Two rice balls using fermented mustard greens

Burong Mustasa Onigiri (Fermented Mustard Greens Rice Balls)

Onigiri is a life saver. 

When my husband and I traveled to Japan for the first time more than a decade ago, we knew we wanted to stay within budget on most days. While we sometimes splurged on a nice dinner, during the day we would just grab a quick bite in a konbini or gyudon-ya.

These rice balls were a convenient and budget-friendly snack that we could find in almost every convenience store and bento box, while exploring different neighborhoods and tourist attractions.

Onigiri was also one of our go-to breakfast foods for when we want to start sightseeing early. It’s filling and portable. You can eat it with your hands, and enjoy a variety because it has different kinds of filling. 

Use Japanese rice

Onigiri is made from steamed rice tossed with a bit of salt and your filling of choice. It is shaped into a triangle or flattened into a ball, then typically embraced by a sheet of salty nori. 

I tried to make onigiri before using dinorado and other types of rice we Pinoys typically cook with, but the result just isn’t the same. The stickiness and texture of the Japanese short grain lend itself best to shaping the onigiri and holding together nicely. 

Onigiri filling options

Unlike Mabi and Karla who are vegans, I’m an omni. Of the most common fillings of onigiri, I’ve always been partial to salted salmon (I usually just make do with leftovers), tuna mayo, and simple furikake (rice seasoning typically made from nori, sesame seeds, salt and sugar). 

Both my husband and son love onigiri, so every so often I would prepare some for our meals. Since I started fermenting vegetables back in 2020, Mabi has suggested using some fermented vegetables.

We zeroed in on burong mustasa. Preserved mustard greens are also used in Japanese onigiri. I recently made some following Starter Sisters recipe and the peppery bite of the mustard greens get tamed in fermentation, while giving it a sour and salty flavor that is a great contrast to the rice.   

Chopped burong mustasa
  • 1 ½ cups Japanese rice, freshly cooked
  • 2 tsp furikake
  • 2 to 3 tbsp Burong mustasa, chopped (recipe, here)
  • 1 Nori sheet, cut into strips
  • Bowl of drinking water
  • Sea salt 

1. Cook Japanese rice according to package directions, usually it’s 1 cup of uncooked rice to 1 ¼ cup of water. One cup of uncooked Japanese rice should produce around 3 cups of cooked rice.

2. Once the rice is cooked, transfer it to a bowl and fluff it to allow it to cool down a bit. It should still be warm when you handle it, but not hot enough that it will burn your hands.

3. Mix the furikake and chopped burong mustasa into the rice. 

4. Wet your hands in a bowl of water (this is very important so the rice won’t stick to your palm) and then dip your fingers in some salt and spread it on your palm. 

5. Scoop about ⅓ cup of rice into your hand. Press and mold it into a triangle. Be careful not to squeeze the rice too tightly that it falls apart. 

6. Once you’re happy with the shape, wrap the onigiri with nori. 

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