If you’ve never had mentaiko onigiri before, you’re in for a treat! These Japanese rice balls are filled with mentaiko, a seasoned pollock roe that’s creamy, a little salty, with just the right amount of spice. Once it hits warm rice, it turns into this rich, almost buttery filling that’s seriously hard to stop eating.
I love how simple these are to make, but they still feel a bit special. A bit different, you know? The filling comes together in minutes, and once you shape everything into soft, fluffy rice, you’ve got something that feels comforting and a little indulgent at the same time.
They’re perfect for a quick lunch, an easy snack, or one of those meals where you want something satisfying without putting in a tonne of effort. If you’re into onigiri or just looking for a new way to enjoy rice, this one’s definitely worth trying.
What is Mentaiko?
Mentaiko is seasoned pollock roe, commonly used in Japanese cuisine. It’s cured with salt and often chilli, which gives it a savoury, slightly spicy flavour. The texture is soft and creamy, and when warmed, it almost melts into whatever you’re eating it with.
Mentaiko onigiri are Japanese rice balls filled with this rich, flavour-packed roe and shaped into soft triangles or rounds. The warm rice balances out the saltiness and spice, making each bite comforting and seriously moreish. You’ll often see them wrapped in nori or lightly grilled, and they’re a popular grab-and-go snack in Japan.
Personally, mentaiko is up there with my favourite onigiri fillings! Particularly in western culture, it’s an underrated ingredient and many people can be a bit unsure of it. But trust me, if you like tuna or salmon fillings (a slight fishiness), you will love mentaiko!
Why You’ll Love This Recipe
These mentaiko onigiri are simple to make, packed with flavour, and perfect when you want something a little different without a lot of effort. And if mentaiko sounds a bit unfamiliar, don’t worry. If you enjoy tuna, salmon, or anything a little briny and seafood-forward, you’ll likely love this.
- Big flavour, minimal effort – The mentaiko filling comes together quickly but delivers that rich, savoury, slightly spicy hit.
- Creamy and comforting – Warm rice and melty mentaiko is a combination that feels cosy and satisfying every time.
- Easy to customise – Keep it simple or add extras like kewpie mayo, butter, or a quick grill for crispy edges.
- Perfect for any time of day – Great as a quick lunch, snack, or even a light dinner when you want something low effort.
- A fun way to switch up rice – If you’re stuck in a rice rut, this is an easy way to make it feel a bit more exciting.
Ingredients & Substitutions
- Short grain rice – Essential for that sticky texture that holds the onigiri together. Sushi rice or Japanese short grain rice works best here.
- Water – A simple ratio keeps the grains soft and slightly sticky.
- Karashi mentaiko – Spicy seasoned pollock roe that brings all the flavour. You can usually find this at Japanese or Asian grocery stores, often in the freezer section. If you enjoy tuna or salmon, you’ll likely love this.
- Nori sheets – Adds texture and that classic onigiri flavour. Cut into strips for easy wrapping.
- Furikake – A Japanese rice seasoning that adds a little extra savoury, umami finish.
How to Make Mentaiko Onigiri
Step 1: Rinse the rice until the water runs mostly clear, then cook with water using your preferred method (rice cooker or stovetop). Once cooked, allow the rice to cool until warm but still easy to handle.
Step 2: Slice open the mentaiko sacs and gently scrape out the roe into a small bowl. Discard the membrane.
Step 3: Lightly wet your onigiri mould with water to prevent sticking. If shaping by hand, dampen your hands instead.
Step 4: Add a layer of rice to the base and press it up the sides to create a small well in the centre. Spoon in about ½–¾ tablespoon of mentaiko, then cover with more rice.
Step 5: Place the lid on the mould and press down firmly for about 10–15 seconds, until the onigiri holds its shape. Gently remove from the mould.
Step 6: Wrap each onigiri with a strip of nori. Dip the top part of the onigiri in furikake.
Tips for Perfect Mentaiko Onigiri
- Use warm, not hot rice – Rice that’s too hot will be hard to handle and can make the onigiri fall apart. Warm to room temperature is ideal for shaping.
