Anaerobic pickling
Packing steamed leaf into a sealed vessel and excluding air, so lactic acid bacteria rather than moulds carry out the fermentation.
The categories this step defines
In tea, processing is not a modifier applied to a category — it is what creates the category. These are the types that exist because this step exists.
- Dark tea and pu-erh — Post-fermentation: microbial wet-piling (shou) or extended natural ageing (sheng).
What it is
A small family of teas across southern Japan and mainland South-East Asia is made by pickling rather than by piling, and it is the clearest demonstration in tea that fermentation is a real category and not a loose synonym for oxidation. Leaf is steamed or boiled, packed tightly into a barrel, jar or bamboo tube, weighted, and sealed under its own liquid so oxygen is excluded. Under those conditions lactic acid bacteria dominate, the mass acidifies, and the finished tea is distinctly sour — a taste no other tea process produces. Kochi’s goishicha runs an aerobic mould stage first and an anaerobic barrel stage second; Tokushima’s awa bancha uses the anaerobic stage alone; Thai miang and Burmese laphet are pickled to be eaten as much as infused, which is the older use across the region.
Also transliterated as: tsukekomi, goishicha, miang.
What it does to the leaf
Excludes oxygen from a mass of heat-treated leaf so that lactic acid bacteria dominate the microbial population, acidifying the leaf and transforming it under anaerobic conditions.
What it does to the cup
Produces a pronounced sourness with a light, clean body; goishicha and awa bancha brew thin, pale and tart in a way that reads as unlike tea to most first-time drinkers.
Variants that matter
Ways this step is carried out that produce genuinely different results, rather than regional names for the same thing.
- Two-stage (goishicha)
- An aerobic mould fermentation on heaped steamed leaf, followed by an anaerobic barrel stage, then cutting into squares and sun-drying.
- Single-stage (awa bancha)
- Boiled and rubbed leaf packed straight into barrels under weights, with no mould stage at all.
- Eaten rather than brewed (miang, laphet)
- Pickled tea leaf served as a food, which is documented as the older pattern across upland South-East Asia and remains current.
Where this gets misdescribed
These teas are frequently filed as unusual dark teas made like pu-erh. The microbiology is the other way round: pu-erh piling is an open, aerobic, mould- and yeast-dominated process, while these are closed, anaerobic and bacterial. They are also the reason the word fermentation cannot simply be abandoned in tea writing — here it is precisely the right word, which is why it has to be reserved for the cases that earn it.
Other steps at the Fermentation stage
- Fungal flowering (jin hua) — Deliberately cultivating Eurotium cristatum on compressed dark tea until visible golden spores develop.
- Liu Bao pile fermentation — Wuzhou’s own microbial piling process for Liu Bao, which shares a family with pu-erh wet-piling and is not the same operation.
- Turning the pile (fan dui) — The scheduled turns that redistribute a fermenting heap, which is how a pile is steered — the temperature at its core is the whole control system.
- Wet piling (wo dui) — Deliberate microbial fermentation of finished leaf under heat and humidity — what makes shou pu-erh.
- Wetting the pile (chao shui) — The measured addition of water to dry maocha that starts a wet-piling fermentation, and the single decision that most determines what the finished shou tastes like.
Teas that go through this step
Guides covering this step
- Three different changes, one misused word — Oxidation, yellowing and microbial fermentation are three unrelated processes that English-language tea writing routinely calls by the same name. Separating them is not pedantry — it is what makes half the category descriptions in tea stop contradicting each other.
Sources
- TeaHQ editorial synthesis — TeaHQ
This page is TeaHQ’s own synthesis of well-attested production practice. No external technical document stands behind it, so it describes what producers do rather than asserting measured process parameters.
Written comparisons
Where TeaHQ has set this step against something it is routinely confused with, and argued the differences out in full.
- Anaerobic pickling vs wet piling — The fermentation behind laphet and miang against the fermentation behind shou pu-erh. One excludes air so that lactic acid bacteria dominate; the other admits it so that a mixed aerobic population works through a heap. They are opposite designs and they produce opposite results.