7 Common Mistakes When Caramelizing Onions


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When I was younger, I actually thought that caramelized onions were a sort of allium-infused dessert. Needless to say, I wanted nothing to do with this bizarre-sounding foodstuff.

Luckily, it didn’t take too long for someone to set me straight by serving me a most delicious French onion soup, which is perhaps one of the most famous caramelized onion dishes. I could taste how the slow cooking had brought out a subtle sweetness and a soft texture in the onions, which made them perfect for absorbing the beefy broth. While caramelizing makes the onions sweeter, they’re still far from dessert.

When made well, caramelized onions add an inimitable flavor to any dish they touch, from omelettes to burgers to soup and beyond. When made poorly, they can be abrasive and too-pungent. Here, we’ll discuss what makes great caramelized onions–and how to attain the perfect batch at home.

What does it mean to “caramelize onions”? While most people think of onions first and foremost as being pungent, they’re actually fairly naturally sweet. There are many types of onions; all of them are appropriate for caramelizing.

Typically, to make caramelized onions, you cook the onions slowly, over low or medium-low heat, with some sort of fat: butter, oil, or a combination. During the cooking process, the natural sugars in the onions (there is not actually any added sugar) caramelize, releasing an intense flavor and rendering the onions to a soft consistency with a shimmering, translucent finish and a deep brown hue.


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7 Common mistakes when caramelizing onions. When caramelized onions go wrong, it’s usually due to one of these common mistakes. We’ll discuss each error, and how to remedy it so that you can have delicious results.

  1. You don’t deglaze the pan. To “deglaze” is to add liquid to the pan, which will help release the browned bits of whatever you’re cooking from the bottom of the pan. In this case, it’s the charred and browned bits of onion which are closest to the heat source on the bottom of the pan.

If you don’t deglaze your pan, not only do you lose out on the onion bits that get stuck to the bottom of the pan, but you also miss out on an opportunity to add more flavor to the caramelized onions.

Deglaze the pan with a liquid that will be harmonious with the finished dish to which you’ll be adding the caramelized onions. For instance, if you’re making a French onion soup, you could deglaze the pan with beef stock. If you’re making burgers for the big game, try deglazing the pan with beer.

The onions will absorb the flavor of the liquid, and will have an even more concentrated flavor.


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  1. You slice the onions too thin or too thick. Your onions have to be sliced just right to make perfect caramelized onions. If they’re too thick, the outsides of the onions might get mushy before the middle is cooked through; if they’re too thin, they might burn too easily or cook before they have attained the right flavor.

Go for about ⅛ inch thick with your onion slices. This is enough mass to keep them from drying out, but not so much that they won’t cook fully. For best results, try to keep your slices consistent, as this will keep them cooking at an even rate.

  1. You only use butter to caramelize your onions. Butter makes most things better, but to make perfectly caramelized onions, you’ll need to bring in some supporting ingredients.

While butter imparts a fantastic flavor in your caramelized onions, it also has a very low smoke point, which means that it can scorch or burn over heat. This can make the onions take on a toasty-looking brown hue and give a false indication of doneness.

Adding some oil, which has a higher smoke point than butter, will help keep the mixture from scorching. Avoid extra virgin olive oil, which is sensitive to heat, in favor of light or refined olive oil.

In terms of quantity, a good starting point is to use about 2 tablespoons of fat (I use one tablespoon each of butter and olive oil) per 2 large onions worth of slices. You should be able to fully coat the bottom of the pan with the mixture. The onions shouldn’t be swimming in the fat, though–if you do that, you’re not caramelizing, you’re frying.


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  1. You try to speed up the process. Caramelizing onions is not a process to be rushed. Depending on the volume of onions, it can take anywhere from 30 minutes to an hour to slowly cook the onions to perfection.

If you find yourself tempted to hasten the process by cranking the heat, resist the urge. The slow cooking is what slowly brings out the sweetness of the onions and allows them to caramelize and soften. If you increase the heat, they could burn–or, they could brown on the exterior but retain a raw onion flavor on the inside. Definitely not the point of caramelized onions!

  1. You let the onions get mushy. The best advice to keep from ending up with mushy onions is to closely monitor the pot. Even though it takes quite a while to make caramelized onions, they can go from perfectly cooked to mushy in very little time. By keeping a close eye on the pot, you’ll be able to notice subtle changes in the onions.

First, the onions will become translucent and lightly yellowed. They will progress to a rich, dark brown, and will decrease dramatically in size. You’re looking for completely soft, but not so soft you could crush them with a fork. If you walk away from the pan, you may miss this transformation and let the onions progress to mushy.


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  1. You crowd the pan. Even though onions will reduce quite dramatically when caramelized, you don’t want to start with an overcrowded pan. For one thing, the onions won’t have even access to direct heat.

For another, the onions will release moisture which will rise, effectively steaming the onions on top of it. This will keep your onions from cooking evenly, and will make the process take far longer. It’s not worth it.

Spread the onions in an even layer on the bottom of your pan, but don’t have them stacked in a mound. This will help ensure that they cook fully and evenly.

  1. You don’t store them properly. Not using all of your caramelized onions at once? Freeze the leftovers. They keep for months, and they retain their flavor very well. Plus, they won’t impart an onion-y flavor on anything else, as they would in the fridge. The Kitchn offers several clever ways to store them, from pre-measured servings in muffin tins to storing them simply in freezer bags.


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You don’t have to be a fancy French chef to make great caramelized onions. Mastering the art of making perfectly caramelized onions is an invaluable addition to your cooking repertoire, and will bring flavor to all sorts of dishes, from soups to cheeseburgers. By learning the proper method, you’ll be ensured flavorful, perfectly textured results.

Have you ever made caramelized onions?

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