Japan’ s convenience stores often recommend warming up their rice balls, but is it worth the extra hassle?

Japan’s convenience store onigiri (rice balls) are just about the greatest grab-and-go snacks on the planet. According to their makers, though, there’s often a way to make them even better: warm them up.

At major convenience store chains, the onigiri are always stocked on refrigerated shelves. However, each chain also always has a number of varieties with packaging or signage saying that, for the best taste, you should warm them up in the microwave before eating. The vast majority of people ignore this advice, though, since onigiri generally taste great unwarmed too, but we couldn’t help wondering if a little time in the microwave would make a big difference, so we decided to find out.

Taste-testing duties fell to our Japanese-language reporter Snufkin, who procured a quartet of test subjects at 7-Eleven, all of which the chain recommends eating warmed. In order to eliminate any other potential variables, Snufkin cut each onigiri in half and warmed one half up in the microwave, so that she could ensure the most direct comparison possible.

Let’s take a look at her taste test notes.

1. Yakionigiri with soy sauce and broth (125 yen [US$0.85])

“Yakionigiri” refers to onigiri that are lightly grilled, and usually brushed with a soy-based glaze beforehand. On its own at room temperature, Snufkin found this example tasty. Maybe a touch on the strong side in terms of flavor intensity, but a perfectly good example of a yakionigiri.

The packaging recommends 20 seconds in the microwave, but since Snufkin wasn’t warming up the whole thing she adjusted that down just a bit to 15 seconds. Taking the warmed-up half out of the microwave and popping it into her mouth…

…oh, wow, this really did make a big difference! The change wasn’t so much in the flavor, though, but the texture. Warming up the onigiri had made the rice softer and stickier, in the sense that the individual grains felt more cohesively attached to one another. The warmth also seemed like a better match for the strong flavor she’d noticed at room temperature, though she could also now detect just a bit of acidity to the flavor of the soy sauce now.

2. Fried rice with egg, vegetable and soy sauce (130 yen)

Most onigiri are made with steamed white rice, but you can find fried rice versions too. Oftentimes fried rice onigiri are limited-time items with unique fillings or which were produced in collaboration with a popular Chinese restaurant chain, but this one is 7-Eleven’s standard fried rice rice ball and is available all the time. There’s nothing strange or paradigm shattering here, just a quick serving of fried rice in circular form. The only complaint Snufkin had was that, at room temperature, the rice was a little crumbly.

Se expected this one to become a lot more fragrant after 15 seconds in the microwave, but actually there was little difference in the strength of its aroma. Once again, though, heating the onigiri worked wonders for its texture, as the warmer grains held together better as she bit into the onigiri. Warming up the fried rice onigiri also helped disperse its oil more evenly, improving the consistency of the flavor. Overall, this is a definite improvement over room temperature.

3. Maitake okowa (146 yen)

Okowa is a mixture of sticky mochi rice and meat, vegetables, or, in this case, fungi. 7-Eleven’s maitake okowa onigiri are a personal favorite of Snufkin’s though surprisingly she’s never tried warming them up before this test.

At room temperature, the rice is fairly firm, which makes for kind of a grainy texture as you chew. But also as you chew, or at least as Snufkin chews, she’s filled with joy at how delicious the combination of maitake mushrooms and mochi rice is.

And when she heated it up…

…whoa, so chewy! Once more, heating the onigiri seemed to help the grains of rice fuse together. The pre and post-heating texture difference was the most pronounced with the maitake okowa, so much so that they almost felt like two different dishes to Snufkin. Ironically, though, the difference is so big that which is better is going to be a matter of personal taste, and while Snufkin liked both ways, she thinks she’ll be sticking to eating the maitake okowa at room temperature.

4. Grilled sausage (200 yen)

Though it’s not new to 7-Eleven, Snufkin had never tried the grilled sausage onigiri before this. This rice ball is in the heavyweight class, since aside from a slab of meat on top, it’s got mayonnaise in the center, so it’s the sort of thing to reach for when you’re feeling hungry enough that a regular onigiri won’t cut it.

At room temperature, it tastes great, with the sausage, mayo, and black pepper seasoning all firing up the taste buds. However, Snufkin wasn’t so crazy about how the mayo left her tongue feeling oily even after she’d swallowed her bite, and at this point couldn’t see herself buying this type again.

That problem went away when she warmed it up, though. Not only that, warming up the sausage onigiri brought all the tastes, the meat, mayo, pepper, and sauce, together, tying them into a delicious unity that was lacking when the rice ball was still cool. So not only is Snufin adding the sausage onigiri to her rice ball rotation, she’s always going to warm it up.

And last, for a little extra experimentation, Snufkin did a tasting of kombu (kelp) rice ball (130 yen).

7-Eleven doesn’t specifically recommend warming this type of rice ball up, as is the case for most of its onigiri. Theoretically, though, all rice balls were warm at some point, since the rice has to be warm enough during shaping for the ball to form, so waring any rice ball up should, at the very least, be an option, right?

At room temperature, the kelp has a sweetness to it, and the nori seaweed wrapping’s aroma serves as a nice contrast to make the rice seem even more flavorful.

And when she warmed it up…

…oops, this turned out to be a bad idea. Putting the rice ball in the microwave overheated the kombu at the core, which threw off the balance of the flavors and mad it hard to eat, too. It didn’t taste bad, but the overall eating experience was definitely better at room temperature.

So in the end, Snufkin concludes that warming your onigiri up really does make a difference, and often for the better, but that there’s probably a reason why convenience store chains recommend it for some types but are mum on the others. Still, it’s definitely worth giving it a try when the store suggests it, especially if you do like she did and try a half-and-half comparison to see which way you like best.

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