Science Questions

Why does soup in a microwave heat up faster around the edge?

Tue, 4th Oct 2011

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Question

Tony Bun asked:

When heating soup in a soup bowl on a microwave oven, the soup begins to heat rapidly on the perimeter of the bowl and remains lukewarm in the centre. Why?

Answer

Dave -  It might be something to do with a slight misconception of how microwaves cook.  People often say they cook from the inside out - they don't, strictly. Actually, microwaves are form of electromagnetic radiation, a form of light, and they're absorbed within the outside inch and a half or so of the food.  So, right in the centre, itís kind of insulated from the microwave by all the other food around it.  So the soup in the middle is going to be getting less heating than the soup on the outside.  Also, the soup on the outside is thinner so itís going to get heated from all directions.  The soup on the outside is essentially getting more microwaves than the soup in the middle, so it gets hotter.

Chris -  Thank you, Dave.  And what can I do to remedy the problem so that my soup is more evenly heated in the future?

Dave -  Take it out occasionally and give it a mix is your best bet.

Chris -  Iíll remember that.

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