Kongnamul-guk (Soybean Sprout Soup)

Variations

• Spicy version: Add gochugaru and cheongyang chili for heat.
• Haejang-guk: Add rice with salted shrimp and chili for a hangover soup.
• With dried pollock: Add bukeo for an even cleaner, deeper broth.
• With egg: Swirl in a beaten egg at the end for softness.

Tips

• What has to leave is a raw note off the bean, and the lid either holds it in or lets it go. Blanching vegetables gives bean sprouts a subsection of their own. They have no chlorophyll and so no colour to protect; what has to leave is the raw green note that comes off asparagine, an amino acid the bean carries. Left off the whole way, that note simply goes with the steam. Left on the whole way, it stays in the pot and boils off over the full time. Only opening it partway cools the steam on the lid and drops it straight back in. So the line below is not "keep it covered" — it is "do not change it."
• The rule runs backwards from the one for green vegetables. The same guide says to blanch anything green with the lid off. There what has to escape is the organic acid heat releases from the cells, which strips the magnesium out of the chlorophyll and turns the colour olive. That is the contrast sigeumchi-namul and kongnamul-muchim draw while pointing at each other.
• This broth is the sprout water itself. Kongnamul-muchim says not to throw that water away: anything high in oxalic acid, like spinach, gets discarded, but bean sprout water is a broth as it stands. The side dish hands it on to another pot; this soup puts it straight in the bowl. Same ingredient, same pot — one of them is after the sprouts and the other is after the liquid.
• Salt alone leaves it clear and hollow. Galbitang sets out the same problem: dark soy carries sugar and colour and turns a broth brown, while salt alone stays clear but tastes hollow, so the standard is a base of soup soy sauce adjusted with salt. Kalguksu gives the limit from the other end — seasoning with soup soy sauce alone darkens the broth. Salted shrimp is the third option, and kongnamul-gukbap puts its advantage in one line: "it adds savour where salt only adds salt" — salt brings saltiness and nothing else, while a ferment brings both at once (building umami). That page also says to add it as it is rather than dissolving the liquor into the pot.
• The 5-6 minutes is set by the bean, not the stalk. Kongnamul-muchim gets the beans cooked through in 4-5 minutes under a lid with half a cup of water — but it then lifts them out and stops the cooking dead in cold water. A soup has no such stop. The sprouts go on cooking in hot broth, so the moment you kill the heat is the last of the cooking time, which is why the same ingredient wants a slightly shorter run here than in the side dish.
• Keep the lid on the whole time, or off the whole time — opening it midway brings out a beany smell.
• An anchovy-kelp stock makes it far more refreshing and savory than plain water.
• Season with salted shrimp or soup soy sauce to keep the broth clean and bright.
• Don't overcook the sprouts — 5-6 minutes keeps them crisp.
• Add the garlic near the end so its aroma stays.