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    Home » Recipes » Bento

    Kombu Onigiri (Simmered Kelp "Tsukudani" Rice Ball)

    Published: Jun 25, 2021 · Modified: Dec 10, 2021 by Yuto Omura

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    Have you've ever wondered if you can use your leftover kombu after making dashi? Well, the answer is, you can! In fact, you won't believe how delicious kombu can be until you try this recipe. This umami packed simmered kelp called "tsukudani" is one of the most popular onigiri fillings in Japan!

    Disclaimer: This post contains Amazon affiliate links. Sudachi Recipes earn a small percentage from qualifying purchases at no extra cost to you. See disclaimer for more info.

    Onigiri

    An onigiri (おにぎり) is a popular Japanese rice ball, most commonly shaped into a triangle or cylinder and then wrapped with a thin sheet of dry seaweed called "nori".

    They were also traditionally known as "omusubi" (お結び) or "nigirimeshi" (握り飯) but those words are not commonly used now, and if you do see them, it's more likely to be in writing rather than spoken.

    kombu onigiri in hand

    Onigiri are eaten with hands (no chopsticks or spoon) and commonly seen in bento boxes. They're a popular option of lunch, it's kinda like a rice equivalent to a sandwich after all!

    Onigiri Flavours

    Onigiri can be made with just plain salted rice, but actually they come in all kinds of different flavours! Fish, meat, vegetables, you name it! The sky's the limit when it comes to onigiri. Not only are they highly customizable, but also portable and convenient for when you're on the go!

    Here's a few popular flavours that you might see in Japan

    • Salmon (鮭)
    • Seasoned cod roe (辛子明太子)
    • Hard cod roe (たらこ)
    • Ume pickled plum (梅)
    • Seasoned kombu seaweed (昆布)
    • Tuna mayo (ツナマヨネーズ)
    • Seasoned bonito flakes (おかか)
    two kombu onigiri on a slate plate

    Today I'm going to show you how to make kombu onigiri, it's one of the top 5 onigiri flavours in Japan!

    Kombu (昆布)

    Kombu is a type of dried edible kelp and an essential ingredient in Japanese cooking. It's most common use is in "dashi", a soup stock that helps add umami and authentic Japanese flavour to dishes.

    tsukudani and dry kombu

    To make dashi, kombu is simply soaked until it's rehydrated and then heated up. I usually remove the kombu just before the water starts to boil as boiling kombu can release a bitter flavour into the dashi. Dashi is commonly used in miso soup, noodle broths and hot pot dishes.

    After the kombu is removed from the dashi, there's no need to throw it away! You can use it to make this delicious tsukudani!

    I use Hidaka Kombu for this recipe after using it to make dashi.

    What is Tsukudani (佃煮)

    Tsukudani is a traditional type of Japanese preserved food that has been simmered in a sweet and salty broth, most commonly made from soy sauce and sugars.

    It can be made with fish, meat or vegetables, but I've gotta say that the umami from the kelp makes kombu tsukudani my favourite!

    Since the broth is simmered down completely, the flavour is strong and concentrated. It's not really something you'd eat by itself, but it's the perfect accompaniment for rice, and the perfect onigiri filling!

    onigiri made with kombu tsukudani

    Preparing Kombu for Tsukudani

    It's best to use left over kombu for this dish. So after you've made dashi, don't throw the kombu away. You can either make tsukudani straight away, or save the kombu in the freezer for when you have time.

    If you want to start with dried kombu, I recommend soaking it in water over night before use. The water will become dashi and you can store it in the fridge for another recipe.

    The kombu takes a while to soften so I add 1 tsp of rice vinegar and 2 tbsp of sake to the water at the beginning. These additions help soften the kombu quickly.

    In the case that you finish the recipe but the kombu is still a bit hard, you can return it to the pan, add more water and simmer it down until the water is gone. The tsukudani won't lose flavour because you'll evaporate the water down, repeat until you achieve the desired softness.

    two kombu onigiri on a slate plate

    Kombu is the perfect onigiri filling or topping with rice! If you have leftover kombu tsukudani, you can keep it in the fridge for 2-3 weeks.

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    kombu onigiri

    Kombu Onigiri (Kelp "Tsukudani" Rice Ball)


    ★★★★★

    5 from 1 reviews

    • Author: Yuto Omura
    • Total Time: 50 minutes
    • Yield: 5-6 rice balls 1x
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    Description

    How to make delicious Kombu Tsukudani Onigiri. Japanese kelp simmered in soy sauce, mirin and sugar than wrapped in perfectly cooked sticky white rice. 


