Post-fermented tea

Post-fermented teas are a class of teas that have undergone a period of "aging" in open air, from several months to many years. The exposure of the tea to microflora, humidity and oxygen in the air causes it to undergo further oxidation through auto-oxidation, fermentation, and possibly some reactivated oxidative enzymes in the tea. This alters the smell of the tea and typically mellows its taste, turning previously astringent or bitter teas into products that are thick and unctous, with pleasant mouth-feels and aftertastes. In Chinese and Chinese-influenced East Asian cultures, post-fermented teas are collectively referred to as "Dark tea" or "Black tea" (黑茶, hēi chá) due to the dark brown infused liquors from this class of teas. This should not be confused with the "Black tea" commonly referred in Western culture, which in East Asian cultures is called "red tea."

Types

The best known of the post-fermented tea class is "Pu-erh tea"; however, there are several other types of teas that are also of this class, including:
*"Pu-erh tea" (雲南普洱茶, yúnnán pǔ'ěr chá)
*"Liu'an tea" (安徽六安籃茶, ānhùi lìu'ān lán chá)
*"Liubao tea" (廣西六堡茶, guǎnxī lìubǎo chá)
*"Hunan dark tea" (湖南黑茶, húnán hēi chá)
*"Laobian tea" (湖北佬扁茶, húběi lǎobiǎn chá)
*"Bian tea" (四川邊茶, sìchuān biān chá)

Production

Many post-fermented teas do not arrive on the market as "finished" products, instead they often start off as green teas or partially-oxidized oolong-like teas, which are then allowed to slowly oxidize and undergo microbial fermentation over many years, thus turning into post-fermented tea. Alternatively, post-fermented teas can be created quickly through a ripening process spanning several months, as seen in "ripened pu-erh". This ripening is done through a controlled process similar to composting, where both the moisture and temperature of the tea are carefully monitored. The resulting product from this fermentation is "finished" post-fermented tea.

Teas destined to be consumed as post-fermented teas are commonly sold as compressed tea of various shapes, including bricks, discs, bowls, or mushrooms. Ripened pu-erh are ripened in loose form prior to compression. Post-fermented teas can be aged for many years to improve their flavor. In the case of raw pu-erh tea, it can be aged up to 30 to 50 years without diminishing in quality, and ripened pu-erh can be aged up to 10 to 15 years. However, experts and aficionados disagree about the optimal age to stop the aging process.

Many Tibetans and Central asians use pu-erh or other post-fermented teas as a caloric food, boiled with yak butter, sugar and salt to make yak butter tea.