How to Make Meju blocks
Meju (메주) are fermented soybean blocks that form the foundation of Korean fermented sauces including doenjang (soybean paste), ganjang (soy sauce), and gochujang. These brick-shaped cakes are inoculated with wild molds and bacteria during a months-long drying process, developing the complex flavors essential to Korean cuisine.
Category: Legumes & Soy · Method: Fungal/Mold · Time: 2-6mo · Difficulty: 3/5 · Yield: varies · Temp: 18-22°C
History
Meju-making dates back over 2,000 years in Korean history, with techniques passed down through generations. Traditionally made in late fall after the soybean harvest, meju blocks were hung in homes to ferment through winter. The practice connects to Korea's agricultural cycles and represents culinary heritage.
Ingredients
- 4 cups (800g) Dried soybeans — Yellow soybeans
- Several handfuls Rice straw — For wrapping and inoculation
- As needed Cotton string — For tying
Equipment
- Large pot for boiling
- Mortar and pestle or food processor
- Brick molds or hands for shaping
- Drying rack
- Well-ventilated hanging space
Instructions
Soak and cook beans
Soak soybeans overnight (12-24 hours). Boil or steam until they are very soft and can be easily crushed between your pinky and thumb. This usually takes 4-5 hours of boiling or 2 hours in a pressure cooker.
Time: 12-24 hours
Tip: Properly cooked beans should be a deep amber color and have a nutty, sweet aroma.
Initial drying and surface hardening
Place the formed blocks on rice straw in a cool, well-ventilated area for 1-2 weeks. The goal is to dry the exterior so the blocks hold their shape and develop a 'skin' before the warm fermentation phase.
Time: 1-2 weeks
Tip: Turn the blocks regularly to ensure even drying and prevent moisture from pooling at the bottom.
Warm fermentation (Deu-iu-gi)
This is a critical phase for Bacillus subtilis development. Place the blocks in a warm environment (25-30°C), ideally in a box lined with rice straw or wrapped in blankets. This encourages the growth of beneficial bacteria and molds from the straw into the heart of the block.
Time: 2-4 weeks
Tip: The blocks should feel warm to the touch as the microbial activity generates its own heat.
Hanging and secondary fermentation
Tie the blocks with rice straw and hang them in a cool (15-20°C), well-ventilated area. This slow drying process allows the enzymes to break down the soy proteins into amino acids, creating the deep umami flavor.
Time: 1-3 months
Tip: Avoid areas with high humidity to prevent the growth of undesirable toxic molds.
Fermentation Timeline
- Week 1-2: Initial drying — Surface hardens. Cracks form. Blocks shrink slightly.
- Month 1: Mold development — White fuzzy mold appears. Fermented smell developing.
- Month 2-3: Deep fermentation — Mold coverage increases. Strong umami aroma. Interior fermenting.
- Month 4-6: Mature meju — Blocks are light, dry, heavily molded. Ready for sauce making.
Signs of Success & Spoilage
Good signs
- White or light yellow fuzzy mold (mostly Rhizopus or Mucor species)
- Golden brown or greyish exterior
- Deep, earthy, fermented aroma (similar to nuts or chocolate)
- Blocks feel significantly lighter and sound hollow when tapped
- Interior is dark brown and dry
Warning signs
- Bright yellow or greenish-yellow fuzzy mold (potential Aspergillus flavus/aflatoxins)
- Excessive black mold covering the surface
- Slimy or wet texture on the surface
- Foul, putrid, or rotten smell (indicates spoilage rather than fermentation)
- Presence of maggots or mites
Troubleshooting
- Bright yellow or neon green mold
- Cause: Contamination by toxic Aspergillus species due to poor airflow or high humidity Solution: Discard the block immediately. These molds can produce heat-stable aflatoxins that are dangerous to consume.
- No mold growth after warm phase
- Cause: Temperature too low or beans were too dry Solution: Ensure the environment stays between 25-30°C and that the rice straw is fresh and in direct contact with the blocks.
Storage
Keep hanging in dry, ventilated area until use Keeps Use within 1 year of making. Break apart and soak in brine to make doenjang and ganjang.
Health Benefits
- High protein
- Probiotics and enzymes
- B vitamins (from fermentation)
- Isoflavones
- Easily digestible protein
- Traditional medicinal uses
Serving Suggestions
- Base for doenjang (soybean paste)
- Base for ganjang (soy sauce)
- Ingredient in gochujang
- Traditional Korean sauce foundation
- Not eaten directly
- Essential Korean pantry item
Related Legumes & Soy Ferments
Other Fungal/Mold Ferments
- Miso — Condiment
- Furu (tofu cubes) — Legumes & Soy
- Tempeh gembus — Legumes & Soy
- Stinky tofu — Legumes & Soy
- Blue cheese — Dairy
- Brie — Dairy
- Camembert — Dairy
- Roquefort — Dairy