Fermented black beans, also called salted black beans or douchi, are whole black soybeans fermented and dried to a deep black color, used as a pungent, salty-savory seasoning in Chinese cooking. Douchi dates back to at least the Han dynasty (206 BC-220 AD) in China, where it was used as a seasoning and condiment.
Today they come mainly from southern China (Guangdong, Guangxi, Sichuan) and are used across Chinese, Vietnamese, Thai, and Korean cooking as a base for stir-fries, braises, marinades, and dipping sauces, most famously in Cantonese black bean sauce. Rinse or briefly soak the beans before use to soften their intense saltiness, then pair with garlic, ginger, and chili, which balance their deep, almost cheese-like fermented flavor.