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How to boil water – yes, really

The most foolproof way to check the temperature of water is with an instant-read thermometer.  (Scott Suchman)
The most foolproof way to check the temperature of water is with an instant-read thermometer. (Scott Suchman)
By Becky Krystal Washington Post

We have tried to encourage everyone to get into the kitchen no matter their skill level. In our opinion, no question was too basic, no task too insignificant to ignore. I’ve talked about how to scramble eggs, how to wash dishes, how to reheat leftovers. On those kinds of topics, a few sarcastic (to put it nicely) comments were always lobbed my way. Many were along the lines of this: “What’s next? How to boil water?” (Also: How to toast bread? Not ruling that one out, either!)

My friends, the time has come. Today, I am here to talk about how to boil water. I’ll be the first to admit that I spent years not thinking about it all that much until I was making a batch of bagels. On a whim, I wanted to confirm whether my water was, in fact, boiling – an important step in this recipe that helps puff up the rounds and causes the starches in the dough to gel for that signature shiny exterior. I inserted my trusty instant-read thermometer in the water, and I was off … by at least 25 degrees.

Be it making bagels, heating water for tea, canning jam or any other number kitchen tasks, how – and if – you boil the water actually matters. It can be an issue of taste, quality and even safety But don’t just take my word for it.

“The boiling point of water is an important cooking landmark,” Harold McGee writes in “Keys to Good Cooking.” At that point, 212 F (stick a pin in this for later), the water is “hot enough to kill microbes, firm meats and fish, and soften vegetables.” (Most microbes can be killed off at 130 to 160 degrees F, he notes, but the boiling point is an even safer bet.) It’s also a temperature at which doughs and batters can set.

OK, so it matters, you’re thinking. Now all I have to do is set a pot on the stovetop. What else is there to know? Turns out, a bit more.

How it works. At its core, when water boils, you’re witnessing its conversion from a liquid (um, water) to gas (steam/vapor) state. In “The Food Lab,” J. Kenji López-Alt gives an easy to understand explanation. Most of the time, the atmospheric pressure is greater than the vapor pressure of the liquid, which keeps the water molecules in their place. When you add heat to the equation, that energy revs up the water molecules. Eventually, the pressure from the water molecules exceeds that of the air and, voilà, they start to escape in the form of steam. The bubbles you see are steam rising up to the top away from the hottest part of the pot.

Now, keeping that in mind, let’s travel above sea level, where the 212-degree baseline is established. At higher elevations, atmospheric pressure is lower, so, yup, it’s easier for those water molecules to make the leap. Therefore, water boils at a lower temperature. In “On Food and Cooking,” McGee says every 1,000 feet of altitude lowers the boiling point by about 2 F. That can cause food to cook slower and less thoroughly.

How to recognize it. The most foolproof way is to check the temperature with an instant-read thermometer. Of course, that assumes you have one, it’s properly calibrated (which can done by inserting it in … boiling water or an ice bath) and it’s functioning properly. But if you understand what boiling water looks like, you don’t even need that. Unfortunately, that’s where I, and I suspect many others, have gone wrong.

There are plenty of ways to describe the visual cues, with no limit to the creative poetry some people have used. You may have heard the term “rolling boil,” which is vigorous bubbling that cannot be stirred down, according to “The New Food Lover’s Companion” by Sharon Tyler Herbst and Ron Herbst.

The problem with a rolling boil is you risk a boil-over, so unless your recipe specifically calls for it, you can safely reduce the heat to tame the water. As McGee points out, a gently bubbling pot of boiling water is only slightly lower in temperature than a rolling boil. As long as you see a constant stream of large bubbles, you’re good to go.

