The Thrifty Rice Cooker: Keep it warm? Or reheat?


We love our suihanki (炊飯器, electric rice cookers). But have you ever wondered whether it’s better to keep cooked rice warm using the ho-on (保温,”keep warm”) function, or shut the cooker off and reheat the rice as needed in the microwave? Which is more energy-efficient? I got the scoop on this from Energy Conservation Center, Japan.

Let’s say you set your rice cooker to prepare 3 cups (3-, 3合) to be ready at 6 pm. You consume half of the cooked rice when it’s done, and leave the rest in the rice cooker on “keep warm” so it’s ready when straggling family members roll in around 10 pm wanting dinner. Keeping the rice cooker on for those four hours uses up 300.60 Wh of electricity, and costs you about 6.6 yen. Alternatively, you could turn the rice cooker off and use the microwave to heat up the remainder of the rice (about three bowls). That would use 295.27 kH of electricity at a cost of about 6.5 yen. Ok, that’s only a marginal difference but multiplied over 365 days a year and millions of households, forgoing the “keep warm” function could help make a dent in our current energy shortage. As a bonus, rice that’s been reheated in the microwave tastes better than rice that’s kept warm in the rice cooker for hours. For more tips on electricity conservation, click here . Also, please see my April 21 column in The Japan Times. Below are answers to questions I didn’t have space to answer there:

Should I unplug my microwave oven when not in use? –J.Y.

It depends on your microwave. Mine is a very simple Samsung model made in 2000. It doesn’t have a clock or fancy electronics. To turn it on, you simply crank a dial and off it goes. I just tested it using my watt meter, and it doesn’t draw any electricity at all when plugged in but not running. If your microwave is as simple as mine, you can leave it plugged in all the time. It’s not sucking on the grid except when you’re actually zapping something. But if your microwave oven has a clock display and/or electronic controls, it’s using electricity even when not in use. It’s not much — probably 0.5 watts, but if you don’t use your microwave often by all means unplug it.

How about my mobile phone charger?

Unplug it. Most mobile phone chargers draw 0.5 watts of electricity. This is not a lot — leaving it in all year would probably cost you 100 yen in electricity — but if everyone leaves their chargers in all the time, it starts to add up to a lot in wasted power. Make it habit to pull the plug as soon as you’re finished charging.

Is it true that turning on and off of fluorescent lights uses more electricity than leaving them on? — H.F.

No. You should turn off both keikō (fluorescent) and hakunetsu (incandescent) lights when not needed, even if you are going to turn them back on a minute or two later. By the way, if your bulbs or light fixtures are dirty, clean them. You'll get more light for the electricity consumed.

What about my computer?

Your computer will become obsolete before you’re wear it out turning it off and on. You should turn it off when you aren’t using it for long periods of time. If you tend to walk away and come back a lot, as I do, you might set it to go automatically into “sleep” mode if you don’t do anything for say, 15 minutes or an hour. “Sleep” mode requires a constant but reduced use of power (my computer uses 6 watts). “Hibernate” uses less power but takes longer to come back online.

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