Why You Shouldn't Microwave Your Tea, According to Science

Kettle all the way.

The Brits are self-confessed tea addicts, and as such, nearly every British household has something many American homes don’t: an electric kettle. Of course, some Americans may fire back: “Why do I need a kettle when I can heat water in the microwave?” Well, here’s the answer: science.

A newly published study with a very complex title—“Multiphysics analysis for unusual heat convection in microwave heating liquid”—came to a very simple conclusion: Microwaves do not heat water evenly.

The gist is this: When heating water from the bottom—like with a kettle or on a stove—the warmer water rises, allowing the colder water to fall to the bottom, and this pattern of convection heats the water evenly. But microwaves don’t heat by convection; instead, the heating is volumetric. So, as the paper states, “The temperature of the top is always the highest in the liquid when heated by microwaves.”

Glass Mug with Tea Bag Brewing
Getty Images / EyeEm

Here’s another way to think of it: You know how when you heat up food in the microwave, you inevitably find that some parts are hotter than others? That happens when you heat water in the microwave, too. After heating a glass of water in the microwave for 90 second, researchers found that water in the top of the glass was about 20 degrees Fahrenheit hotter than the water at the bottom.

Admittedly, nowhere in the paper did the authors use the word “tea”—that angle was added by the American Institute of Physics, which published the study – but it’s easy to see why a non-uniformly heated cup of water wouldn’t be as good for making tea, or any beverage for that matter, as evenly heated water would be.

But microwaving water may soon be as good of a solution as heating it in a kettle none the less, because the researchers—based out of the University of Electronic Science and Technology of China (UESTC)—have also come up with a potential solution: a glass with specially designed silver plating along its rim.

This metal rim helps guide the waves “to control microwave heating and improve the temperature uniformity,” taking an over 14 degree Fahrenheit temperature difference between top and bottom of the glass and reducing it to under a single degree in their experiment.

Of course, metal in the microwave is usually said to be a no-no, but this method apparently has that covered as well. “After carefully designing the metal structure at the appropriate size, the metal edge, which is prone to ignition, is located at weak field strength, where it can completely avoid ignition, so it is still safe,” Baoqing Zeng, a professor of electronic science and engineering at UESTC and one of the paper’s authors, stated.

In other words: Soon enough, your microwave may be able to join the tea party.

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