Ingredients

   
10g kombu (dried kelp)
1000g water

Steps

Cold Brew (hands-off, delicate flavor)

  1. Combine kombu and water in a jar or bowl. Refrigerate 3–9 hours.

  2. Remove kombu. Use immediately or refrigerate.

Simmer (faster, stronger flavor)

  1. Combine kombu and water in a pot. Soak at least 30 minutes until kombu softens.

  2. Heat over very low heat for about 10 minutes. When small bubbles appear on the surface, turn off heat and remove kombu immediately. Do not let it boil.

Notes

  • The ratio is 1% kombu by weight of water. Scale freely: 5g kombu to 500g water, 10g to 1000g, etc.
  • Do not rinse the kombu. The white powder on the surface is natural umami (glutamic acid). Wipe gently with a damp cloth if dusty.
  • Do not boil. Boiling releases slimy compounds and a strong seaweed odor that muddies the flavor.
  • Do not soak longer than 10 hours — the dashi will turn cloudy and develop off-flavors.
  • Use as large a piece of kombu as possible. More cut surfaces = more slime released.
  • Cold brew produces a cleaner, more delicate dashi. Simmering produces a richer, stronger one.
  • Keeps refrigerated 3 days, frozen 1 month.
  • Save the used kombu — it can be reused for a weaker second dashi, or repurposed into kombu chips or shio kombu.