What makes it dark tea
Dark tea is finished tea that keeps changing, through genuine microbial activity rather than the enzymatic oxidation that makes black tea black. That activity is either induced deliberately by wet-piling the leaf under heat and humidity, or allowed to proceed slowly over years of storage. Most readers arrive looking for pu-erh, which is the right word for the Yunnan teas it names and the wrong word for the category — Liu Bao is a Guangxi dark tea, Fu Zhuan a Hunan one, and neither is pu-erh.
Sheng and shou, the distinction everything else rests on
Sheng (raw) pu-erh is sun-dried leaf pressed young and left to change slowly in storage, over decades. It starts bitter, floral and astringent and softens with age. Shou (ripe) pu-erh is wet-piled at the factory for weeks, which produces a dark, smooth, earthy tea immediately. Shou was developed in the 1970s specifically to approximate in weeks what sheng takes decades to do. The two are not the same process at different speeds, and they do not taste the same at any age.
The wider category
Liu Bao from Guangxi is wet-piled by its own method and then aged in woven baskets, giving a smooth areca-nut character quite unlike shou pu-erh. Fu Zhuan from Hunan is pressed into bricks and deliberately colonised by a golden fungus whose visible specks are treated as a quality marker. Anhua dark tea includes the enormous Qian Liang logs bound in bamboo. All were historically made for the border trade and drunk boiled, often with milk and salt, rather than steeped.
Storage is production, and it is contested
For sheng pu-erh in particular, most of what determines the finished tea happens after it has been sold. Drier Hong Kong-style storage and more humid Guangdong-style storage produce recognisably different results from the same cake, and neither camp regards the other as correct. What is not contested is that badly stored tea is spoiled rather than aged, and that age alone is not quality: a mediocre cake kept twenty years is a twenty-year-old mediocre cake.
Brewing
Boiling water, a rinse discarded before the first cup, and gongfu proportions. Compressed tea needs to be broken up carefully with a pick rather than snapped, so the leaf is not shredded. Dark teas are the most generous category for a long session — fifteen infusions from good material is unremarkable — and leftover leaf is frequently boiled afterwards to extract what remains. Liu Bao and Fu Zhuan take simmering particularly well.
Common misconceptions
That pu-erh and dark tea are synonyms. That the microbial change is the same thing as oxidation — popular writing calls both 'fermentation', which is why so many readers believe pu-erh and black tea are made the same way. That all dark tea is low in caffeine, for which the evidence is not strong and where brewing style matters far more. And that older is automatically better, which is a marketing convenience rather than a rule.