Cold-Brew Kombu Dashi
A clean, gently savory Japanese kelp broth made by steeping kombu in cold water. It's vegan, needs almost no effort, and works as a base for miso soup, noodle broths, simmered vegetables, and hot pots.
- Prep
- 5 min
- Cook
- —
- Wait
- 8 hr
- Total
- 8 hr 5 min
- Makes
- About 4½ cups (1,050 ml) dashi, enough for 4 generous bowls of soup (about 1 cup each)
Steps
Before you start
- Plan ahead: the kombu needs at least 4 hours in the fridge, and 8 hours (overnight) gives the best flavor.
- Do not wash the kombu under running water or scrub it. The white powder on the surface is natural mannitol and glutamates that carry flavor. Just wipe it with a dry or barely damp cloth.
- Use filtered or soft water if your tap water is hard or heavily chlorinated, since it can mute the delicate flavor.
- Use a clean glass jar or pitcher with a lid (2 quarts / 2 liters) so the dashi has room and doesn't pick up fridge odors.
Wipe the kombu
- Wipe the surface of the 15 g (½ oz) kombu with a dry or barely damp cloth to remove any grit.
- Leave the white powder on the surface, because it carries flavor.
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Ready when: The surface is free of visible grit, and the white bloom remains.
Tip: Do not rinse or scrub. That removes the umami-rich powder.
Score the kombu
- Use kitchen scissors to cut 2 or 3 small slits, about 1 inch (2.5 cm) long, along the edges of each piece.
- This helps the kombu release flavor into the water.
- Keep the pieces whole, since small bits are harder to strain out.
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Ready when: Each piece has a few slits along the edges but is still in one piece.
Combine in jar
- Place the kombu in a 2-quart (2 liter) glass jar or pitcher.
- Pour in 5 cups (1,180 ml) cold filtered water, making sure the kombu is fully submerged.
- The jar will be about two-thirds full.
- Cover with a lid.
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Ready when: All kombu is covered by water.
Tip: Press any floating kombu down with a clean spoon so it steeps evenly.
Steep in fridge
- Refrigerate the jar for at least 4 hours, ideally 8 hours or overnight.
- Cold steeping extracts glutamates slowly and avoids the slimy texture and bitterness that can come from hot extraction.
- Don't go past 24 hours, or the broth may turn slightly slimy and strongly briny.
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Ready when: The water looks pale golden-green, smells lightly of the sea, and tastes mildly savory and slightly sweet. The kombu is soft and pliable.
Tip: Taste at 4 hours. If it is too mild, keep steeping.
Remove the kombu
- Lift the kombu out with clean tongs or fingers and set it aside.
- Pour the dashi through a fine-mesh strainer into a clean container or measuring cup to catch any small bits.
- The kombu absorbs some water, so you should have about 4½ cups (1,050 ml).
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Ready when: The dashi is clear with no floating bits, and the kombu is out.
Tip: The used kombu can be simmered in soy sauce and mirin as tsukudani or added to a second, weaker dashi.
Use or store
- Use the dashi right away, cold or warmed gently.
- If heating, bring it to a bare simmer over medium-low heat and don't boil hard, as boiling can make the flavor sharper.
- Season with a little salt or soy sauce, or build into miso soup or noodle broth.
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Ready when: Small bubbles form at the pan edge and steam rises, but there is no rolling boil.
Tip: Add miso off the heat so its flavor stays delicate.
Good to know
Tips
- Better kombu, such as rishiri or ma-kombu, gives a cleaner, sweeter broth, but any dried kombu works.
- For a stronger broth, use 20 g kombu for the same amount of water instead of steeping longer.
- For a quicker version, warm the kombu and water over low heat to about 140°F (60°C) and hold for 30 to 60 minutes, then remove before it simmers.
- Do not boil the kombu, since this can make the broth bitter and slimy.
Make ahead
Make it up to 1 day ahead: the cold steep is designed for overnight, and you can strain it the next morning.
Storage & reheating
Refrigerate strained dashi in a covered container for up to 3 days. Freeze for up to 1 month, such as in ice cube trays, then transfer to a bag. Thaw in the fridge or warm gently on the stovetop over medium-low heat. Don't store it at room temperature for more than 2 hours.
Substitutions
- dried kombu (kelp) → Dried shiitake mushrooms (about 3 medium). Adds a deeper, earthier flavor. Use alone or with kombu for a richer vegan dashi.
- dried kombu (kelp) → Kombu dashi granules or powder. Follow the package directions, as strength varies. It is often saltier, so reduce added salt.
- filtered water → Spring water. Soft, low-mineral bottled water works well if your tap water is hard.
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- Meal
- Lunch
- Cuisine
- Japanese
- Method
- No-Cook
- Quick & Easy
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