Maybe this belongs under Chemistry, but if water cannot get hotter than 212 degrees at sea level before boiling, why do some recipes call for faster (rolling?) boils rather than a simmering boil?

Sometimes things other than water are heated/boiled, but I believe the same underlying principle would apply, although at a temperature other than 212.

At a simmer, only the water at the very bottom is at the boiling point. At a rolling boil, all of it is. With the increased movement of the water, heat also transfers faster to anything in it.

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Originally Posted by makdan

Maybe this belongs under Chemistry, but if water cannot get hotter than 212 degrees at sea level before boiling, why do some recipes call for faster (rolling?) boils rather than a simmering boil?

Sometimes things other than water are heated/boiled, but I believe the same underlying principle would apply, although at a temperature other than 212.

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Labman,

Makes sense. Thanks for this and the Avogadro's number answer.

Moved to Chemistry

A little corrrection to what labman has said, since the water is all at the same temperature when it is boiling, the fact that it's moving does not increase the rate of heat transfer as labman said, rate of heat transfer depends only on the temperature of the water and the temperature of what it's cooking.

The faster the water is moving, the smaller the temperature gradient.

You mean gradient through the water? Sure it keeps all the water at the same temperature. It prevents the food from cooling the water too much and lowering the gradient between the water and the food. But it doesn't increase the rate of heat transfer.