Karashi Mentaiko Onigiri (Spicy Cod Roe Rice Ball)

Onigiri (Rice Ball) with Karashi Mentaiko (Spicy Cod Roe) Filling Naho Yoshizawa/Aflow/Getty Images
Prep: 10 mins
Cook: 1 mins
Total: 11 mins
Serving: 1 serving

One of the most popular ways in which spicy cod roe, or karashi mentaiko, is enjoyed in Japanese cuisine, is as a filling for rice balls, otherwise known in Japanese as onigiri, or also known as omusubi or musubi.

Karashi mentaiko is seasoned tiny cod roe encased in a thin sac or membrane and spiced with red chili pepper such as togarashi. In addition to karashi mentaiko, variations of cod roe which may be substituted as fillings for this rice ball recipe are mentaiko and tarako. For additional information regarding tarako, mentaiko, and karashi mentaiko, and how this food is enjoyed, please read this article available on the Japanese food blog.

Karashi mentaiko may be enjoyed either raw or cooked. For the purpose of this recipe, it is best if the roe is cooked before using it as a filling for onigiri, especially if the rice ball will be carried around as a snack or in a bento (lunch box), and not eaten immediately. On the other hand, if the onigiri will be eaten immediately, by all means, try it with raw karashi mentaiko. It’s a favorite of mine, and delicious!


  • 1 to 1 1/2 cups cooked short-grain Japanese brown rice (or short-grain white rice)
  • dash of salt
  • 1/2 piece of karashi mentaiko (spicy cod roe) (or approximately 1 to 1 1/2 inch length piece)
  • 1 large piece of
  • ajinori (roasted seaweed), or 2 smaller pieces
  • plastic wrap

Steps to Make It

  1. This recipe assumes that cooked, steamed rice is available. If you are using leftover rice, reheat the rice in the microwave until warm. The rice is easiest to mold into a rice ball and hold its shape when it is slightly warm.

  2. When making onigiri (rice balls), using plastic wrap helps to contain the rice and in some ways makes it easier to mold the rice into a triangular shaped rice ball. It also minimizes any mess.

  3. Cut a medium sized piece of plastic wrap and lay it flat on a clean cutting board. Gently sprinkle the plastic wrap with salt. This step is optional, but the additional salt on the exterior of the onigiri is very common. 

  4. Scoop warm cooked rice onto the center of the plastic wrap in a heaping pile. Slightly flatten out and spread the rice so that you can easily imprint a thumb into the center of the rice. The technique is similar to making thumbprint cookies.

  5. Cook the karashi mentaiko by placing it in a small bowl and covering it with plastic wrap, then microwaving it on high for 10 to 15 seconds or until cooked through. The mentaiko will change in color from a deep, translucent pinkish-red to a pale, solid light pink color.

  6. In the indented center of the rice all, place a piece of cooked karashi mentaiko. Or, use raw cod roe if you prefer. Next, take the ends of the plastic wrap and slowly bring the ends of the plastic wrap together as the rice encloses the karashi mentaiko filling. 

  7. The onigiri will form a shape resembling a round ball. Next, gently squeeze the onigiri in your hands by cupping your hands together. Gently rotate the onigiri in the triangular-cupped shape of your hands, while gently flattening the center at the same time by pressing your fingers into the rice ball. You’ll achieve a thick, yet almost flat triangular shape.

  8. Unwrap the plastic wrap from the onigiri. Use the dried seaweed sheet to wrap the onigiri. Enjoy immediately or wrap in a clean sheet of plastic wrap to pack in a bento or lunch.

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