Karashi Mentaiko Onigiri (Spicy Cod Roe Rice Ball) Recipe

Karashi Mentaiko Onigiri (Spicy Cod Roe Rice Ball) on a plate

The Spruce Eats / Qi Ai

Prep: 10 mins
Cook: 1 mins
Total: 11 mins
Serving: 1 serving
Nutrition Facts (per serving)
349 Calories
3g Fat
69g Carbs
10g Protein
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Nutrition Facts
Servings: 1
Amount per serving
Calories 349
% Daily Value*
Total Fat 3g 4%
Saturated Fat 1g 3%
Cholesterol 53mg 18%
Sodium 172mg 7%
Total Carbohydrate 69g 25%
Dietary Fiber 5g 19%
Total Sugars 0g
Protein 10g
Vitamin C 3mg 16%
Calcium 34mg 3%
Iron 2mg 9%
Potassium 272mg 6%
*The % Daily Value (DV) tells you how much a nutrient in a food serving contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.
(Nutrition information is calculated using an ingredient database and should be considered an estimate.)

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 chile 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 1/2 cups cooked short-grain Japanese brown rice

  • Kosher salt

  • 1/2 piece karashi mentaiko (spicy cod roe), about 1 to 1 1/2 inches long

  • 1 sheet seasoned dried seaweed (ajinori)

Steps to Make It

  1. Gather the ingredients.

    Karashi Mentaiko Onigiri (Spicy Cod Roe Rice Ball) ingredients

    The Spruce Eats / Qi Ai

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

    Wooden cutting board covered with plastic wrap

    The Spruce Eats / Qi Ai

  3. 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.

    Rice on top of the plastic wrap lined cutting board

    The Spruce Eats / Qi Ai

  4. 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.

    Karashi mentaiko in a bowl covered with plastic wrap

    The Spruce Eats / Qi Ai

  5. In the indented center of the rice, place a piece of cooked karashi mentaiko. 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. 

    Karashi mentaiko on top of rice, wrap the rice around the filling using the plastic wrap

    The Spruce Eats / Qi Ai

  6. 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.

    Karashi Mentaiko Onigiri (Spicy Cod Roe Rice Ball) formed using plastic wrap

    The Spruce Eats / Qi Ai

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

    Karashi Mentaiko Onigiri (Spicy Cod Roe Rice Ball) held by two hands

    The Spruce Eats / Qi Ai


  • This recipe assumes that the rice is freshly cooked. 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.
  • 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.

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