Black tea as it is known in China is actually a fermented tea, known as Hei Cha (黑茶). Unlike Western usage, where the term black tea refers to oxidized teas such as Darjeeling or Assam, in China, these teas are called red tea (Hong Cha, 红茶).
Hei Cha, on the other hand, refers to a specific category of post-fermented teas, including the famous Pu-erh (普洱茶), which is spelled Pu-erh or Pu'er tea, originating from Yunnan.
To distinguish them from red teas (Hong Cha, 红茶) – called black teas in the West – fermented teas (Hei Cha, 黑茶) are often grouped under the term "dark teas." This classification includes post-fermented teas such as Yunnan Pu-erh (普洱茶), which undergo unique aging and microbial transformation after oxidation.
A post-fermented tea is therefore a tea that has undergone a period of aging in a warm and humid environment of varying duration. A short aging period is called yellow tea, while a longer period, ranging from a few months to several years, is called dark tea.
Fermented tea may have undergone oxidation prior to fermentation and will therefore be based on black, oolong, or white tea. Then, under the influence of mold, yeast, and bacteria, it undergoes fermentation in a warm and humid environment. It may then be aged for several years, which radically changes its taste, shifting from astringency and bitterness to smoother, earthier flavors.
"Hei cha," or dark tea, is produced in many regions of China, primarily in the warmer southern provinces. It most often comes from the provinces of Sichuan, Yunnan, or Hubei. The Chinese use the term "black tea" to specifically refer to a post-fermented dark tea. Again, what Westerners commonly call "black tea" is referred to as "red tea" in Chinese. This distinct process produces a tea known as Hēichá (黑茶, literally meaning "Black Tea"), which differs from the English-language black tea known as Hóngchá (红茶, literally meaning "Red Tea") in Chinese.
See: https://lemeilleurthedechine.com/blogs/infos/le-the-ideal
The black tea production areas, the best-known and most important varieties, are located in the regions of:
Anhui: Liu an lan cha (安徽六安籃茶, Anhui Lu'an Tea Basket)
Guangxi: Liu bao cha or Six Castles Tea. (廣西六堡茶, Guangxi Liubao tea, often sold as 松黑茶, Loose leaf black 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 (Chinese tea, Tibetan tea, often called Tibetan brick tea)
Yunnan: Pu'erh cha (雲南普洱茶, either sheng pu'er "raw" 生普洱, or shu pu'er "ripened" 熟普洱)
See: https://fr.wikipedia.org/wiki/Pu-erh
It is commonly pressed into bricks or cakes for aging. Shapes also include beautiful creations such as:
Bamboo leaf logs
Cakes, or bing cha (餅茶)
Bricks, or zhuan cha (磚茶)
Loose, in baskets
Bird's nests, or tuo cha (沱茶), usually Pu'erh tea
Squares, or fang cha (方茶)
You can obtain two types of tea: raw Puerh or ripe Puerh, which differ in the way they are processed.
Once farmers have harvested, withered, cooked, rolled, and dried the raw Puerh, they press it into tea cakes of various shapes depending on their origins and traditions, and place them in a temperature- and humidity-controlled environment to age for up to decades. The fermentation process causes the tea leaves to react biologically, resulting in a dark brown color and the texture of black tea.
This results in raw dark tea or raw Puerh.
Raw Puerh can have a range of floral, vegetal, rocky, or animal flavors depending on the stage of the aging process.
Young raw Puerh has energizing properties that diminish over time during aging.
Unlike its counterpart, ripe dark tea, which undergoes double fermentation after being steeped, will contain little to no caffeine.
Production Process of Dark Pu-erh Tea (Cooked)
Ripe Pu-erh undergoes an accelerated aging process called wet-stacking, which involves spraying piles of tea leaves with water before allowing them to dry in a warm, humid environment. After several weeks, the ripe Pu-erh is pressed into tea cakes and further dried.
Characteristics of Dark Tea: The characteristics of the tea leaves are a special post-fermented tea. The aroma is aged and resembles the grassy and woody aroma of Chinese herbs. The taste is mellow and sweet, the layers and flavor are earthy, with a fuller, rounder texture.
Health Benefits of Black Tea:
It is mellow, nutrient-dense, and rich in vitamins and minerals, and is known as the "tea of life." It can aid digestion, reduce blood lipids and cholesterol, and contain antioxidants to help slow cellular aging.
Puerh is another tea highly valued for its positive health associations, such as:
Improved liver function
Anticancer properties
Improved cholesterol levels
Weight loss
Sources: https://en.wikipedia.org/wiki/Fermented_tea