    Ingredients

    Scale
    • 50-60g used kombu kelp (approx 1 sheet - 12g when dry)
    • 500ml water
    • 2 tbsp sake
    • 1 tsp rice vinegar
    • 1 tbsp brown sugar
    • 1 tbsp mirin
    • 2 tbsp soy sauce
    • ½ tbsp sesame seeds

    For making the onigiri

    • 600g cooked rice (300g or 2 rice cups before cooking)
    • 1 bowl of ice cold water
    • 2 tsp salt
    • 5-6 pieces of nori cut to onigiri size (1 sheet of sushi nori will be enough for approx 4 onigiri)

    Instructions

    Before starting, make sure your kombu is already rehydrated. If you don't have used kombu, you'll need to soak it for 24 hours before making tsukudani. 

    Your rice can be cooking while you make the tsukudani. Use Japanese short grain white rice or sushi rice. You need the rice to be sticky so that it holds it shape. We recommend using a rice cooker or see how to cook Japanese rice on the stove here.

    Making Kombu Tsukudani

    1. Cut the soft used kombu into thin strips. (About 3mm or 1/10 inch thick)
    2. Add the sliced kombu to a pan with 500ml water, 2 tbsp sake and 1 tsp vinegar.
    3. Turn the heat on medium and bring to a rolling boil.
    4. Lower the heat and leave to simmer until the water has reduced by a bit less than half. (This should take about 20 minutes or so.)
    5. Add 1 tbsp brown sugar and mix. 
    6. Pour in 1 tbsp mirin and 2 tbsp soy sauce. Mix well and turn the heat back up to medium.
    7. Bubble until liquid is reduced to nothing, the kombu should be black with a thick soy sauce glaze. 
    8. Sprinkle in ½ tbsp of white sesame seeds and mix well. 

    Shaping Onigiri

    1. Submerge your hands into ice cold water and hold them there for 15-20 seconds.
      dip your hands in the icy water for about 20 seconds
    2. Rub 1-2 pinches of salt over your palms.
      Rub salt over your palms
    3. Take a handful of cooked rice, lightly flatten it and push a dent into the middle. Place 1-2 tsp of kombu into the dent and fold the rice over.
      a moving image showing how to add fillings to onigiri rice balls
    4. Fold your palm and push the onigiri into the crease of your hand. Press and turn until you've formed a triangular shape.
      shaping a salted onigiri by hand
    5. 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.
      kombu onigiri in hand

    Notes

    If the kombu is too hard after step 8 then add more water (100ml at a time) and simmer until the liquid is gone. Repeat until texture is soft to your liking.

    Store any left over kombu tsukudani in the fridge for 2-3 weeks. You can store leftover rice by letting it cool to room temperature and then storing in the freezer. 

    • Prep Time: 10 minutes
    • Cook Time: 40 minutes
    • Category: Rice
    • Method: Simmering
    • Cuisine: Japanese

    Keywords: kombu onigiri, kombu onigiri recipe, onigiri kombu, kombu tsukudani, kombu tsukudani recipe, making kombu filling for onigiri, simmered kombu, kombu filling, tsukudani recipe, how to make tsukudani,how to make onigiri kombu filling, onigiri fillings, kelp onigiri, kelp filling for onigiri, kelp rice ball, kombu rice ball

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    « Japanese Sesame Dressing (ごまドレッシング)
    Sakana no Nitsuke (Japanese simmered fish) »

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    Comments

    1. Kiki

      March 30, 2022 at 7:46 pm

      Thank you so much for this recipe! When I lived in NYC, onigiri from a local Japanese market was a frequent on-the-go snack for me, and kombu was my favorite onigiri filling. Now that I live in rural WV, it is hard to find prepared tsukudani, even on trips to Asian supermarkets in bigger cities. This recipe nails the flavor perfectly, and it can be made with ingredients that are not too hard to find (or that can be ordered online). I've made it several times now, most recently in a bigger quantity - it keeps quite well in the fridge. You are a lifesaver - thank you!

      ★★★★★

      Reply
      • Yuto Omura

        March 30, 2022 at 10:16 pm

        Hi Kiki,
        I'm so happy to hear you're enjoying the recipe and can now enjoy kombu onigiri anytime! I've never seen kombu onigiri outside of Japan, I'm sure you can only find it in very specific Japanese supermarkets. Thank you for your kind rating 🙂

        Reply

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    Thanks for visiting Sudachi Recipes. My name is Yuto and I'm a Japanese guy with a passion for food. Here I share tasty and accessible recipes so that you can bring a taste of Japan to your own kitchen.

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