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Kombu Onigiri (Kelp "Tsukudani" Rice Ball)

5 from 1 vote
By Yuto Omura
https://sudachirecipes.com
Have you ever wondered if you can use your leftover kombu after making dashi? Well, the answer is you can! You won't believe how delicious kombu itself can be until you try this recipe. This umami-packed simmered kelp called "Tsukudani" is one of Japan's most popular onigiri fillings!
Prep Time10 minutes
Cook Time40 minutes
Total Time50 minutes
Course Bento, Lunch, Snacks
Cuisine Japanese
Servings 6 rice balls
Prep Time: 10 minutes
Cook Time: 40 minutes
Total Time: 50 minutes
Course: Bento, Lunch, Snacks
Cuisine: Japanese
Servings: 6 rice balls

Equipment

Ingredients 
 

  • 50 g rehydrated kombu (kelp)
  • 500 ml water
  • 2 tbsp sake
  • 1 tsp rice vinegar
  • 1 tbsp light brown sugar
  • 1 tbsp mirin
  • 2 tbsp soy sauce
  • ½ tbsp white sesame seeds

For making the onigiri

  • 600 g cooked Japanese short-grain rice
  • 2 tsp salt
  • 6 pieces sushi nori seaweed cut to rice ball size, 1 sheet of sushi nori will be enough for approx 4 onigiri

Instructions 

  • Before starting, make sure your kombu is already rehydrated. It needs to soak for at least 1 hour before making tsukudani, and the leftover liquid can be used as kombu dashi. 
    kombu mizu dashi step 2
  • You can cook the rice while the tsukudani is simmering. Use Japanese short grain white rice or sushi rice. The rice needs to be sticky so that it holds it shape. Use a rice cooker or check out my how to cook Japanese rice on the stove recipe.
    mixing rice in a black cooking pot with rice paddle

Making Kombu Tsukudani

  • Cut 50 g rehydrated kombu into thin strips. (About 3mm or 1/10 inch thick)
    rehydrated kombu cut into matchsticks (julienned) in a glass bowl
  • Add the sliced kombu to a pan with 500 ml water, 2 tbsp sake and 1 tsp rice vinegar.
    Bring to a rolling boil over a medium heat, then lower the heat and simmer until the water has reduced to a little less than half. This should take approximately 20 minutes.
    simmering kombu in water
  • Add 1 tbsp light brown sugar, 1 tbsp mirin and 2 tbsp soy sauce. Mix well and increase the heat back to medium.
    simmering kombu with water and condiments
  • Continue to boil until the liquid is completely reduced, mix often to prevent burning. Once thick, sticky and dark, sprinkle in ½ tbsp white sesame seeds and mix well. 
    reduced kombu tsukudani with sesame seeds in a pan

Shaping Onigiri

  • Sprinkle salt over your rice ball mold (or slightly dampened hands) and shape your rice. Place 1-2 tsp of the kombu tsukudani in the center and encase.
    rice in an onigiri (rice ball) mold with kombu tsukudani in the center
  • For more details on how to shape onigiri by hand, check out my 3 ways to shape perfect onigiri post.
    shaping onigiri rice ball by hand
  • Wrap the onigiri with a sheet of nori and enjoy! You can also place the kombu tsukudani on top of the rice ball for decoration.
    a hand holding kombu onigiri wrapped with nori

Notes

If the kombu is too hard after reducing all the liquid and condiments, add more water (100ml at a time) and simmer until the liquid is gone and mix often to ensure even cooking. Repeat until texture is softened to your liking.
Any leftover kombu tsukudani should be stored in the fridge and used within 2-3 weeks. The rice balls themselves can be wrapped in plastic wrap and stored in the freezer for up to 1 month. Store without nori and defrost in the microwave. Refrigeration is not recommended for rice balls.