Be careful microwaving water!!!

The Scenario: A man decided to have a quick cup of coffee. He places a cup of water in a microwave oven to heat it up (something he has done numerous times before). When the timer shut the oven off, he removed the cup from the oven. As he was about to add the coffee granules to the hot water, he noticed the water did not appear to
be boiling, but suddenly the water “blew up” into his face scalding him.
Why did this happen?

The water actually became “superheated.” Water boils at 100 degrees Celsius at normal atmospheric pressure but in a microwave oven it can be superheated without tell tale bubbles appearing. If a litre of water is superheated by only 1 degree, it is in an unstable state and can suddenly produce about 3 litres of steam while quickly returning to boiling point.
The following conditions promote this potentially dangerous event:- Using a container with a very smooth surface, such as an unscratched glass or glazed container; heating for too long; or quickly adding a substance such as coffee granules or even a spoon. Even a jarring action can cause it to “explode.”
How to avoid it:
• The best advice is not to heat water in a microwave oven. Use an electric jug or kettle or a saucepan on a stove.
• Before putting the water into the oven, insert a non-metal object with a surface that is not smooth. (e.g. a wooden stirrer).
• Use a container, the surface of which is at least a little scratched or not new.
• Do not heat for longer than the recommended time for the quantity of water used.
• Tap the outside of the container with a solid object while it is still in the microwave oven.
An explanation:

In a microwave oven, the water is usually hotter than the container, whereas parts of a kettle or saucepan are usually hotter than the water. Further, the surfaces of some containers used in microwave ovens may be very smooth, almost at a molecular scale, whereas this is not true for kettles or saucepans.
Microwave ovens heat the water directly: the microwaves pass through the container and the water, and the water itself absorbs energy from them. The container absorbs little energy directly. In a kettle or saucepan, the container itself (saucepan) or a heating element (some kettles) is hotter than the water. The hottest points cause a small amount of local superheating, boiling is initiated here, and this then stirs the water.

Received & published by Henry Sapiecha

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