Douchi is a Chinese fermented soybean product. It is very similar to the Japanese hamanatto. Douchi can be made from black soybean (preferred), or soybean. One kind of douchi, sometimes called yinshi, is the dried residual black soybean koji (starter) in the manufacturing of Yinyui (pot bottom oil or pot bottom excrement, one kind of soy sauce made from black soybean, Glycine max L. merri var. o au). Good-quality douchi is made by proper control of the bean soaking and steaming processes so that the beans absorb the right amount of moisture. Usually, the moisture absorbed is less than the amount used to make soy sauce; therefore, it is harder after steaming. The manufacturing process is the same as in the manufacturing of soy sauce using black soybean.
Another kind of douchi is manufactured using a different procedure. The black soybeans are inoculated and form the koji. The koji is then washed, dripped dried, and incubated to bean temperature of 38-40°C. The beans are stacked between layers of sweetened wine with a top layer of salt. The beans are then sealed in the containers for ripening. The fermentation usually takes about a month. If the final product is too wet, they can be sun-dried to adjust the moisture content.
Douchi is a very suitable seasoning for cooking seafoods. It can eliminate the fishy flavor and at the same time provide a sweet taste. It is also used in the seasoning of meat dishes. Seasoned Douchi products with garlic, ginger, chili pepper, and/or stir-fryed in flavored oil are also now available for food preparation.
B. Manufacturing of yinshi-type Douchi or Doushi
A flowchart on douchi (yinshi) manufacturing is presented in Fig. 7 (4,6).
1. Raw Materials a. Black Soybean (Glycine max L., Merri var. o'Tau) Raw black soybean used for making douchi should be well-developed, properly dried, and free of insect damage, dirt, and other foreign material. Composition of black soybeans from different sources varies slightly (Table 2).
Table 2 Composition of Black Soybean from Taiwan (R.O.C.) and Thailand
Crude Crude Moisture Protein Fat
Foreign Ash Matters
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