How to Caramelize Onions | Serious Eats

How to Caramelize Onions | Serious Eats


A time lapse of onions caramelizing in the pan, from raw to darkly caramelized

[Photographs: Vicky Wasik]

Here’s the trick to caramelizing onions: there is no trick. At least, I have yet to find a method that promises significantly faster results and still delivers a properly caramelized onion. Not baking soda, not a pressure cooker, and certainly not dumping a bunch of extra sugar on top. You have some latitude with the heat, using a higher flame to move things along more quickly, but it’s risky.

The idea of quick caramelized onions is an appealing one. It’s even an approach we’ve toyed with on Serious Eats in the past. But after further testing (and taking reader feedback to heart), I simply can’t recommend a single alternative to the real deal.

Caramelized onions are more than just a delicious allium preparation. They’re a message to our get-rich-quick, dinner-in-10, six-pack-while-you-sleep society. They’re telling us: GTFOH. We need to listen. Recipes that promise caramelized onions in 10, 15, or 25 minutes should be approached with extreme caution. Caramelized onions take time—at least half an hour, often closer to an hour, sometimes longer. There’s no good way to avoid that.

Here’s what you need to know to make them right, and what not to do.

What Are Caramelized Onions?

Caramelized onions are made by very slowly cooking onions so that they become meltingly soft, deeply browned throughout, and wonderfully sweet. The onions are usually sliced, but can also be diced or minced.

Two different browning reactions are at play in the process: caramelization, in which sugars break down into hundreds of new molecules (read Stella’s great piece on the science of caramel for more on that), and the Maillard reaction, in which proteins and sugars transform into an insane number of new flavor and aroma molecules. Together, caramelization and the Maillard reaction turn pungent raw onions into something so mild and sweet, it might well be dessert.

Here’s what caramelized onions are not: They’re not onions that have been sautéed over high heat so that they brown and char unevenly. Caramelized onions need time to gradually and evenly deepen in color, flavor, and sweetness, so that the finished result is consistent throughout, without any bitter notes from burned bits. And even if you do cook them slowly and evenly, caramelized onions shouldn’t be cooked until they’re so dark that an acrid flavor hangs over them. Those are caramelized onions you’ve accidentally burned.

The pictures in this article show caramelized onions at a variety of stages, and I took one batch in the images pretty far for illustrative purposes. But you don’t always have to cook your caramelized onions so dark. There’s often a good argument for stopping at a lighter shade of brown, depending on the dish. My recipe for French onion soup, for example, encourages a lighter degree of caramelization—an approach that’s backed up by the recipes of many famous French chefs.

Does Baking Soda Speed Up Caramelized Onions?

Caramelized onions, made with and without baking soda

The two samples on the left were free of baking soda, while the two sludge piles on the right were cooked with baking soda. (The two top sample were cooked with butter, while the two bottom ones were cooked with oil.)

Short answer, yes. Long answer, yes, but it’s disgusting.

Baking soda makes the onions more alkaline, which speeds up the browning reactions necessary for properly caramelized onions. But it also weakens the pectin that holds the onion’s cells together, turning what should be soft but distinct pieces of browned onion into a nauseating stew of pea-green mush. The flavor is off, too, with a chemical bitterness that’s just plain wrong.

In my testing, I found no amount of baking soda that was acceptable, no matter how little I added. Even the most minimal quantities ruined the batch.

Does Adding Sugar Improve Caramelized Onions?

If caramelization is what you want, it stands to reason that adding sugar might be a good idea. Right? More sugar, more caramel! This is another one of those misguided tricks, though—the onions already have more than enough sugar to get them to the super-sweet phase.

When onions caramelize, one of the main things that happens is the sucrose, or natural sugar hidden within their cells, is transformed into other, simpler forms of sugar, including glucose and fructose. Those sugars taste sweeter than sucrose, which accounts for the increase in sweetness as the onions caramelize.

Adding sugar to the pot merely adds more sucrose to the formula, and will yield more simple sugars as a result. It’s a lot like tossing more logs on a fire; what you’ll end up with is not necessarily a better fire, just a bigger one. Try to enhance the process with extra sugar, and all you’ll end up with are extra-sweet caramelized onions—I think way too sweet. You don’t need more sugar, you just need enough heat and time to let the sugar that’s already there do its thing.

Can I Make Caramelized Onions in the Oven?

Onions caramelized in an oven

Indeed you can! The oven can produce delicious caramelized onions, and it can do so without requiring quite as much attention from the cook. Start the onions on the stovetop until they’ve softened and released some of their liquid, then transfer them to a moderate 375°F (190°C) oven and let them cook in there, stirring occasionally, until they reach your desired results. This can take a very long time, possibly several hours.

The advantage of using the oven is that the onions brown more slowly, freeing you from the more constant stirring of the stovetop method and allowing you more time to take selfies for that perfect “Look at me, caramelized onions are HOT” Instagram post.

The disadvantages are the overall longer time (even if you’re a little less tied to the stove during it), and potentially less even results; I’ve found that onion residue is more likely to scorch on the sides of the pot or pan, for instance, risking slightly burnt flavors. I prefer to use the stovetop method, but if the oven appeals more, go for it.

What About a Pressure Cooker or Instant-Pot?

Instant Pot countertop pressure cooker

A pressure cooker is yet another avenue often used for quick caramelized onions. The science is there: browning reactions happen faster at higher pressure, such as inside a pressure cooker. And if you test it out, you’ll find that the science works. A pressure cooker can indeed speed up caramelized onions.

