Dashi (Kombu and Katsuobushi)

Gently wipe the kombu surface with a barely damp cloth to remove any surface debris — do not wash it. The white powder on the surface (mannitol) is umami; do not remove it. Place kombu in a pot with cold filtered water. Cover and steep in the refrigerator overnight, or a minimum of 3 hours at room temperature. The cold steep extracts the complex polysaccharides and glutamates from the kombu without the bitterness that comes from heating. The water will turn a pale, clear gold.

Place the pot over medium-low heat. Slowly bring the water to temperature, watching carefully — the goal is to reach 60–65°C (140–150°F) and hold it there for 10 minutes. Do not let it boil. Boiling extracts bitter compounds from the kombu. Use a thermometer. Alternatively: watch for the first small bubbles forming at the bottom of the pot and on the kombu surface — these appear at approximately 60°C. Remove the kombu before the water reaches 70°C.

Remove the kombu (reserve it for making niban dashi or braised kombu dishes). Bring the kombu water to just under a boil — you want to see rolling movement at the surface but not a full boil. Remove from heat entirely. Add all the katsuobushi at once. Do not stir. Allow the bonito flakes to bloom and sink naturally — this takes 2–3 minutes. The flakes will first float, absorb liquid and darken, then slowly sink to the bottom as they give up their inosinate.

Line a fine-mesh sieve with a clean cheesecloth or coffee filter. Pour the dashi through slowly without pressing the solids — pressing extracts bitter compounds. Let it drain freely. The finished ichiban dashi (first draw) should be a clear, golden-amber liquid of profound depth. Discard the spent katsuobushi or reserve for making furikake rice seasoning. Use dashi immediately or refrigerate for up to 3 days. Do not freeze — freezing breaks down the delicate glutamate and inosinate compounds and dulls the flavor.