Fermented tofu (furu)

Furu (腐乳) — sometimes spelled fu-ru, sufu, or dofu-ru depending on transliteration system — is Chinese fermented tofu: small cubes of firm tofu inoculated with Actinomucor or Mucor molds (occasionally Rhizopus), then brined in salt water flavored with rice wine, chili, fermented black beans, sesame oil, or other inclusions, and aged for several months. The result is a soft, almost spreadable cube with a pungent, cheese-like flavor that has earned furu the popular English nickname 'Chinese cheese.'

The production process is a two-stage mold-then-brine technique. Fresh firm tofu is cut into 2-3 cm cubes and exposed to ambient air or inoculated with a starter mold culture. Over 5-10 days at room temperature, white or grayish mold mycelium grows on the surface of each cube, developing the pehtze (the moldy tofu intermediate). The pehtze is then transferred to glass jars filled with seasoned brine (salt + rice wine + flavorings) and aged for months. The mold's proteases continue working in the brine, slowly breaking down the tofu protein into soft, soluble peptides and free amino acids — producing the soft, almost-spreadable texture and intense umami of finished furu.

Multiple regional traditions exist: bai furu (白腐乳, white furu) is the classic lightly-flavored version; hong furu (红腐乳, red furu) is colored and flavored with red yeast rice (Monascus purpureus — the same culture used for red rice wine); chou furu (臭腐乳, stinky furu) is much more strongly fermented and aromatic, a regional speciality of Hunan and Sichuan; Cantonese furu tends to be milder and used as an accompaniment to congee (rice porridge); Shaoxing furu uses Shaoxing wine in the brine. Each is editorially distinct.

Furu is used in small portions — a single 2 cm cube of furu provides the flavor of a tablespoon or two of soy sauce, with additional textural and aromatic complexity. Traditional applications include eating with morning congee (mashed onto rice), stirring into stir-fried greens (especially water spinach and bok choy), mixing into braised pork preparations, and as a condiment on the table.