One YouTube viewer told me they ate a mentaiko mayo onigiri at a convenience store in Japan and still cannot forget it. They asked me to make it.
Challenge accepted. In that spirit, I made this mentaiko mayo onigiri. The mayonnaise comes first, soft and mellow, then the mentaiko grains and the heat push through. That convenience store rice ball was my target.
Mentaiko mayo onigiri
Recipe Snapshot
- What is it? A Japanese rice ball with chili-cured mentaiko, loosened with mayonnaise, tucked in the middle and wrapped in nori.
- Flavor profile: Creamy, mellow mayonnaise comes first. Bite down and the roe grains come apart, the chili heat close behind, and dashi umami lingers on your tongue at the end.
- Why this recipe works: Just a pinch of dashi granules gives the filling a junky, store-bought kind of umami. Chili-cured mentaiko in place of salt-only tarako keeps the heat alive through the mellow mayonnaise.
- How to make it: Scrape out the roe, mix in the seasonings and tuck it into the center of warm rice. No heat or special tools, and a mold lets anyone shape them evenly.
- What to expect: With cooked rice ready, the whole thing takes about 10 minutes. The only hold-up is a runny filling, and a short chill firms it up so it wraps easily.
What Is Mentaiko Mayo Onigiri?
Mentaiko mayo onigiri is a Japanese rice ball filling. You loosen the mentaiko, mix it with mayonnaise, and wrap that in the center of the rice. Plain mentaiko onigiri, with no mayonnaise, are just as common in Japan. The mayonnaise is there to soften the salt and the heat, and both versions are standard.
The name mentaiko comes from a Korean word for Alaska pollock. Around 1907, pickled Alaska pollock roe was traveling from Busan to Japan. The original form was roe coated with chili pepper. After the war, Fukuya set out to sell it in Hakata. They launched it in 1949, it did not sell, and they adjusted the amount of chili and the curing method again and again until the flavor settled. They taught that method to the shops around them, and Hakata mentaiko became an industry rather than one shop’s product. Eventually, mentaiko spread into everyday fillings for onigiri and pasta.
English packaging says spicy cod roe, but the roe inside comes from Alaska pollock. Mentaiko is also called karashi mentaiko, and here karashi means chili pepper. It has nothing to do with mustard. The same roe cured with salt alone (no chili) is tarako. In Hakata and Shimonoseki, mentaiko can mean the salt cure with no chili heat, and only the spicy one is called karashi mentaiko.
Mentaiko Onigiri Ingredients
- Mentaiko (spicy pollock roe): It carries the salt, the chili heat and the soft little grains you feel in every bite. The chili in its cure is where the heat comes from, which is why this recipe calls for mentaiko over plain salted tarako. Outside Japan it can be sold chilled or frozen, and you will find it in the seafood case at an Asian grocer. If yours comes frozen, use it half-thawed.
- Japanese mayonnaise: Japanese mayonnaise (Kewpie) is what rounds off the salt and heat of the mentaiko and turns them mellow. Stick with the amount on the recipe card, because the whole filling is balanced around it.
- Japanese short-grain rice: Use it while it is still warm. The starch on the surface of the grains is what glues them together and holds the triangle. In the US, you can find California-grown short-grain rice such as Tamaki Gold or Tamanishiki.
Substitutions & How to Customize
Here are the swaps for anything you cannot find, closest first, and a few small ways to make the filling your own.
Substitutions:
- Mentaiko → Tarako: If heat is not your thing, this is the closest swap. Tarako is the same pollock roe cured in salt alone, so the grains stay and only the heat goes. If you just cannot find mentaiko, a pinch of ichimi togarashi (Japanese chili powder) or gochugaru (Korean chili flakes) mixed in brings tarako close to it.
- Mentaiko → Myeongnan-jeot: The next closest after tarako, sold at Korean grocers. This Korean pollock roe is saltier than mentaiko and smells more strongly fermented, so go lighter on the salt for your hands.
- Japanese mayonnaise → Regular mayonnaise: The quick fix when Kewpie is out of reach. A few drops of rice vinegar and a tiny pinch of sugar bring it a little closer. The filling already has dashi granules in it, so there is no need to add dashi.
