Meju Brick Making and Inoculation (메주 제조)

Korea; recorded in Goryeo-era texts. The meju tradition predates recorded history and likely developed simultaneously with settled soybean agriculture on the Korean peninsula ca. 2000 BCE

Meju (메주) is the fundamental inoculation block from which all Korean fermented soy pastes originate — dried cooked soybeans pressed into brick or ball forms and allowed to develop wild mould (primarily Aspergillus oryzae, Bacillus subtilis, and Rhizopus species) over 2–3 months of open-air fermentation. The process converts soybean protein via protease enzymes into amino acids and umami compounds that form the foundation of doenjang, ganjang, and gochujang. Traditional meju bricks are tied with rice straw (which carries natural Bacillus) and hung in a warm, ventilated space — the straw is not incidental but the inoculation medium.

Meju quality determines the ceiling of every Korean jang it produces. A weak meju produces flat, salty ganjang; an excellent meju produces layered, complex ganjang with the deep savoury notes that distinguish traditional joseon ganjang from commercial soy sauce.