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Be Careful When Using Microwave Ovens

Late at night on a cold winter's evening, Julia, an exchange student, bumps into Haruo, her host father, while doing something in the kitchen.

Be Careful When Using Microwave Ovens

Haruo

Hello there Julia. What are you doing at this time of night?

Julia

Because it is so cold this evening, I thought I would warm myself up with some hot milk.

Haruo

That sounds like a good idea, I might ask for a mug myself. When warming the milk, however, please take care because overheating drinks when using a microwave oven can be rather dangerous.

Julia

Really?

Haruo

Yes, when heating up milk and coffee, sometimes a phenomenon occurs called toppustu (or explosive boiling) where the temperature of the fluid rises too quickly and it is literally blown out of the vessel it was placed in.

Julia

Toppustu?

Haruo

When using a microwave oven to heat drinks, sometimes the fluid within the heating vessel fails to appear heated despite having reached its boiling point. Instead, pockets of heat are retained unevenly inside the fluid in an “overheated state.” If this happens, when the vessel containing the heated fluid is disturbed, a flavoring agent added, or when some form of vibration or stimulation occurs, the fluid immediately reacts violently in that it erupts out of the vessel as an explosive boil occurs.

Julia

That sounds scary.

Haruo

Yes, and in actual fact incidents involving burns resulting from explosive boils are also increasing in number. Examples include cups of coffee heated in microwaves erupting the moment they are removed from the oven, or heated cups of soy milk spilling over the instant someone stirs them with a spoon.

Julia

How can this explosive boil phenomenon be prevented?

Haruo

When heating drinks such as coffee, milk and soy milk, etc., in microwave ovens, the important thing is that you do not heated more than need them. Moreover, you should not use automatic oven functions such as the “heating button.” If you believe you have overheated a drink, wait a couple of minutes before opening the oven door. You should also take care when heating thick foods such as miso soup, curries and stews, etc., in a microwave oven.

Julia

I see. Well I will certainly be careful setting the microwave timer to warm our drinks.

Haruo and Julia then continue their discussion over their mugs of hot milk.

Julia

What other things should we be careful of when using microwave ovens?

Haruo

You should be careful when heating oily foods such as fried chicken and other things that have been fried, etc. Care is also required when heating foods with a low moisture content or when heating small amounts of food, etc. Such are often overheated. There are even cases recorded of the overheating of such foods resulting in smoke, flames and full-on fires.

Julia

And trying to heat food that is still wrapped in aluminum foil or retort packaging is also totally unacceptable, isn’t it?

Haruo

That is correct. You need to pay close attention to what you are doing because during winter we have more opportunities to use microwave ovens to warm up food and drinks during the evenings.

Julia

And looking inside our microwave oven, I can see that it is rather dirty. I’ve heard that built-up grime from cooking oil and scraps of food can also result in smoke, flames and fire.

Haruo

That is correct. Leaving the oven in such a state is unacceptable.

Julia

Then leave it up to me! Tomorrow I will clean the oven.
■Tokyo Kurashi Web
Be careful of explosive boils when using microwave ovens!
http://www.shouhiseikatu.metro.tokyo.jp/attention/topputsu.html (in Japanese only)

Did you know that using microwave ovens in certain ways can be very dangerous?
http://www.shouhiseikatu.metro.tokyo.jp/anzen/test/densirange_press.html (in Japanese only)