- Japanese mayonnaise → Homemade Japanese-style mayonnaise: If you have the time, you can make Japanese-style mayonnaise from scratch. I have a recipe for it.
- Japanese short-grain rice → Korean rice: When you cannot find Japanese rice, Korean rice is the closest. Its texture and flavor are very much like Japanese rice.
Substitutions that I don’t recommend:
- Ikura instead of mentaiko: These salmon eggs are bigger and oilier and burst in your mouth, so you end up with a different filling altogether.
- Mentaiko pasta sauce instead of mentaiko: It is already loosened with cream or oil, so it will not stay put inside the rice.
- Jasmine or other long-grain rice instead of Japanese short-grain rice: The grains will not stick together, so you cannot press them into a triangle. Never use it for onigiri!
Have trouble finding Japanese ingredients? Check out my ultimate guide to Japanese ingredient substitutes!
How to Customize:
- Butter: If you want less heat, mix in a little unsalted butter. Its fat rounds off the heat, the same way the mayonnaise does.
- Shiso or white sesame seeds: Stir in chopped shiso leaves or white sesame seeds for a different aroma.
- Cream cheese: Mentaiko mayo with cream cheese folded in is a popular twist, sold in shops and made at home.
How to Make My Mentaiko Mayo Onigiri
To make this recipe, an onigiri mold can be used (optional).
i. Lay the mentaiko on a cutting board and cut a slit lengthwise through the thin skin with scissors or a knife.
ii. Open it up and scrape the roe out with a spoon.
You can eat the skin or throw it away. I like to enjoy it as a nice little snack while I cook.
i. Move the roe to a bowl and add the mayonnaise, soy sauce and dashi granules.
ii. Mix until everything is evenly blended, and stop while some of the grains still hold their shape.
If the filling turns out runny, give it a short rest in the fridge before it goes into the rice.
Overmix and you end up with a pink sauce where you cannot feel a single grain. Leave the grains dotted through the mayonnaise, and they come apart in your mouth as you eat.
i. Divide the rice into 6 portions.
ii. If you are shaping by hand, wet your hands with cold water, then rub a little salt over your palms.
iii. If you are using a mold, sprinkle a pinch of salt into it.
Salt on your hands seasons only the surface of the rice, and it lifts both the lightly sweet rice and the mellow filling. The filling already carries salt from the mentaiko and the soy sauce, so salt mixed into the rice itself makes the whole thing too salty.
i. By hand, put 1 portion of rice on your palm, spread it flat, and press a hollow into the center.
ii. With a mold, spread half of 1 portion over the bottom of the mold and press a hollow into the center with your finger.
iii. Spoon the filling into the hollow.
Keep the filling in a small, tight mound right in the center rather than spreading it out.
i. By hand, fold the rice over to enclose the filling, then press and turn until you have a triangle with rounded corners.
ii. With a mold, cover the filling with the other half of the rice and sprinkle on a pinch of salt. Press the lid down firmly to set the shape, then lift the onigiri out of the mold.
Instead of wetting your hands, you can also wrap the rice in salted plastic wrap and shape it through the wrap. The pink of the mentaiko stays off your hands.
3 quick presses set the shape better than pressing over and over. Your dominant hand forms 2 sides of the triangle, then you turn the rice and form the third. Keep squeezing hard and the pocket of filling bursts while the rice packs down tight. If the seam stays closed as you turn it, the filling is sealed in.
i. Wrap the nori around the onigiri just before you eat.
Wrap it early and the steam from the rice leaves the nori soft and limp.
Tips for the Best Mentaiko Rice Balls
- Go easy on the filling and keep it in the center. The more filling you put in, the thinner the wall of rice around it gets. A thin wall cracks as you shape the rice ball, and the mentaiko mayo squeezes out through the seam. Keep a lighter amount gathered in one lump, and the rice closes over it properly.
- Taste a little of the mentaiko first to check its salt. How salty mentaiko is changes with the shop and the brand. If yours is on the salty side, go lighter on the salt you rub on your hands.
