Here's the Perfect Way to Caramelize Onions

Just kidding. There really isn’t a perfect way. Like anything in cooking, the perfect way to caramelize onions is the way that works for you.

Today, I’m going to focus more on the factors that impact the process than I am on the specific steps you should take. There are plenty of amazing recipes out there for caramelized onions like this one, this one, and this video. (If you aren’t familiar with caramelized onions, then I’d recommend checking out one of those recipes or the video first.)

I believe if you know the factors at play, you can be more thoughtful about how you caramelize them.

But first, an important question.☝️

Why Are Caramelized Onions So Delicious?

Browning. Browning is the key to flavor. When you cook the onion for an extended amount of time, it extracts the water and starts to change color. And changes in color signal changes in flavor. Onions release amino acids that react with sugar as they heat up. It’s this chemical reaction that creates wonderful flavors and changes in color.

And if you’ve tasted caramelized onions before, you’ve experienced this magic first hand. They aren’t just sweet. They’re nutty, intense, and almost meaty.

The Factors That Impact Your Perfect Caramelized Onions

Time & Attention

Caramelizing onions takes time and requires frequent stirring to prevent burning. So know going into it that it will be a labor of love. But it’s oh so worth it!

My biggest tip of this whole thing: don’t be in a rush. And don’t turn up the heat too high, thinking it will speed up the process. Because unless you’re constantly stirring and deglazing them (more on that in a bit), they’ll burn. Speaking from experience here. 😞

The Type of Onion

I promised to tell you the best type of onion for caramelizing last week. So here it is. Yellow onions are the best. At least that is what I think. 😄 They aren’t as one-noted in sweetness as other onions because they have a touch of bitterness that creates a depth of flavor.

But really you can caramelize any type of onion and have a fantastic result. Shallots, white, yellow, sweet, or even red will all do the trick. Daniel Gritzer over at Serious Eats even recommends using multiple types of onions to add complexity.

Cutting the Onion

We’ve talked about this people! How you cut an onion changes its flavor. 😉 But to be honest, how you cut an onion here won’t make a big difference in flavor. Normally, the finer you cut them, the more pungent the flavor. But that’s less of an issue here. The onions are cooked for so long, the heat and caramelization process tames all their bitter compounds, no matter how you cut them.

But here is where it does matter: texture.

If you slice the onion lengthwise, along the root, you’ll burst fewer cell walls. That keeps the onion intact as it cooks. You’ll get identifiable slices of onion at the end and a subtle crunch.

If you slice the onion crosswise or dice it, you’ll burst more cell walls. And that’s not a bad thing. It just means your onions won’t stay as intact as you cook them. You’ll get something softer and more spreadable.

I like slicing them lengthwise personally. I’m all about texture. 😋

Covering Your Onions

More often than not, a covered pot is an enemy of browning. And we want to maximize browning. So we should leave them uncovered for proper caramelization, right? Not necessarily. We also have to watch out for burning. And it’s too easy for part of the onion to burn while the rest is still trying to brown.

Putting a lid on will steam the onions and cook them more evenly. How? Steam cooks the onions at the top of your pile too. So even if they aren’t in direct contact with the bottom of the pan, they will start to sweat. And that sweating begins to release the water in all of the onions at the same time.

But here’s the key. We then need to get the steam and the water from the onions out of there. Otherwise, the onion won’t brown. Once you cook the onions with the lid on for about 20 minutes, take the lid off. That allows the water to cook off.

The Fond

What is fond? Only one of my favorite things in the kitchen. Fond is the browned bits stick to the bottom of your pan. And it’s full of flavor! So whether you’re making a pan sauce or a soup, you always want to hold on to it. #SaveTheFond

The same goes for caramelizing onions. As the onions cook, fond forms on the bottom of the pan. Make sure you scrape up the fond as you stir your onions! It will maximize the flavor!

This leads me to…

Use Water

Like I mentioned above, we want to get rid of all the water in the onions to allow for browning to take place. But once the onions do start to brown, water can be your best friend!

Adding water periodically into the pan while caramelizing your onions will prevent burning. If you start to notice some burnt bits, add a splash or two of water. How does it help? The water makes it easy to pick up and incorporate that flavorful fond stuck to the bottom of the pan. The fond is usually the first thing to burn.

Plus, as we talked about in the first part of this series, onions have a water-soluble flavor compound called MPP. And so using water helps bring out extra flavor. 😋

Baking Soda

Baking soda is an interesting one. Heat impacts the chemical reaction that causes browning. But so do bases. 🔊 So that’s why we need to turn up the volume of our music when caramelizing onions. Just kidding. 😉 Not that kind of base. I mean the ones on the pH scale. And baking soda is our secret weapon for making a dish more basic. That’s why you may find it in recipes for caramelized onions.

A sprinkle will increase the speed at which the onions break down and start to brown. Why? Most cell walls weaken in more basic environments (higher pH) and stay strong in acidic ones (lower pH). It’s especially important to remember when cooking dried beans.

So using baking soda will speed up the process. But you have to be careful. If you add too much, it will impact the flavor. Different recipes recommend anywhere from ⅛ to ¼ teaspoon per pound of onions (aka about 3 large onions).

Personally, I don’t use baking soda. Why? Even though it speeds up the process, I think it does its job too well. When you add baking soda, the onions start to turn to mush as they caramelize. Delicious mush. But something closer to jam. You lose out on those pretty slices of onion and that subtle texture when the onion stays intact.

Sugar

It seems to make sense that you should add sugar to caramelized onions. Caramel is in the name! And adding sugar will make your onions sweeter. So if sweetness is what you’re going for, do it my friends!

I personally don’t add any sugar to my onions. While I love sweetness as much as the next kid, the extra sugar makes the caramelized onions more one noted in my opinion. The sweetness can overpower other complex flavors like nuttiness and bitterness.

Finish with Acid

Here’s my last tip. When the onions are done, deglaze the pan with vinegar instead of water. Then cook off any remaining liquid. The acidity will add brightness to the sweet and rich onions. You’ll get a nuance and depth of flavor. I highly recommend it!

Where I learned this: Ruhlman’s Twenty by Michael Ruhlman and many great articles on the internet like this one from Serious Eats and this one from Cook’s Illustrated.