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Boiled soybeans are shaped into blocks called meju, then dried and colonized by airborne molds and bacteria. The blocks are submerged in salt brine in earthenware crocks for months. The liquid is drawn off as ganjang (soy sauce) and the mashed solids become doenjang (soybean paste), so the two foundational seasonings are one batch split into liquid and solid.
Korean cooking can be read as built on jang the way French cooking is built on mother sauces. Ganjang, doenjang, and gochujang are finished flavor bases that a cook dilutes, blends, and layers rather than builds from scratch. Much of a dish's depth is therefore decided before cooking starts, by which jang is used and how old it is.
Traditional jang gains its complexity from slow, seasonal fermentation shaped by a specific maker's methods, local microbes, and years of aging. Mass-produced versions shorten or skip that process and make up for it with additives, which yields a flatter flavor. A cook's most consequential choice is where the jang comes from, which is why the author sources directly from village makers.