One should always cover a pan while heating

A recipe from cooking-ez.com

Times:

Preparation	Resting	Cooking	Start to finish
2 min.	1 hour	20 min.	1 hour 20 min.

Step by step recipe

1	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).
2	The heat is switched on. The water reaches 210°F (100°C) in 9 minutes and 30 seconds.
3	The hob is left to cool for about one hour, 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).
4	The heat is switched on. The water reaches 210°F (100°C) in 9 minutes and 27 seconds.
5	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.

Remarks

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

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