How a Rolling Boil Is Different From Simmering

One day, our ancestors learned that fire creates heat—and we’ve been boiling water ever since. There’s no doubt about it: one of the most common recipe instructions is "bring a large pot of water to a rolling boil." We see it all the time, whether we’re cooking a pot of pasta or making a big batch of hearty soup. The characteristics that define what a rolling boil is can be a little murky. After all, the difference between a rolling boil and a full simmer comes down to a matter of a few degrees (and even that is a spectrum). 

If you cook consistently, you probably use a boiling or simmering technique most days without even realizing it. If you’ve never stopped to think about what characterizes a rolling boil, keep reading to learn more.

What Is a Rolling Boil?

By definition, the liquid should be consistently at 212 degrees Fahrenheit to be considered a rolling boil. Everything below that is considered a variety of a simmer—full simmers are just below a rolling boil. Gentle or barely simmering will produce random, soft, and small bubbles.

While there will be ebbs and flows as you add and remove ingredients, there are two things to look for when liquid is at a rolling boil. 

1. Large, vigorous bubbles: First of all, the bubbles should be big. When water simmers, that’s when you’ll see the smaller pockets that sporadically bubble. For a rolling boil, the bubbles should be large and forceful. 
2. Continuous bubbles on the surface: In reality, the liquid will be bubbling underneath the surface, too. But once the bubbles are consistently rolling across the surface of the pot, you’re good to go. 

Overall, you want that pot of liquid to look like a running bubble bath, with equally distributed large bubbles across the entire surface.

The Importance of a Rolling Boil In Cooking

So why do we turn to this technique so often? Keeping the water (or whatever liquid you’re using) at a continuous, rolling boil ensures that ingredients cook evenly without you having to fuss with them too much. You might need to stir the contents of the pot a few times, but otherwise, the movement of the liquid will do the bulk of the work for you. 

It’s also important to use if you won’t be boiling the whole time. Often, recipes will instruct you to bring something to a boil before reducing the heat to a simmer (think sauces that use starch to thicken them or one-pot rice dishes). This is because bringing the ingredients to a full rolling boil upfront sets everything in motion–the heat starts out evenly distributed. This will carry on as you continue cooking. 

A rolling boil is the ideal technique for certain methods of cooking. The most common are boiling pasta, grains, and legumes and blanching vegetables. Each of these benefits from the even cooking that boiling provides.

How to Achieve a Rolling Boil

There are essentially only two things you have to consider when you’re bringing liquid to a rolling boil. First, you want to wait until the bubbles become large and continuously burst across the whole surface of the pot. Once that happens, you’ll want to maintain the temperature of the water at 212 degrees. You can use a deep-fry or meat thermometer to register the temperature of the water so you have a good idea of what it’s supposed to look like. Once you have an eye for it, you don’t need to check the temperature every time.

Maintaining a Rolling Boil

The next step is maintaining a consistent heat level so the liquid will remain at a rolling boil even after you add other ingredients, such as pasta, grains, or vegetables. Use these tips to nail it every time:

• Use the right size pot: The pot or saucepan should be large enough that whatever ingredients you’re adding will fit comfortably. If the pot is too small, the water bubbles won't have room to keep moving around. When in doubt, aim for a size larger than you think you need. 
• Don’t overcrowd the pot: Similarly to when you’re frying something in hot oil, you want to work in batches so you don’t overcrowd the pot. Overcrowding ingredients makes them cook unevenly. It also takes longer for them to cook through. 
• Keep an eye on the heat levels: Don’t be afraid to adjust the heat level as needed to keep the liquid moving consistently. As you add ingredients to the pot, you might need to increase the heat since the temperature of the ingredients will lower the overall temperature of the boiling liquid. Likewise, if you're boiling several things in batches, you should return the liquid to a rolling boil before proceeding.

Recipes That Use a Rolling Boil

As one of the most common stovetop cooking techniques, we use a rolling boil without a second thought almost every day. Some recipes will instruct you to maintain a rolling boil when cooking certain ingredients like pasta, gnocchi, grains, lentils, dried beans, and potatoes (which can be used for mashed potatoes or potato salad). The same goes for blanching vegetables—any and all vegetables will cook evenly when they are consistently cooking at a boil. 

Other recipes start off at a rolling boil before being reduced to a simmer. This includes dishes like soup, stew, chili, and some sauces like marinara and barbecue. 

You can even use a rolling boil to peel fresh tomatoes. They only need 30 to 60 seconds in boiling water for the skins to begin to split open, making them easy to peel off. 

Hard-boiled eggs can't be made without starting with boiling (or at least simmering) water. Most techniques bring the water to temperature before turning it off, adding the eggs, and letting them cook with the residual heat.