- Use freshly cooked rice, still warm but no longer steaming hard. Rice that has gone cold turns into a lump of clay unless you warm it up again. When the grains look glossy, stand apart from each other and feel a little tacky, the rice is ready for your hands.
- If the filling looks loose, chill it before it goes into the rice. A loose filling gets pushed out of the rice by the pressure of your hands. Cold firms up the mayonnaise, and the filling holds its place in the middle.
Set a little of that chilled, firmed-up filling in the middle of warm rice, and the mentaiko mayo stays tucked inside until the very last bite.
Storage & Meal Prep
Fridge: Cool, wrap each in plastic without nori, and chill overnight. Firm rice has not spoiled.
Freezer: Not recommended. Frozen mayonnaise splits and thaws watery.
Meal prep: Make the filling the night before (it keeps 1-2 days chilled) and cook rice on shaping day. Add an ice pack to bento, and in summer keep it out 1-2 hours at most.
Reheating: Microwave briefly with the wrap ajar, then add nori.
What to Serve With Mentaiko Mayo Onigiri
- Homemade Miso Soup
- Dashimaki Tamago (Rolled Omelette)
- Easy Takuan (Pickled Daikon)
- Spinach Ohitashi
Spicy Cod Roe Onigiri Troubleshooting
The filling has gone loose, from the amount of mayonnaise or from water in the mentaiko. Squeezing the ball harder to hold it in only pushes more of it out. Chill the rest of the filling in the fridge to firm it up, and if it is still loose, fold in a little more scraped-out roe before you wrap it.
Too much filling, or filling spread out flat, leaves the rice around it stretched too thin. For a ball that has already split, take out a little filling, gather the rest back into the center, add a bit more rice and wrap it up again.
Either the rice was cooked with too much water and the mayonnaise adds its oil on top, or pressing hard while shaping has crushed the grains. For balls already shaped, sear the outside in a frying pan to make yaki onigiri (grilled rice balls), and the toasty crust covers the stickiness. Next time, cook the rice with a little less water and set the shape with 3 light presses.
More Japanese Copycat Recipes
If another store-bought taste from Japan is stuck in your head, my Japanese Copycat Recipes are where I chase the rest of them down.
Did You Try This Recipe?
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Mentaiko Mayo Onigiri
Ingredients
- 50 g spicy cod roe (mentaiko) half-thawed if frozen
- 3 tbsp Japanese mayonnaise Kewpie, or regular mayonnaise if you have none
- ¼ tsp Japanese soy sauce (koikuchi shoyu)
- ⅛ tsp dashi granules
- 700 g cooked Japanese short-grain rice about 100-120 g per rice ball, freshly cooked and still warm
- salt for shaping
- 6 strips roasted seaweed for sushi (nori)
The ingredient brands and tools I trust are in my Japanese pantry guide and my cooking tools guide.
Can’t find certain Japanese ingredients? See my substitution guide here.
Instructions
- Place 50 g spicy cod roe (mentaiko) on a cutting board and make an incision lengthways through the skin using scissors or a sharp knife. Open it up and scrape out the inside with a spoon.
- Transfer the mentaiko to a bowl (you can eat or discard the skin) and add 3 tbsp Japanese mayonnaise, ¼ tsp Japanese soy sauce (koikuchi shoyu) and ⅛ tsp dashi granules. Mix until evenly distributed.
- Divide 700 g cooked Japanese short-grain rice into 100-120 g portions. If shaping by hand, wet your hands and sprinkle them with salt. If using a mold, sprinkle the mold with a pinch of salt.
- To shape by hand, take a portion of rice and flatten it on your palm. Make a dent in the center and add about 2-3 tsp of the filling. If using a mold, fill it up just over halfway with rice and press a dent in the center before adding the filling.
- If shaping by hand, fold the rice over to seal the filling inside, then press and turn to shape into a rounded triangle. If using a mold, fill it to the top with rice and sprinkle another pinch of salt on top. Press the lid down firmly to shape, then remove it from the mold.
- Wrap with nori right before eating. Enjoy!
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