More about onigiri: keeping them fresh and more

In a comment to my Onigiri Revisited post, Jennifer said:

I’ve made fresh onigiri a number of times and would love to be able to make it the night before and take into work with me the next day. How do I do that? (or am I out of luck?) The rice gets all hard and I’ve tried sprinkling water on it in the microwave, but then it falls apart. Suggestions? Do I need a special type of rice? How do I store it after it is made?

Onigiri really are better if made the morning of the day you're going to eat them. I remember my mom waking up very early in the morning to make onigiri when we had a school outing (which usually meant an obento lunch with onigiri).

That being said, you can make them the night before, but you need to take some measures. There are a few things you can do to have moist (but not wet) rice balls.

Tips for making moist-until-you-eat-them onigiri

  • Use Japanese medium-grain rice (uruchi-mai, or sushi rice) - other types of rice don't really stay moist enough. (Short grain mochi rice is a possibility, but they make for very glutinous and gooey rice balls.) See the Looking at rice post if you're not sure what rice is what.
  • Make sure you are making them with freshly cooked rice, that's still hot, not cooled. Don't make onigiri with room-temperature rice..it will not stick together well and will dry out fast. The cooked rice should be nicely moist and plump to start with.
  • Wrap them completely in plastic wrap before storing in the refrigerator. This keeps the moisture in and prevents the surface from drying out. (Wrapping them in nori would have a similar effect, but then the nori will turn out rather soggy. I prefer to wrap in plastic and bring the crispy nori along separately.) A typical refrigerator is as dry as a desert inside, so you have to protect the rice from that dry air.

Keeping onigiri fresh

Onigiri were developed as a portable meal. Salting the surface is not only done for flavor; the salt helps to preserve the freshness of the rice. So be sure not to skip the salt if you plan to eat the onigiri some time after you make them.

Traditional onigiri fillings tended to be salty had long keeping qualities. Umeboshi (pickled plum) in particular is purported to have antibacterial qualities, so were an ideal filling for rice balls that were to be carried for a long time by hot, sweaty travelers.

If it's only going to be a few hours until you eat the onigiri, AND you can keep them reasonably cool (in a dark place out of direct sunlight), AND you use enough salt on the surface, they can be kept at room temperature. If you think you'll be carrying them around for a very long time though, it's probably best to use umeboshi or another long keeping, salty filling, rather than something like tuna-mayo or Spam.

Nuke them

If you are bringing them somewhere where you have access to a microwave, you can also freeze them. Defrosting time depends on how many onigiri you have, how big they are, how powerful the microwave is, etc. but once you get the timing right you can get hot onigiri that taste like they were just made. Be sure to wrap them in microwave-ready plastic wrap in that case! I often make extra onigiri and tuck a few in the freezer as treats.

What to do with dried out onigiri?

If the surface has dried out a bit but the insides are still moist, you can turn them into yaki onigiri. But if they are further gone than that, you can turn them into ochazuke, rice with tea. Just heat up the onigiri in the microwave, or even better grill them a bit a la yaki onigiri to make them crispy, then proceed as described in the ochazuke recipe by pouring on hot tea with toppings. Delicious!

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