Doubanjiang (豆瓣酱, “broad bean paste”) is the fermented chili bean paste behind mapo tofu, twice-cooked pork and fish-fragrant dishes. The famous kind comes from Pixian, now part of Chengdu: broad beans (fava beans) are made into a koji, fermented in brine, and mixed with salted, chopped red chilies, then aged in open vats that are stirred and sunned for months or years until the paste turns dark red-brown, savory and deep. Plain (non-spicy) broad bean pastes exist too, but in Sichuan cooking “doubanjiang” usually means the chili version.
How It Ferments
The first stage is a koji: cooked broad beans mixed with flour are grown over with Aspergillus oryzae, the mold used for miso and soy sauce, whose enzymes break proteins into savory amino acids and starch into sugars. The koji is then mixed with salt water to make a fermented bean mash; in studies of broad bean koji, almost only Aspergillus was left by the end of the koji stage (Li et al., 2023). As the bean mash and salted chilies age together, salt-tolerant bacteria and yeasts take over – Bacillus, Staphylococcus, Tetragenococcus and yeasts such as Zygosaccharomyces – and the chili variety and length of aging shape its acids, amino acids and aroma (Yang et al., 2022; Liao et al., 2026). Traditional open-air sunning isn’t just folklore: paste fermented in sunlight developed more fruity, floral and roasted aromas than paste kept in the dark (Zhao et al., 2022).
Why the Salt Level Matters
Doubanjiang is very salty, and that’s part of what keeps it safe. When researchers fermented it at 12%, 9% and 6% salt, the low-salt version acidified faster but built up excessive biogenic amines – compounds such as histamine that can cause headaches, flushing and other reactions – at about 1,457 mg per kg (Liao et al., 2026). That’s why our home recipe keeps the paste at about 12% salt by weight. Use it as a seasoning – a tablespoon flavors a whole dish – and leave out other salt.
Safety: Molds and What You Buy
- Use a known koji mold. Aflatoxin B1, a potent liver toxin made by molds such as Aspergillus flavus, is a standard monitoring test for Pixian doubanjiang (Zeng et al., 2022). At home, inoculate your beans with bought Aspergillus oryzae spores (koji-kin) rather than waiting for wild molds. Harvest the koji while it’s white to pale yellow, before it turns green with spores, and discard the whole batch if black, pink or olive patches appear – don’t cut them away. Aflatoxin-producing molds look much like koji, which is why the bought spores matter.
- Buy from reputable brands. In 406 retail samples of Pixian doubanjiang, chromium exceeded limits in 9.4%, and non-branded pastes had higher levels of lead, mercury, cadmium and arsenic, and more histamine, than branded ones (Wen et al., 2026).
- Live cultures: store-bought doubanjiang is usually cooked into food anyway, so treat it as a seasoning, not a probiotic.
Cooking With It
Fry doubanjiang gently in oil until the oil turns red and fragrant before adding other ingredients – that’s the base of mapo tofu, twice-cooked pork and many Sichuan braises. Chop it finer for sauces. Compare it with Korea’s gochujang and doenjang, Japanese miso, and Sichuan’s other ferment, pao cai. China’s red-mould rice is hong qu.