Douchi

Douchi is a type of fermented and salted black soybean most popular in the cuisine of China, where they are most widely used for making black bean sauce dishes.
Douchi is made by fermenting and salting black soybeans using Qu (Chinese: 麹; pinyin: Qū), which is similar or identical to the Miso ferment, Koji. Douchi can be classified as Aspergillus-type Douchi, Mucor-type Douchi, Bacterial-type Douchi, or Rhizopus-type Douchi. There are two main stages to the Douchi making process; first you make the Koji, then there is a prefermentation stage. There can also be a maturation or post fermentation stage, were the Douchi is mixed with other ingredients, like brine, and allowed to age. The black type soybean is most commonly used. The process turns the beans soft, and mostly semi-dry (if the beans are allowed to dry). Regular soybeans (white soybeans) are also used, but this does not produce "salted black beans"; instead, these beans become brown. The smell is sharp, pungent, and spicy; the taste is salty, somewhat bitter and sweet. The product made with white soybeans is called mianchi.
Douchi, "Chinese salted black beans", and "black soybeans" are not the same as the black turtle bean, a variety of common bean that is commonly used in the cuisines of Central America, South America, and the Caribbean.
Fermented black soybeans are the oldest-known food made from soybeans. In 165 BCE, they were placed, clearly marked, in Han Tomb No. 1 at Mawangdui Tomb Site in South Central China. The tomb was sealed about 165 BCE and was first opened in 1972. The high-ranking woman to whom the undisturbed tomb belonged was probably the wife of the first Marquis of Tai.
Written in 90 BCE, the Records of the Grand Historian (aka the Shiji), by Sima Qian, Chapter 69, refers to 1,000 earthenware vessels of mold-fermented cereal grains and salty fermented soybeans (shi). They were now an important commodity in China. When the prince of Huainan (legendary inventor of tofu) was exiled for inciting rebellion (in 173 BCE) against his brother, the Han Emperor Wendi. He and his retinue were, nevertheless, provided with such necessities of life as firewood, rice, salt, shi (fermented black soybeans), and cooking utensils. This date, 173 BCE, is before Han Tomb No. 1 at Mawangdui was sealed.
It is used as an ingredient for mapo tofu. Douchi is also used to flavor fish or stir-fried vegetables (particularly bitter melon and leaf vegetables). Unlike some other fermented soybean-based foods such as natto or tempeh, douchi is used only as a seasoning, and is not meant to be consumed in large quantities, being typically much saltier.
Small packets of douchi are available wherever Chinese foods are sold.
Some common dishes made with douchi are steamed spare ribs with fermented black beans and chili pepper (豉椒排骨), and fried dace with salted black beans (豆豉鯪魚).
Fermented black soybeans are an ancient traditional food, used as condiments and seasonings in many Far Eastern countries and Chinese diaspora communities, where they are known by a variety of names.
A condiment called black bean paste, black bean sauce (豆豉醬), or black bean garlic sauce (蒜蓉豆豉酱), Tochidjan (豆豉醬), prepared from douchi, garlic, and soy sauce, is popular in Chinese cuisine.