Anaerobic pickled tea
The shortest dark tea route and the only one that excludes air. Air is what every other fermentation in tea depends on, and removing it changes which organisms do the work.
What makes this route what it is
Air is deliberately excluded, which no other route does. Every other microbial step in tea is managed by admitting oxygen — turning a pile, airing a warehouse — and this one is managed by keeping it out, which selects a completely different population.
The route, in order
Each note describes what the step is doing in this route. The same operation does a different job in a different chain.
Coarse mature leaf, frequently taken late in the season. The route asks for substance rather than tenderness and the material is correspondingly cheap.
Steamed or boiled. It fixes the leaf and, more importantly here, softens and part-cooks it so that it packs densely enough to exclude air in the next step.
An open, aerobic mould stage on heaped steamed leaf, used in the two-stage productions. Aerobic and mould-dominated — a different operation from the pu-erh pile it shares a record with, and the note is the record of that difference.
The single-stage productions omit it entirely and pack the boiled leaf straight into barrels, which is why they are cleaner and sharper.
Packed tight under weights and sealed beneath its own liquid. Lactic acid bacteria dominate because nothing else can, the mass acidifies, and the sourness that results is not obtainable by any other route in tea.
The two named teas take this step differently and the framing above is closer to the mainland one, which is worth saying rather than leaving for a reader to notice. The Kochi production packs the mass into wooden vats under stones, then cuts the dried block into small squares — a tea that is brewed, and usually boiled. The upland South-East Asian production packs into baskets, jars or bamboo tubes and the result is as often chewed or eaten as a preparation as it is infused, which is the older documented use in that region and is not true of the Japanese tea at all. Same operation, same organisms, two different products at the end of it.
The mass is cut into pieces or spread and sun-dried. Low temperature, in the open, which is what makes the finished tea keep.
How it differs from its neighbours
A route described on its own teaches very little. The useful fact is always which other route it is nearly identical to, and where it leaves it.
One position in the route is filled by a different named method. The shape of the route is unchanged.
The microbial slot, filled by an anaerobic bacterial process instead of an aerobic mould-and-yeast one. One word covers both in English and the two have different organisms, different conditions and unrelated results, which is the strongest argument in the catalogue for keeping the word fermentation for the cases that earn it.
Shou pu-erh
One step left outThis route leaves out an operation the other performs. Omissions are usually irreversible — the step cannot be added back later.
No rolling anywhere in the route. The leaf is never ruptured mechanically at all, which in every other family would all but ensure a mild tea and here does nothing of the kind, because the transformation is being done by organisms rather than by the leaf's own chemistry.
In full
A small family of teas across southern Japan and mainland South-East Asia is made by pickling rather than by piling. Leaf is steamed or boiled, sometimes given an open mould stage first, then packed tightly into a barrel, jar or bamboo tube, weighted, and sealed under its own liquid so that 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. It is then cut or shaped and dried in the sun. The route belongs here because it is the clearest possible demonstration that fermentation in tea is a real category with real variation inside it: piling is open, aerobic and mould-dominated, and this is closed, anaerobic and bacterial, and the two produce teas that share nothing but a word.