Name: Okinawan Kombu & Tofu Simmer
Prep time: 15 min
Cook time: 25 min
Total time: 40 min
Yield: 4
Cuisine: Japanese
Ingredients: 40g dried kombu (about 4 large sheets); 400g firm tofu, pressed 20 minutes and torn into rough pieces; 2 carrots, cut into matchsticks; 1 onion, sliced thin; 500ml the kombu soaking water, reserved; 2 tbsp soy sauce or tamari · 1 tbsp mirin; 1 tbsp toasted sesame oil · 1 tbsp neutral oil; 1 tbsp toasted sesame seeds · 2 spring onions, sliced; A thumb of ginger, julienned

Kombu does not grow in Okinawan waters. It grows in Hokkaido, at the other end of Japan — and yet for most of the last two centuries Okinawa consumed more of it per head than any other prefecture, brought south along the trade routes and folded into the everyday cooking until it became a defining ingredient.

Kombu irichi is the plainest expression of that: seaweed cut into ribbons, braised with tofu and whatever root vegetable is around, seasoned with almost nothing. It is cheap, it keeps, and it is the dish that fills the seaweed-shaped hole in most people's idea of the Okinawan diet.

The Longevity Science

Iodine: the one nutrient where more is worse

Kombu is the most iodine-dense food in common use anywhere — far denser than nori or wakame — and this is the rare case where the honest advice runs the opposite way to the usual supplement logic. Japan is an iodine-replete country without any iodine fortification, because seaweed supplies it; a 2026 nationwide survey of Japanese adults measured urinary iodine, thyroid function and thyroid volume precisely because habitual intake there sits at the top of the global range. Separately, a 2026 European Journal of Nutrition study of habitual seaweed eaters found that some species carry high enough iodine to push intake into excess, and measured thyroid function before and after a six-week cessation. Iodine follows a U-shaped curve: too little causes goitre, too much can trigger thyroid dysfunction in susceptible people. Eat this dish as Okinawans do — regularly, in modest portions — and do not decide that daily kombu tea is a good idea.

Highest

Kombu's iodine density among foods in ordinary use

U-shaped

The relationship between iodine intake and thyroid risk — bad at both ends

The Ingredients

40g dried kombu (about 4 large sheets)
400g firm tofu, pressed 20 minutes and torn into rough pieces
2 carrots, cut into matchsticks
1 onion, sliced thin
500ml the kombu soaking water, reserved
2 tbsp soy sauce or tamari · 1 tbsp mirin
1 tbsp toasted sesame oil · 1 tbsp neutral oil
1 tbsp toasted sesame seeds · 2 spring onions, sliced
A thumb of ginger, julienned

How to Make It

Soak the kombu and keep the water

Cover the kombu with 600ml of cold water and leave 30 minutes until pliable. Keep that water — it is now dashi, and it is the entire seasoning base of the dish. Lift the kombu out, roll the sheets and slice into 5mm ribbons.

Press and tear the tofu

Press the tofu between two plates with something heavy on top for 20 minutes, then tear rather than cube it. Torn faces hold sauce; cut faces slide off it.

Brown the tofu first

Heat the neutral oil in a wide pan and colour the tofu on two sides without crowding, 6–8 minutes. Take it out and set aside. Doing this first is what stops the tofu disintegrating in the braise.

Build the braise

Soften the onion, carrot and ginger 4 minutes in the sesame oil. Add the kombu ribbons, the reserved soaking water, soy and mirin. Simmer uncovered 15 minutes — the kombu should go from leathery to yielding and the liquid reduce by half.

Return the tofu and finish

Fold the tofu back in and simmer 5 minutes more to take on the sauce. Off the heat, scatter sesame seeds and spring onion. It is better after twenty minutes standing, and better still the next day.