- Wet your hands or mould – A light rinse with water prevents the rice from sticking and helps you shape smooth, clean onigiri.
- Don’t overfill – It’s tempting, but too much mentaiko will make the onigiri harder to seal and shape properly.
- Shape gently but firmly – Press just enough for the onigiri to hold together without compacting the rice too much. You want it to stay soft and fluffy.
- Wrap nori just before eating (if you prefer it crisp) – If wrapped ahead of time, the nori will soften. Some people love this, but if you want that crisp texture, keep it separate until serving.
Storage
- Store nori separately – Wrap just before eating to keep it crisp. If wrapped ahead of time, it will soften (still delicious, just a different texture).
- Best eaten fresh – These are at their best when the rice is soft and slightly warm.
- Refrigerate leftovers – Store in an airtight container in the fridge for up to 1 day.
- Bring back to room temperature before eating – Let the onigiri sit out for 15–20 minutes to soften the rice slightly.
FAQs
Can I make mentaiko onigiri without a mould?
Yes, absolutely. Just dampen your hands and gently shape the rice around the filling into a triangle or round shape. An onigiri mould makes things quicker and more uniform, but it’s not essential.
Where can I buy mentaiko in Australia?
You can usually find mentaiko at Japanese, Korean or general Asian grocery stores, often in the freezer section. Look for “karashi mentaiko,” which is the seasoned, slightly spicy version.
Can I use something else instead of mentaiko?
If you can’t find mentaiko, you can try fillings like tuna mayo, cooked salmon, or even tarako (plain salted pollock roe). The flavour will be different, but still delicious. I have plenty of onigiri/rice ball variations for you to try!
Why is my rice falling apart?
This usually happens if the rice is too cool, too dry, or not pressed firmly enough. Use freshly cooked rice that’s still slightly warm, and press gently but firmly so the onigiri holds its shape.
Can I make onigiri ahead of time?
You can, but they’re best eaten fresh. If making ahead, store in the fridge and bring back to room temperature before eating. Keep the nori separate until ready to serve.
More Onigiri & Rice Ball Recipes to Try
If you loved these mentaiko onigiri, here are a few more rice-based recipes to add to your rotation:
- California Onigiri – Inspired by the classic sushi roll, filled with imitation crab, avocado and cucumber for a fresh and familiar flavour.
- Spicy Salmon Onigiri – A creamy, slightly spicy filling that’s perfect if you’re a fan of salmon.
- Kimchi Tuna Rice Balls – Packed with bold, punchy flavours from kimchi and tuna for a savoury, umami-rich bite.
- Spam and Egg Rice Balls – A hearty, savoury option that’s great for a quick meal or snack.
📖 Recipe
Mentaiko Onigiri (Spicy Pollock Roe Rice Balls)
Ingredients
- 1½ cups (~280g) uncooked short grain rice, rinsed
- 1½ cups (375ml) water
- 5-6 (~80g) sacs karashi mentaiko
- 3 nori sheets cut into strips
- Furikake to serve
Instructions
- Rinse the rice until the water runs mostly clear, then cook with the water using your preferred method (rice cooker or stovetop). Once cooked, allow the rice to cool until warm but still easy to handle.
- Slice open the mentaiko sacs and gently scrape out the roe into a small bowl. Discard the membrane.
- Lightly wet your onigiri mould with water to prevent sticking. If shaping by hand, dampen your hands instead.
- Add a layer of rice to the base and press it up the sides to create a small well in the centre. Spoon in about ½–¾ tablespoon of mentaiko, then cover with more rice.
- Place the lid on the mould and press down firmly for about 10–15 seconds, until the onigiri holds its shape. Gently remove from the mould.
- Wrap each onigiri with a strip of nori dip the top in furikake, if using. Serve immediately.
Notes
- Best enjoyed fresh while the rice is still soft and slightly warm.
- You can shape these by hand if you don’t have a mould.
- Don’t overfill, or the onigiri may not seal properly.
- For crisp nori, wrap just before eating. If wrapped earlier, it will soften.
- If refrigerated, allow onigiri to sit at room temperature before eating to soften the rice.
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