Things get slightly fuzzier (fizzier?) as temperatures decrease. Which brings us to the simmer, the stage before boiling. In “Salt Fat Acid Heat,” Samin Nosrat says the definition of a simmer can vary from 180 to 205 F. “Look at the pot – is it barely bubbling like a just-poured glass of your favorite sparkling water, beer or champagne? If so, then cheers – it’s simmering.” Achieve a simmer by bringing the water to a boil and then quickly reducing the heat. “Since simmering water is gentler than boiling water, it won’t jostle delicate foods so much that they fall apart or agitate tougher foods so much that they overcook on the surface before cooking through completely,” Nosrat writes. It’s her preferred temperature for just about everything cooked in liquid.

Looking for a few more visual cues? López-Alt says at a simmer, “bubbles break the surface of the water regularly, and from all points – not just a few individual streams.” Bubbles may be about the size of a pearl, as described in “Modern Tea: A Fresh Look at an Ancient Beverage,” by Lisa Boalt Richardson.

Below a simmer, there’s, naturally, the subsimmer, which López-Alt deems from 170 to 195 F. You’ll see “a couple of streams of tiny, champagne-like bubbles rising from the bottom of the pot,” he says.

At 170 to 180 degrees, Boalt Richardson says bubbles may look like the size of a peppercorn. Lower than 170 degrees, López-Alt says, is “quivering,” where some bubbles may form along the bottom and sides of the pot (more on that below). They won’t reach the surface of the water but can cause it to move a bit.

How to speed it up. McGee says you can halve the time in which it takes a pot of water to boil by covering it. That prevents evaporation, which otherwise has a cooling effect on the water. Likewise, once you’ve reached a boil, you can leave a lid ajar to allow for some, but not too much, cooling without risking a boil-over.

If you’re merely boiling to soak or steep something (noodles, dried chiles or mushrooms), don’t forget about your stovetop or electric kettle, which are efficient at heating smaller amounts of water.

Timing may also depend on your equipment. Induction cooktops are marvels when it comes to the speed at which they can bring water to a boil. Some non-induction electric ranges also feature a fast boil feature. If you have a gas cooktop, using a bigger burner – the biggest that you can use without flames licking up the sides of the pot – can help, too. Cook’s Illustrated found that using a 4-inch vs. a 2¾-inch burner to heat a 6-inch saucepan with 11/2 quarts of water shaved 5 minutes off the time to bring it to a boil.

The pot you use is another variable. I almost always choose to boil water in my enameled cast-iron Dutch oven. You may have heard that cast iron is a poor conductor of heat. In this situation, that’s actually a good thing. Materials that are excellent conductors, such as copper and aluminum, are so conductive that they “quickly give up heat to the environment,” McGee says, into the air and not the water.

Poor conductors, which include ceramics and cast iron, are in turn better at retaining heat. The more heat kept in the pot, the more can go into getting those water molecules moving. A layer of enamel can assist in evening out the heat, too. Stainless steel is a poor conductor that also heats unevenly, but “clad” pans (such as the aptly named All-Clad) feature a core of more conductive materials, such as aluminum, to even out the heat and get you the best of both worlds in terms of heat retention and conductivity.

The timing of when you add salt to water will not alter how quickly it boils. Adding salt to water actually raises the boiling point, McGee says, because it competes with the water molecules for the absorption of energy. In theory, that means salted water takes longer to boil, but you need 1 ounce of salt per quart of water to raise the boiling point by 1 degree Fahrenheit – an unrealistic amount for everyday cooking.

López-Alt says not to be fooled by the appearance of bubbles when salt is added to simmering water, which is not a sign of boiling but rather a result of having a new spot for steam bubbles to form. It can happen on any place where there’s an irregularity in the water, including scratches on the inside of the pot, a phenomenon you might see early on in the process.

Don’t walk away. I know, I know, a watched pot never boils. The corollary: A boiling pot needs to be watched. Believe it or not, I’ve heard from readers who have destroyed cookware by letting water boil off completely on its own or while cooking something like rice or beans. I’ve also had plenty of experience with pots boiling over, particularly in our Food Lab, where the induction cooktop heats things up so fast.

Bottom line: Stay nearby, especially once the water comes close to or reaches the boiling point. You may find you need to adjust the heat to maintain a steady but not dangerously raucous boil.

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