Sufu (豆腐乳) is fermented or preserved tofu. Its name is Ningbo dialect for Mandarin doufuru. Sufu literally translates as either "bean-rotten-milk" or "spoiled tofu" and it is known as "furu" in China, "tahuri" in the Philippines, "chao" in Vietnam, and as "taokoan" or "takoa" in Indonesia. Sometimes it is sold as "Chinese cheese" in Western countries, and in Singapore it is commonly known as "stinky tofu".
This type of soybean curd is made by cutting tofu up into smallish chunks, steaming or lightly boiling them, and then inoculating them with the spores of edible fungus. The fungal species normally used are Actinomucor elegans, Mucor racemosus, or any of many members of the genus Rhizopus, particularly Rhizopus oligosporus, which is normally used to make tempeh. These fungi all produce antibacterial substances which greatly aid in preserving the curd.
The curd is then skewered on bamboo, salted, and fermented for 3-7 days in a covered box at about 30°C. Then, the curd is taken off the skewers and put in jars with a salt-alcohol brine. Rice wine is often used, and the preserving solution is 9-25% salt and 2-10% alcohol. Sometimes spices such as capsicum peppers, bay, star anise, and sesame oil are added to the brine. The sufu is aged in this brine for anywhere from a few months to a few years.
The resulting product is very soft and creamy, and the short-chain amino acids in it are supposedly very digestible.
Sufu comes in red and white varieties. The red type is colored with a rice-based powder that has been fermented with the fungus Monascus purpureus.
The more sufu has aged, the more pungent it gets. It is often served mixed with meat or vegetables and flavored with garlic or chili peppers. A common Chinese breakfast is sufu mixed with rice.
Big thanks to gn0sis for the Chinese characters and some of the translation information!