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Lots of recipes call for waiting for the water to come "to a boil." However I have never been sure when that is. From my viewpoint it could be at three different points:

  1. First start to see small air bubbles coming up from the bottom of the pan
  2. When the surface of the water is noticeably disturbed by the bubbles
  3. When it is a full on raging torrent of activity

Depending on the amount of water used, these three points could be several minutes apart from each other, which will affect the cooking time.

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If the recipe doesn't specify a temperature for the water, then I'd say either (1) the "boiling point" doesn't really matter very much, or, more likely, (2) the recipe was written poorly and you should find another ;-) –  ESultanik Jun 13 '11 at 17:15
There are very few cases where it really matters. As a rule of thumb, simmer when you don't want what you are cooking to be jostled around (poaching an egg), and use a rolling boil when you do (to keep pasta separated). Otherwise, don't worry. –  michael Jun 13 '11 at 18:45

3 Answers 3

up vote 22 down vote accepted

By definition, 1 is a simmer (once the bubbles form a steady stream), 2 is a boil, and 3 is a "roiling boil."

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So recipes are calling for #2 unless otherwise stated? –  Jack B Nimble Jun 13 '11 at 17:14
Yes, that is correct. –  BobMcGee Jun 13 '11 at 17:29
Remember that the "boiling point" (the temperature at which water boils) of water is significantly different based on altitude and mineral contents. Boiling an egg for 2 minutes in Colorado Springs yields a significantly different result than at the top of Pike's Peak. –  Cos Callis Jun 13 '11 at 17:55

One important note is that while bringing water to a boil, there is first a point where a bunch of little bubbles form on the bottom of the pot. These initial bubbles are dissolved air coming out of solution as the water heats. This is not the same as a simmer, The apparent difference between a simmer and air coming out of solution is that in a simmer, the bubbles will continually form and rise towards the surface instead of sitting on the bottom. The initial bubbles will occur at much lower temperatures, and long before the water simmers/boils.

So, to add to BobMcGee's answer, 0 is bubbles forming on the bottom - not a simmer, 1 - small bubbles rising towards the surface is a simmer, 2 is a boil, 3 is a rolling boil.

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Remember to use good judgement based on what you're actually cooking. Are the instructions to boil water for pasta, to add vinegar to water once it's boiling, or to heat something over the pot, for example? Even at 212 degrees Fahrenheit, most things you drop into boiling water will bring the temperature down dramatically. Sometimes this matters, and sometimes it doesn't. It depends on what you're making or trying to do with it!

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