Douchi is a traditional condiment for fermented bean products in China. Douchi is made by using black beans or soybeans as the main raw materials, decomposing soybean protein with Mucor, Aspergillus or bacterial protease, adding salt, wine and drying to inhibit the activity of enzymes and delay the fermentation process. There are many kinds of lobster sauce, which can be divided into black lobster sauce and yellow lobster sauce according to processing raw materials, and salty lobster sauce, light lobster sauce, dry lobster sauce and water lobster sauce according to taste.

Douchi, called "Youlong" in ancient times, is also called "addiction". The earliest record can be found in Liu Xi's Interpretation of Famous Foods in the Han Dynasty, which praised Douchi as "the sum of five flavors must exist". There is also a record of "making black beans" in the Book of Songs in the 2nd-5th century. The ancients not only used lobster sauce for seasoning, but also used it as medicine, and attached great importance to it. Han Shu, Historical Records, Qi Yaomin Shu and Compendium of Materia Medica are all recorded, and their production history can be traced back to the pre-Qin period.

According to records, the production of Douchi was first spread in Taihe County, Jiangxi Province, and then spread overseas through continuous development and improvement. The Japanese once called lobster sauce "Nachi", and later referred to sugar natto invented in Japan. Douchi is also widely eaten in Southeast Asian countries, but it is not so popular in Europe and America.