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1
Rinse the soybean sprouts in cold water, inspecting each handful to confirm the yellow soybean heads are intact and firm, because a broken or blackened head will turn mealy and bitter once heat is applied. Discard any damaged sprouts, then place the rest in a small saucepan with just enough water to cover the base by 1 cm — shallow water builds steam faster than a deep bath, keeping cooking time precise. The pan must not be overcrowded or the sprouts nearest the base will overcook before the rest have softened.
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2
Place the lid on the saucepan and bring to a vigorous boil over high heat, keeping the lid firmly in place throughout cooking so the trapped steam cooks the top layer as evenly as the water cooks the bottom — lift it once and the heat escapes, the timing shifts, and you lose control of the texture window. For crunch (아삭), cook covered for 1–2 minutes from the moment steam is visible at the lid's edge, stopping when the stems are translucent at the base yet still snap cleanly; for soft (부드럽게), cook covered for 3–5 minutes, stopping when a stem bends without resistance and yields fully under gentle pressure between two fingers. This is where the dish lives or dies: even 30 seconds beyond the crunch window eliminates the defining snap of 아삭 kongnamul.
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3
Drain the sprouts immediately and thoroughly in a colander the moment they reach their texture, because residual heat in the pan continues cooking them even off the flame. For the crunch version, follow at once with a cold water shock to arrest cooking entirely, then drain again until no standing water remains; for the soft version, drain without shocking. Press gently to expel residual water, since undrained sprouts will dilute the dressing as surely as poorly squeezed spinach namul.
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4
Allow the drained sprouts to cool until just warm to the touch — not hot, not cold — because warm sprouts open to an oil-based dressing where cold sprouts will simply shed it. Combine the chosen dressing ingredients in a bowl, add the sprouts, and toss by hand, turning repeatedly until every stem is evenly coated. The yellow soybean heads should remain slightly firm; if they have collapsed to mush, the blanch has run too long.
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5
Taste for seasoning, adjusting salt or guk-ganjang in small increments so the banchan sits lightly on the palate rather than asserting itself, since its role is to reset the mouth between stronger banchan. Serve at room temperature for fresh eating alongside rice. If destined for bibimbap or kongnamul-guk, the soft-version sprouts may be held, as they will absorb further liquid well in their final context.