Douchi also called Chinese fermented black beans , is a flavoring most popular in the cuisine of China, and is used to make black bean sauce.

Douchi is made by fermenting

Fermentation (food)

Fermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. Fermentation in simple terms is the chemical conversion of sugars into ethanol...

 and salting soybean

Soybean

The soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...

s. The process turns the beans black, soft, and mostly dry. The flavor is sharp, pungent, and spicy in smell, with a taste that is salty and somewhat bitter and sweet.

Douchi should not be confused with black turtle beans, a variety of common bean

Common bean

Phaseolus vulgaris, the common bean, is an herbaceous annual plant domesticated independently in ancient Mesoamerica and the Andes, and now grown worldwide for its edible bean, popular both dry and as a green bean. The leaf is occasionally used as a leaf vegetable, and the straw is used for fodder...

 that is commonly used in the cuisines of Central America, South America, and the Caribbean.

In Japanese

Japanese language

is a language spoken by over 130 million people in Japan and in Japanese emigrant communities. It is a member of the Japonic language family, which has a number of proposed relationships with other languages, none of which has gained wide acceptance among historical linguists .Japanese is an...

, douchi is also referred to by the same kanji

Kanji

Kanji are the adopted logographic Chinese characters hanzi that are used in the modern Japanese writing system along with hiragana , katakana , Indo Arabic numerals, and the occasional use of the Latin alphabet...

 (豆豉) and pronounced as touchi.

The process and product are similar to ogiri

Ogiri

Ogiri is a flavoring made of fermented oil seeds, such as sesame seeds or egusi seeds. The process and product are similar to iru or douchi. Its smell is like cheese, miso, or stinky tofu.Ogiri is best known in West Africa....

and iru, both being African fermented bean products.

In Vietnam

Vietnam

Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...

, this sauce is called tàu xì or đậu xị and is made from black bean.
Douchi is especially used to flavor fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 or stir-fried

Stir frying

Stir frying is an umbrella term used to describe two Chinese cooking techniques for preparing food in a wok: chǎo and bào . The term stir-fry was introduced into the English language by Buwei Yang Chao, in her book How to Cook and Eat in Chinese, to describe the chǎo technique...

 vegetables (particularly bitter melon

Bitter melon

Momordica charantia, called bitter melon or bitter gourd in English, is a tropical and subtropical vine of the family Cucurbitaceae, widely grown in Asia, Africa, and the Caribbean for its edible fruit, which is among the most bitter of all fruits...

 and leaf vegetable

Leaf vegetable

Leaf vegetables, also called potherbs, green vegetables, greens, leafy greens or salad greens, are plant leaves eaten as a vegetable, sometimes accompanied by tender petioles and shoots...

s).