Tea aficionados will tell you that you should never heat the water in a microwave, because the resulting brew just doesn’t brew right.
The answer may be to add silver plating to your glass or cup – for function rather than style. But it’s complicated.
First, to the core of the problem, as explained by researchers from the University of Electronic Science & Technology of China in a paper in the journal AIP Advances.
A traditional stove heats a container from below through convection: as liquid toward the bottom warms, it becomes less dense and moves to the top, allowing a cooler section to contact the source. This results in a uniform temperature.
Inside a microwave, however, the heating source – an electric field – exists everywhere. The entire glass or cup also warms, and convection does not occur. The liquid at the top ends up being much hotter than the liquid at the bottom.
The answer, Baoqing Zeng and colleagues suggest, is to put silver plating along the rim of the glass to shield the effects of the microwave at the surface of the liquid.
The silver acts as a guide for the waves, they say, reducing the electric field at the top and effectively blocking the heating. This creates a convection process similar to traditional approaches, resulting in a more uniform temperature.
And before you panic about putting metal in a microwave, it’s apparently been done before with steam pots and rice cookers. It does, however, require “finely tuned geometry”.
“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,” says Zeng.
It won’t work with leftovers, though, because convection doesn’t occur in solids.
“For solids, there is no simple way to design a bowl or plate in order to achieve a much better heating result. We can change the field distribution, but the change is very small, so the improvement is limited.”
The group is considering other ways to improve non-uniformity in solid foods, but the methods are currently too expensive for practical use.