Mushroom Dashi

Wipe the kombu surface with a barely damp cloth to remove any excess white powder — that white bloom is glutamic acid precipitate, the source of the umami, so do not rinse it away under water. Place both the kombu and the dried shiitake in a clean glass jar or bowl and pour over the cold water. Cover and refrigerate for a minimum of 6 hours, ideally overnight (8 to 12 hours). Cold extraction is the defining technique here: low temperature extracts the fragrant, clean umami compounds first while leaving behind the sulfurous, bitter notes that heat would draw out. Do not rush this with hot water.

Remove the kombu first with tongs — reserve it for another use. Lift out the shiitake and squeeze them gently over the jar to return their soaking liquor; reserve the mushrooms for miso soup, nimono, or braised vegetables. Strain the dashi through a fine-mesh sieve lined with a damp paper towel or cheesecloth to catch any grit or fine particles. Do not press or wring the cloth, which would cloud the dashi. The finished dashi is now ready; use it immediately or refrigerate for up to 3 days.

The dashi is technically complete unseasoned — it is a base. For miso soup, ladle it into a saucepan and warm to just below a simmer (70 to 75°C); dissolve miso in a ladle of hot dashi before stirring in. For use as a cooking liquid or sauce base, season with a small amount of usukuchi (light soy sauce) and mirin to taste. Never boil the finished dashi: the volatile aromatic compounds that make it taste alive rather than flat are driven off at rolling boil temperatures. Gentle warmth preserves them.