1. Rinse the kombu:
Gently wipe the kombu with a damp cloth to remove any excess salt or debris. Avoid rinsing it under water to preserve its umami flavor.
2. Soak the kombu:
Place about 1 piece of kombu (about 10 cm) in 4 cups of cold water. Let it soak for 30 minutes to an hour.
3. Heat the water:
After soaking, slowly heat the water with the kombu over medium heat.
4. Remove before boiling:
Just before the water comes to a boil (around 60-80°C or 140-175°F), remove the kombu from the pot to prevent bitterness.
5. Add bonito flakes (optional):
For a richer flavor, you can add 1/2 cup of bonito flakes to the water and simmer for a few minutes, then strain the dashi.