Doenjang meju

What meju is

Meju is cooked soybean mass formed into a brick or another regional shape and fermented as a solid. It is not a finished seasoning. Its job is to become the raw material for Korean jang: the brick is brined later, and its liquid and paste fractions become ganjang (soy sauce) and doenjang (soybean paste).

The word covers several related products. Historical sources use maljang, mejo and meju, and the Academy of Korean Studies entry treats them as names for the same brick material. Gochujang-meju is a different form that may include grain and a different shape, and it is not the subject of this page.

Attestation and the Joseon record

The Academy of Korean Studies entry quotes a maljang method from the Joseon-period Sangayorok, with instructions for the first and second lunar months. It also records a wooden tablet from the Mado 1 shipwreck, dated 1207–1208, that lists maljang among the cargo collected in southern coastal waters and sent toward Songdo. The shipment context shows the material moving in trade in the medieval period. It does not show when meju was first made.

Seasonal references vary. The same entry cites a November reference in the Nongawollyeongga, so the calendar in the records is not a single rule.

How a household brick is made

The National Folk Museum of Korea presents an Angye-ri account of winter meju-making around Ipdong, the beginning of winter. Soybeans are sorted and rinsed, then cooked slowly in an iron cauldron for about six to seven hours according to an interview. The hot beans are pounded in a stone mortar, shaped in a wooden mould lined with hemp, bound with rice straw and hung under the eaves to dry and ferment through the winter. The account names a sorting board, cauldron, mortar and pestle, mould, straw and eave-drying place as the tools of this practice.

The account gives no soybean quantity, brick size, measured temperature, endpoint or storage protocol. It describes one community practice and is not a validated recipe for a home kitchen.

What the microbes do

Traditional meju is not made with a selected starter. A 2014 study of doenjang-meju made at a manufacturer, with soybeans soaked overnight, steamed at 120°C for two hours, cooled, crushed and moulded, found that the brick exterior and interior communities differed. Bacillus predominated on the outside, while the interior had more facultative and anaerobic groups. The authors trace bacteria largely to the moulding equipment and fungi mainly to the environment, including shelves, air and rice straw.

A 2022 study of eight makers from different regions found distinct bacterial community patterns, including Bacillus-dominant and lactic acid bacteria-dominant examples. A 2024 study of a sample from Icheon used its own staged drying and fermentation schedule. Together these studies describe mixed communities that vary by batch, maker and position within the brick. They do not establish a universal inoculum, and the Bacillus, Mucor, Geotrichum and Aspergillus names summarize organisms detected in samples, not a recipe to copy.

A 2013 mycoflora study of soybeans used for meju adds that the grain itself carries fungi, so both the raw material and the environment matter.

From brick to doenjang and ganjang

Jang-making takes the dried brick further. The brick is brined, and over months the salt and the microbes change it. The liquid fraction is separated as the soy sauce, ganjang, and the solid fraction is mixed and aged as doenjang. A 2020 household survey reports that 71.3 percent of surveyed households used homemade meju for doenjang.

The brick is therefore an intermediate. Judging it alone does not tell a cook whether the later product is sound.

Season and regional practice

A 2018–2019 household survey found that 50.7 percent of respondents who answered the season question made meju in November–December and 36.3 percent in September–October. Provinces at higher latitude more often reported September–October, and lower-latitude groups more often reported November–December. The survey used a non-probability snowball sample and its Jeju sample was small, so the figures describe reported practice and are not a national calendar.

Locations also vary. Households reported yards, rooms and balconies. The 2014 study and the 2022 study sampled makers at specific sites, and those sites are study locations, not origins.

Safety and what is not established

No source reviewed establishes a validated household method for meju. The sources do not give a home shelf life, a contamination response, or a safe endpoint for drying and fermentation. Mould on the surface is not a test of safety, and neither are smell, taste or appearance.

Overly thick or large bricks dry slowly, and the museum account names a local concern about unwanted mould. These are folk observations, not validated rules. Anyone making meju at home should treat it as an uncontrolled traditional process and seek food-safety guidance before relying on it.