Tuna Mayo Onigiri

Tuna Mayo Onigiri (ツナマヨおにぎり)

Tuna Mayo Onigiri is a modern take on traditional Japanese rice balls stuffed with canned tuna seasoned with Japanese-style mayonnaise and soy sauce. The combo was first popularized by the Japanese convenience store chain 7-Eleven in the early 1980s. Over the past 40 years it has grown to become the most popular flavor of onigiri in Japan, surpassing more classic flavors like umeboshi (pickled plum) and tarako (cod roe).

Why This Recipe Works?

• Because the filling needs to season the rice around it, the filling should be well seasoned and on the salty side. The mixture of Japanese-style mayonnaise and soy sauce is what gives tuna mayo it’s trademark flavor. 
• Onigiri should stick together, but they are meant to be light and fluffy, so it’s essential not to over squeeze them, or they will turn into a dense, heavy ball of mochi. 
• Wrapping the Onigiri in herbs or nori helps mask any fishiness from the tuna. 

Ingredients for Tuna Mayo Onigiri

• Rice – to make good onigiri, you need to use good rice. I recommend using a Japanese variety of short-grain rice. That’s because short-grain rice has a higher ratio of amylopectin to amylose relative to medium-grain and long-grain rice. This is important because amylopectin has a branched structure that makes it sticky, helping the onigiri hold its shape. You should be aware that many brands of “Japanese rice” actually use Calrose, which is a medium-grain rice. 
• Tuna – Any canned tuna will work, but I like using chunk tuna (a misnomer because it’s more like mashed tuna) in oil. Be aware that canned tuna comes in a variety of sizes. I’ve calibrated this recipe to work with a small US-size can (85 grams) of tuna. 
• Mayonnaise – The key to giving this rice ball filling that Japanese taste is using Japanese mayonnaise. I used Kewpie brand. Compared to American mayo, it’s more tart and savory, and it has an eggier taste as well. 
• Soy Sauce – The other seasoning for the filling is soy sauce. This not only increases the amount of umami in the tuna mayo mixture, but it also makes it saltier, so the rice is adequately seasoned. 
• Wrapper – To smooth over any fishy notes in the tuna, I like to wrap my Tuna Mayo Onigiri with either wild sesame or green shiso leaves (both are varietals of perilla). If you can’t find these, or you want to do a more traditional onigiri, you can use two nori sheets that have been cut into 3 strips each. 

How to Make Tuna Mayo Onigiri

Wash and cook the rice either in the rice cooker or on the stove. If you are using new crop rice, reduce the amount of water slightly. See my sushi rice recipe for the proper way to wash and cook rice on the stovetop, but use the water proportion from this recipe. 

While you wait for the rice, you can prepare the tuna mayo filling by opening and draining the can of tuna and adding it to a bowl with the mayonnaise and soy sauce. Stir this together well until there are no big chunks of tuna remaining. 

You’ll also want to prepare a bowl of water to wet your hands with, and a bowl of salt to season the outside of the onigiri. 

After your rice is done cooking and steaming, use a spatula or rice paddle to fluff the rice using a folding  and cutting motion. Use a light touch, and be careful not to smash or break the individual grains of rice. 

The rice is going to be too hot to shape into a rice ball, so transfer it to a bowl and cover it with a damp towel until it’s still hot, but not so hot that you will burn yourself. This is important because the rice becomes more sticky and harder to shape as it cools, and you want to be able to shape it without squeezing and compacting it too much. 

Once the rice has cooled enough to handle, wet both hands by dunking them in the bowl of water you prepared. Dip your index finger in the bowl of salt. Don’t be shy here, as some of this is going to make its way onto the outside of your onigiri to season it. Rub the salt between your hands to distribute it evenly. 

Cup one hand and scoop one-sixth of the rice into it. Poke a hole into the center of the mound of rice and scoop about two teaspoons of tuna mayo filling into the hole. 

Cover the filling up with the rice around the edges, and then fold your fingers over, so your hand forms a u-shape. Use two fingers from your other hand to create an upside-down v-shape and press it into the rice cupped hand.

Rotate the triangle onto another side and repeat the cupping and shaping to form an equilateral triangle (3 equal sides). Repeat until you’re happy with the shape, but be careful not to compress the rice too much, or your rice ball will be very dense and heavy. 

Wrap your Tuna Mayo Onigiri with a wild sesame leaf and repeat the process with the rest of the rice. 

Other Onigiri Recipes

• Umeboshi Onigiri (pickled plum)
• Nozawana Onigiri (pickled mustard greens)

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