Kombu Onigiri

Kelp Tsukudani Rice Balls

Kombu tsukudani is a classic onigiri filling with an intense umami flavour, salty and spicy. Discover how to make it at home with simmered kelp and have fun stuffing it into delicious Japanese rice balls.

Kombu Onigiri (Kelp Tsukudani Rice Balls)


Nutrition per serving
Net Carbs33.8 g12.3%
of which Sugars3.2 g3.5%
Fibers0.5 g1.9%
Fats1 g1.5%
of which Saturates0.2 g0.9%
of which Omega 30 g1%
Proteins3.4 g7.5%
Calcium22 mg2.2%
Vitamin A9 mcg1.3%
Vitamin C2 mg2.9%
Iron0.9 mg5.9%
Potassium69 mg2%
Sodium547 mg23.8%
Cholesterol0 mg0%
Kcal158 7.9%
Macro split
  • net carbs 87%
  • sugars 8%
  • fats 3%
  • saturates 0%
  • proteins 9%
  • fibers 1%
*RDA based on a 2000 kcal diet;
**Nutritional data sources: USDA, food labels.
158 per serving

Don't know what to do with leftover kombu? Then, use it up in one of Japan's most popular onigiri recipes: kombu tsukudani rice balls. They're savoury, flavourful, and so addictive! Let's make them together!

Kombu onigiri are balls of cooked sushi rice stuffed with kelp tsukudani and wrapped with nori strips. Great as a portable snack or addition to your bento box.

The Japanese word tsukudani (佃煮) refers to a food preparation where seafood, meat, veggies, or seaweed has been slowly simmered in a sweet and savoury sauce.

So, kombu tsukudani consists of kombu strips boiled in soy sauce, sugar, and rice vinegar until glossy and tender. Chillies and roasted sesame seeds are added for extra flavour and texture.

Kombu is a type of seaweed also known as kelp. It's widely used in Japanese cuisine, especially for preparing dashi broth, the base of the famous miso soup.

And making kombu tsukudani is a clever way of using up the boiled kombu leftover from preparing miso soup!

But don't worry, you don't have to make the soup to prepare these onigiri.

You can also start with dried kombu and rehydrate it before cooking it. Below, we'll give you the option to use one or the other.

Kombu tsukudani has an intense umami flavour, and it's sweet, salty, and spicy. The perfect filling to make delicious Japanese seaweed rice balls!

In the steps below, we'll show you how to cook the onigiri rice, fill the rice balls with seaweed, and shape them into perfect triangles.

We'll also share extra tips and tricks for the best results, so keep reading and follow along!

And if you're looking for more delicious onigiri recipe ideas, we're sure you'll love this vegan tuna onigiri and crispy yaki onigiri. Give them a go!


Measuring System
Kombu Tsukudani
Kombu (soaked weight)80 g
Rice Vinegar11/2 tbsp
Caster Sugar2 tbsp
Gluten-Free Soy Sauce2 tbsp
Red Chillies2
Roasted Sesame Seeds1 tbsp
Japanese Short-Grain White Rice300 g
Salt1 tsp
Nori Sheets2
Water700 mL

Step 1

Let's prepare the kombu tsukudani first.

Usually, you should use the spent, boiled kombu (kelp seaweed) leftover from other Japanese dishes like dashi broth for miso soup.

But you can also start with the dried kombu if you prefer.

Use 8 g of dried kombu for every 80 g boiled kombu. Soak the seaweed in water for an hour or until rehydrated. Alternatively, add the kombu to a pot of water, bring it to a boil, and remove the seaweed.

Now, slice the soaked or boiled kombu into thin strips, about 3mm thick.

sliced kombu for tsukudani

Step 2

Transfer the sliced kombu into a pan.

Add 300 mL of water, rice vinegar, sugar, soy sauce, and thinly sliced chillies for a spicy finish.

You can swap rice vinegar with mirin (sweet rice vinegar), decreasing the sugar by 1 tbsp.

