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One should cover a pan while heating?

Cooking abounds with old sayings and proverbs, which are sometimes useful tips and sometimes myths. We learn or hear them somewhere, and often trust them completely, even when they're wrong.

I propose simply to verify them, to see whether they are real useful tips that we can use, or just ill-founded popular beliefs.

Of course I can't claim to be writing scientific facts here, just personal observations and what I understand them to mean.

The belief

"One should always cover a pan while heating, so that it boils faster".

In other words, if you heat water (or something else), it comes to the boil faster with a lid on the pan than without.

The approach

We are going to heat 1 litre of water in an uncovered pan and measure the time it takes to boil , then another litre in a covered pan, heated and measured in the same way.

Comparing these times will tell us if it is really necessary to cover the pan.

Let's check:

1 litre of water is measured and poured into a pan without the lid and put on the hob with a thermometer in it. Starting temperature of water (and room): 70°F (19°C).
The heat is switched on. The water reaches 210°F (100°C) in 9 minutes and 30 seconds.
to allow it to reach room temperature again. Another 1 litre water is put in the same pan covered with the same thermometer in it, on the same hob. Starting temperature of water (and room): 70°F (19°C).
The heat is switched on. The water reaches 210°F (100°C) in 9 minutes and 27 seconds.
The result is shown more clearly in the diagram: the temperature of the uncovered pan in red and that of the covered pan in green.

Results

The time difference is too small to be significant. It really doesn't matter whether the pan is covered or not.

So, "One should always cover a pan while heating, so that it boils faster." : False.

Last modified on: February 27^th 2015

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