If you’ve ever cooked Mapo Tofu, Sichuan hot pot, or fiery stir-fried dishes, you’ve tasted the soul of Sichuan cuisine: doubanjiang (豆瓣酱). This iconic fermented broad bean and chili paste brings layers of umami, heat, and tang that no other condiment can replicate. While the traditional process comes from the city of Pixian, Sichuan, today I’ll walk you through an adapted homemade method designed for avid fermenters in the West.

📜 A Brief History of Doubanjiang 豆瓣酱

Originating in Pixian County, Sichuan, doubanjiang is often called the “soul of Sichuan cooking”.
Traditionally, it’s made with erjingtao chilies, broad beans, salt, and long fermentation under the Sichuan sun.
The paste ferments for months (often years) in clay crocks, developing its signature red color and complex aroma.
It’s the foundation of dishes like Mapo Tofu, Twice-Cooked Pork, Sichuan hot pot, and even simple stir-fried greens.

🧄 Flavor Profile

Homemade doubanjiang is a flavor bomb:

Savory umami from broad beans and koji fermentation.
Fruity heat from red peppers.
Spice and perfume from Sichuan peppercorn, star anise, and cloves.
Tangy funk from months of natural fermentation.

It’s salty, spicy, slightly sour, and deeply complex—one spoonful transforms a dish.

🌶️ How to Make Doubanjiang

Fermented Broad Beans (Broad Bean Koji)

300 g dried broad beans
0.3 g Aspergillus oryzae (koji spores), mixed with 3 g rice flour
1000 g fresh red pepper
Kosher salt
Water

Peppers

1000 g fresh red peppers (I used red jalapeños as a substitute for hard-to-find erjingtao chilies)
100–200 g dried Chinese chilies (like Tianjin)
Kosher salt

Spices

2 star anises
3 bay leaves
1 tbsp red Sichuan peppercorn
1 small piece cinnamon
¼ tsp cloves
¼ tsp fennel seeds
2 cardamom pods

Other

Neutral oil (avocado, canola, or grapeseed)

🔬 Koji & Fermentation: The Science Bit

The secret to doubanjiang’s complexity is koji—the same mold used for miso and soy sauce. You can buy koji spores online from fermentation suppliers.

To grow koji:

Broad beans are soaked, steamed, and inoculated with spores.
They ferment at about 30 °C and 70–75% relative humidity for 48 hours.
A fuzz of mold forms, breaking down starches and proteins into sugars and amino acids (umami!).

⚙️ My hack: I use an old fridge retrofitted with a space heater, humidifier, and Inkbird controllers to hold temperature and humidity steady.

🥣 Step-by-Step Doubanjiang Recipe

1. Make Fermented Broad Beans (Koji)

Soak broad beans overnight, then steam 20–25 minutes until al dente.

Cool to below 35 °C, sprinkle koji spores, and mix evenly.

Ferment covered at 30 °C/70% RH for 24 hours until white fuzz appears.
Break into rows for airflow, ferment another 24 hours until light green fuzz forms. (The fuzz you get is dependent on your koji spores. I used a strain typical for soy sauce)

*finished broad bean koji with green fuzz*

Weigh out the beans and combine with an equal weight of water. Calculate 5 % of the total mass of beans + water and add that amount of salt. Ferment 48 hours at 28 °C, stirring daily.

2. Prepare the Peppers

Wash, dry, deseed if less spice is desired. Chop roughly.
Rehydrate dried chilies in warm water.
Salt both fresh and dried peppers (5% by weight), drain for 1 hour.

Pulse in a food processor to a coarse, minced texture.

3. Assemble the Doubanjiang

Toast spices and grind to powder.
Mix minced peppers, fermented broad beans, and spices in a fermenting vessel.

*beans and chilies being mixed together*

Sprinkle a thin salt layer on top to prevent unwanted mold.
Cover with neutral oil (3–4 cm above surface).

Ferment at 30 °C for at least 3 months, stirring daily for 2 weeks, then weekly.