
- Soluble fibre (pectin, for example) gives tea viscosity and body, and forms a rich mouthfeel. Pectin is broken down by the action of microorganisms, making the taste more complex still.
- Insoluble fibre (cellulose, lignin) is the main constituent of the cell walls of the leaf. These extract poorly; lignin in particular, abundant in stems and hardened leaf, can at times be a source of bitterness and harshness.
In some teas — especially ripe pu-erh and post-fermented dark teas such as Awa bancha — particular microorganisms, moulds and bacteria, are put actively to work during manufacture. These organisms break down and convert the constituents of the leaf through fermentation, producing distinctive flavours and possible health properties.
The microbes “cook” the leaf in something like the following ways.
- Breaking down pectin (soluble fibre) → producing organic acids such as succinic acid, adding sourness and a complex body.
- Breaking down cellulose (insoluble fibre) → generating a faint sweetness.
- Converting catechins → softening astringency and rounding the taste.
- Breaking down proteins and lipids → forming umami and distinctive aromas.
Drinking a post-fermented tea, then, is a matter of enjoying not only the constituents of the leaf itself but the varied metabolites produced by microbial action.
Some of the compounds arising during microbial fermentation are being studied for their relationship with the gut environment.
- Exopolysaccharides (EPS) are a kind of dietary fibre produced by microorganisms. They are of interest as prebiotics — food for beneficial bacteria in the gut — and may contribute indirectly to a healthier gut environment.
- Lipopolysaccharides (LPS) are a component of the cell walls of some microorganisms. Taken orally in very small quantities, they have been suggested to stimulate gut immune function gently and help keep it in balance.
Their action is complex, and this is a field where research still has some way to go.
Post-fermented teas involving microorganisms are particularly distinctive in texture, but every tea has a quality of its own: the clean finish of green tea, the firm body of black tea, the soft mouthfeel of white tea. Texture also changes with the region, the method of manufacture and the way it is brewed.
We hope that knowing something of what lies behind these compounds lets you enjoy the taste of tea more deeply, and in more dimensions.