Bring all to a boil over medium heat.

kombu tsukudani ingredients in a pot

Step 3

Once boiling, simmer the kombu without covering it for 20-30 minutes or until all the liquid has reduced.

By the end of the cooking time, the kombu should be dark, tender, and glazy, with very little to no liquid left.

If you still have some water left or the kelp is not as soft, keep cooking it for a little longer.

Once ready, tip in the toasted sesame seeds, mix well and set the kombu tsukudani aside to cool down.

kelp tsukudani cooked in a pot

Step 4

Now, let's make the onigiri rice.

Make sure you're using Japanese short-grain white rice, also called sushi rice.

Wash the rice in a pot of cold water, swirling it around and rubbing it with your fingers.

Then, drain it well and repeat two more times or until the water runs clear.

washed sushi rice

Step 5

You can cook the onigiri rice in a rice cooker, following the manufacturer's instructions, or over the hob.

For this second option, add the drained rice to a pot, followed by the remaining 400 mL of water and salt.

Cover with a tight-fitting lid and bring the water to a boil.

Once boiling, lower the heat to medium-low and simmer the rice for 8-10 minutes.

You must not open the lid or stir rice while it cooks, or it won't cook properly.

All the water should have been absorbed by the end of the cooking time. Now, take a peek, and if there's still some water left in the pot, cook the rice for a few more minutes.

Then, remove the pot from the heat and without removing the lid, let the rice finish cooking in its steam for 10 more minutes.

cooked sushi rice

Step 6

Once cooked, transfer the onigiri rice to a moistened tray, shallow pot or bowl (traditionally a bamboo rice bowl).

You can optionally add 1-2 spoonfuls of roasted sesame seeds for extra flavour and crunch.

Use a spatula or a wooden sushi paddle to "slice" the rice vertically and horizontally, separating the chunks rather than mixing them.

This way, you won't damage the rice or make it mushy.

Cover the rice with a damp towel or a lid so it won't get dry, and get ready to prepare the kombu onigiri balls.

 cooked sushi rice in a pot

Step 7

Don't let the rice go lukewarm or cold. Instead, you must shape the onigiri balls while the rice is still hot and sticky, as they will hold together better.

Before you start, submerge your hands in a bowl of cold water to avoid the rice sticking to your hands.

Optionally rub a pinch of salt over your palms to give the rice balls extra flavour.

Take a large handful of rice, compact it and slightly flatten it.

Then, press your thumb in the middle to make a pocket, and holding the rice in your palm, add in 1-2 teaspoons of the kombu tsukudani (1).

Then, cup your hand, fold the rice over the filling, and seal it into a tight ball (2).

onigiri rice filled with kombu
onigiri rice ball

Step 8

To shape the onigiri, flatten the rice ball in your palm — as if you are holding a taco shell.

Use your other hand's thumb, index and middle fingers to make the "corners" of the onigiri (1).

Press and rotate the onigiri in your hand until the onigiri rice ball looks like a triangle (2).

Try working as fast as you can — the longer you handle the onigiri, the higher the chances it might break or fall apart.

Shaping the onigiri can be tricky at first, but the more you practice, the easier it will get.

If you struggle, you can also use an onigiri plastic mould, available online; or wrap the rice ball tightly with cling film before shaping it into a triangle.

woman shaping onigiri
woman showing onigiri rice triangle

Step 9

Finally, cut each nori sheet into six strips with a knife or scissors.

Wrap the base of each kombu-stuffed onigiri with a strip of nori seaweed with the rough side facing the rice.

You can optionally top the rice balls with leftover kelp, a sprinkle of sesame seeds and chillies.

Let the onigiri chill slightly in the fridge and enjoy your delicious kelp tsukudani onigiri as a snack or in your lunch box!

onigiri rice balls wrapped with nori sheet


Keep leftover onigiri balls in the fridge for up to two days, wrapped in cling film. If the rice balls get too dry, you can use them to make these delicious grilled yaki onigiri.