Fermented tea

Fermented tea (also known as post-fermented tea or dark tea) is a class of

The fermentation of tea leaves alters their chemistry, affecting the organoleptic qualities of the tea made from them. Fermentation affects the smell of the tea and typically mellows its taste, reducing astringency and bitterness while improving mouthfeel and aftertaste. The microbes may also produce metabolites with health benefits.^[1][3] Additionally, substances like ethyl carbamate (urethane) may be produced.^[4]

The fermentation is carried out primarily by molds. Aspergillus niger was implicated as the main microbial organism in the pu'er process,^[1][5][6] but that species identification has been challenged by comprehensive PCR-DGGE analysis, which points to Aspergillus luchuensis as the primary agent of fermentation.^{[7][8][9][10]}

Most varieties of fermented teas are produced in China, its country of origin, with several varieties also produced in Korea^[11] and Japan.^[12] In Myanmar, lahpet is a form of fermented tea that is eaten as a vegetable, and similar pickled teas are also eaten or chewed in northern Thailand and southern Yunnan.^[13]

The early history of dark tea is unclear, but there are several legends and some credible theories.

For example, one legend holds that dark tea was first produced accidentally, on the

Other historical accounts attribute the first production of dark tea to the Ming dynasty in the 15th and 16th centuries. It may have been first traded by tea merchants much earlier than the legends state, across the historical borders of Han and Tibetan cultural areas.^[15]

Fermented teas can be divided according to how they are produced. Piled teas, such as the Chinese post-fermented teas, and the Toyama kurocha produced in Japan, are fermented with naturally occurring fungus under relatively dry conditions. Other fermented teas, called pickled teas, are fermented in a wet process with lactic acid bacteria. Pickled teas include miang from Thailand and awabancha from Japan.^[16] A third category, including the Japanese goishicha and Ishizuchi kurocha, is fermented with the piled and pickling methods successively.^[17]

Fermented tea originated in China, where it is commonly known as hei cha (黑茶) or dark tea. Hei cha is produced in many areas of China, mostly in the warmer southern provinces. It is commonly pressed into bricks or cakes for ageing.^[1][2]

The most famous and important producing areas and varieties include:

• Anhui: Liu an lan cha (安徽六安籃茶, Anhui Lu'an basket tea)
• Guangxi: Liu bao cha (廣西六堡茶, Guangxi Liubao tea, often sold as 松黑茶, loose dark tea)
• Hubei: Qing zhuan cha (湖北青砖茶, Hubei green brick tea)
• Hunan: Fu zhuan cha (湖南茯磚茶 (黑茶), the famous fu zhuan 茯磚茶 “brick tea”)
• Jingyang, Shaanxi
  : Fu zhuan cha (陕西泾阳茯茶 (黑茶), the famous fu zhuan 茯磚茶 “brick tea”)
• Sichuan: Lu bian cha (四川路边茶, Sichuan border tea)
• Tibet: Zang cha (藏茶, Tibetan tea, often called Tibetan brick tea)
• Yunnan: Pu'er cha (雲南普洱茶, either "raw" sheng pu'er 生普洱 or "ripened" shu pu'er 熟普洱)

Shapes include:

• Bamboo leaf logs
• Cakes, or bing cha (餅茶)
• Bricks, or zhuan cha (磚茶)
• Loose, in baskets
• Bird nests, or tuo cha (沱茶), usually pu'er tea
• Squares, or fang cha (方茶)

Several distinct varieties of fermented tea are produced in Japan.

Many Tibetans and Central Asians use pu'er or other fermented teas as a caloric and micronutrient food, boiled with yak butter, sugar and salt to make yak butter tea.

Post-fermented tea usually gets more valuable with age. Dark tea is often aged in bamboo baskets, bamboo-leaf coverings, or in its original packaging.

Many varieties of dark tea are purposely aged in humid environments to promote the growth of certain fungi, often called "golden flowers" or jin hua (金花) because of the bright yellow color.^[37][38]

• List of Chinese teas
• Kombucha, a beverage produced by fermentation of brewed tea using a symbiotic culture of bacteria and yeast