But there are some significant negatives to using one for caramelized onions. First, a pressure cooker is a black box—once you seal the lid, there’s no way to know what’s happening inside the pot. You have no way to look inside the pot to see how browned the onions are, nor whether anything in there is burning (you also have no way to stir it, though this can be solved by putting the onions inside another vessel, like a Mason jar, to keep them from direct contact with the hot surface of the pot).

An even bigger problem with a pressure cooker, though, is that it traps steam. That is, after all, how it builds up all that pressure. What this means is that once you open your cooker, your caramelized onions—assuming they’ve properly caramelized—are swimming in excess liquid. You then have to cook all that water off. By the time you factor in the setup, pressurization time, cooking time, depressurization time, and water-evaporation time, you haven’t really gained much.

Choosing Your Ingredients and Tools for Caramelized Onions

What’s the Best Cooking Fat for Caramelized Onions?

You can cook the onions in any fat you want—butter, various vegetable and nut oils, lard. Heck, you can use rendered foie gras fat if you want, it’d be freaking delicious. In terms of the more commonly available options, my favorite is butter. Because it contains milk solids, it kicks off the browning process more quickly than vegetable oils do, and it glazes the onions more beautifully. It’s also more flavorful than most neutral oils like vegetable, corn, and canola oil.

What Kind of Onions are Best for Caramelized Onions?

As with the fats, you can use any kind of onion. Red onions, yellow onions, white onions, shallots, and extra-sweet varieties like Vidalia onions are all great. I’ve found that each yields slightly different results, some sweeter, some more bitter. Often, I’ve gotten the best results by using a mixture of different onion varieties, though this is by no means a requirement.

In my past tests, I’ve recorded the following observations, in case they satisfy your curiosity:

  • Sweet onion: mellow and sweet, with a brightness right at the end.
  • Red onion: deeper flavor, with a slightly bitter edge and less sweetness.
  • Yellow onion: lots of bright flavor, very mild bitterness, and a sweetness backing it up.
  • Shallot: really good balance of sweetness, with both bright flavors and deep, rich ones, and just a hint of bitterness.

What’s the Best Pot or Pan for Caramelized Onions?

In my experience, cast iron and stainless steel pans produce the best caramelized onions. Nonstick pans and enameled cast iron work less well, slowing down the caramelization process unnecessarily.

The size of the pot or pan (and even whether it’s a pot or pan) will depend on the size of your batch. The larger the batch, the larger the cooking vessel you’ll want, and, likely, the higher the walls. That said, you generally want to opt for width over height, since the browning of the onions happens on the bottom of the pan, so the more bottom you have, the better. Sauté pans, which tend to be wide and broad but also have high vertical sides to contain the onions, are particularly well-suited to the task.

Caramelized Onions: Step by Step

Step 1: Get the Onions Going

Uncooked sliced onions in a pan

Add the fat of your choice to the cooking vessel, turn the heat to medium-high and add the onions. You don’t need to wait for the fat or pan to heat up before adding the onions—you actually want to ease the onions into the heat and reduce any risk of the too-quick browning that can happen when food is added to a pre-heated pan.

You’re starting out over higher heat because you want to get things going, but keep in mind that as the activity in the pan ramps up, you’ll have to keep turning the heat down to prevent scorching.

Step 2: Cover (Optional, But it Speeds Things Up)

Putting a lid on the pan to speed up caramelized onions

The first phase of the process is softening the onions so that they collapse into a tender mass while releasing a good deal of their liquid. If you cover the pan, you’ll trap steam, which will speed up their softening, heat them more quickly, and help release their liquid more quickly. Lift the lid a few times during this stage to give them a stir and make sure nothing is browning yet.

You don’t have to cover the pan if you don’t want to, it merely shaves some minutes off the total cooking time.

Step 3: Uncover and Stir

As soon as the onions have softened, remove the lid so that the steam can escape; you won’t have good browning in the presence of a lot of water, so it has to have a way to escape the pot.

Step 4: Stir and Scrape

Scraping up the browned bits on the bottom of a pan while caramelizing onions

Continue stirring and scraping the onions every minute or two, keeping an eye for signs of browning on the bottom of the pot. When the browning starts speeding up, it’s best to lower the heat to keep the transformation slow and even. You can, if you want, continue to work over higher heat, but you’ll need to be more attentive, stirring and scraping even more frequently, and being ready with water to deglaze at a moment’s notice (see the next step for more on that).

As the brown glaze (called the fond in French) builds up under the onions, scrape it up with your wooden spoon. You want to keep scraping it up and folding it back into the onions. It’s delicious.

Do this over and over as the onions gradually more brown.

Step 5: Deglaze If/When Necessary

Adding water to the pan of caramelized onions to prevent scorching

There may come a point where you can’t scrape up some of those browned bits, they’re just cooked on too hard (if you’re cooking over higher heat, this will definitely happen). To deal with this, pour a few tablespoons of water into the pan to deglaze it. The liquid will help you dissolve the stubborn fond and allow you to work it back into the mass of onions. The water you add will pretty quickly cook off and the bottom of the pot will start to brown again. Deglaze as often as necessary to prevent the onions from scorching.

Deglazing the pan with water while cooking over higher heat is one of the only ways to speed up caramelized onions without sacrificing too much quality. You can deglaze as much as necessary while keeping the flame higher to brown the onions faster; the key is to add the water every time the onions threaten to burn. It should go without saying that you run the risk of ruining your onions by cooking them over higher heat, so proceed with caution.

When they reach your desired level of caramelization, remove them from heat and season with salt. Good job, you caramelized onions, and you did it the best way—the only way.

Deeply caramelized onions

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