Kombu

Kombu is a thick, dark green kelp that is harvested, sun-dried and sold in stiff sheets. It is very rich in glutamate, the compound behind umami, so a small piece makes stock taste deeply savory. With bonito flakes, it is one of the two ingredients in classic dashi.

How to use it

To make a simple kombu stock for about 1 liter (4 cups):

1. Wipe a 10 g piece of kombu, about 10 by 10 cm (4 by 4 inches), with a damp cloth. Do not wash off the white powder on the surface. It is part of the flavor.
2. Soak it in 1 liter of cold water for at least 30 minutes, or overnight in the fridge for a deeper taste.
3. Heat the water slowly and take the kombu out when small bubbles appear around the edge, just before it boils.

You now have a plant-based stock. Add bonito flakes for full dashi, or use it as it is for vegan miso soup.

Kombu has other uses too:

• Add a strip when cooking dried beans. It seasons them and softens the skins.
• Lay a piece in the pot when cooking rice for sushi.
• Reuse the soaked kombu by slicing it thin and simmering it with soy sauce, mirin and sugar until tender, to serve with rice.

Substitutes

There is no direct swap. Dried shiitake mushrooms soaked in water give a similar savory stock, with an earthier taste. Wakame and other seaweeds add sea flavor but much less depth. Instant dashi powder works if you just need dashi.

How to store it

Keep dried kombu in a sealed bag in a cool, dry place. It keeps for a year or more. Once soaked, keep it in the fridge and use it within a few days.

Common mistakes

• Boiling it. The stock turns slimy and bitter.
• Scrubbing off the white powder.
• Using a lot. Kombu is very high in iodine, so treat it as a seasoning, not a vegetable to eat in large amounts every day.