Perfect Caramelised Onions made easy. Learn how to caramelise onions for burgers, tarts, and more using butter and oil.
Jump straight to:
Q: What's caramel made from?
A: Sugar.
Q: So, to caramelise something, you need sugar, right?
A: Exactly.
Q: Do onions contain sugar?
A: Absolutely—lots of it!
And from that (most possibly) fantasy conversation, the magic of caramelised onions begins!
But wait—how exactly do you get those golden, sweet, perfectly jammy onions we all love to pile on burgers, tarts, and more?
Not all caramelised onions are created equal, as one contestant on MasterChef Malta recently found out the hard way. We knew this season would be exciting, as discussed in a previous article.
So, let's talk about the caramelised onions issue, shall we?
The Science Behind Perfect Caramelised Onions
Caramelising onions might seem straightforward—just cook them slowly, right? But there's more to it than meets the eye. When onions are heated, their natural sugars break down and undergo the Maillard Reaction process.
What is the Maillard Reaction? This chemical reaction is the magic behind the deep, complex flavours that make caramelised onions far superior to simple sautéed ones.
The Maillard Reaction occurs when the sugars and amino acids in the onions react under heat, creating that signature browning and layers of flavour.
It's not just about sweetness; the reaction adds a savoury, umami depth that transforms onions into the star of any dish. Without this reaction, you'd miss out on the rich, caramel-like flavour that makes these onions irresistible.
Oil, Butter, or Neither?
To achieve this, you need more than patience; you need the right technique. The Maillard Reaction requires heat above 140°C, which is why oil or butter are essential.
These fats help prevent the onions from sticking and raise the temperature enough for the Maillard Reaction to work its magic. Without them, your onions would burn before they even have a chance to caramelise.
Cue the MasterChef Malta drama! Gozitan contestants Josmar and Francesco, had a heated moment over whether to use oil or butter for caramelising onions. Why?
Chef Letizia Vella was not impressed when Francesco (apparently under the instructions of team captain Josmar) opted for oil only.
Tensions rose like steam from a hot pan after Josmar refused to add butter—directly against the advice of a very well-known and respected Chef.
Butter or oil for caramelised onions? Let's sort this out.
You can caramelise onions with just oil, just butter, or a combination of the two. But each option leads to a slightly different result:
Oil Only: Oil is great because it has a higher smoke point than butter, meaning it can withstand higher temperatures without burning. This method keeps your onions cooking evenly, but you might miss that extra richness and flavour depth that butter brings. The texture is good, but the flavour might be a bit flat.
Butter Only: Butter adds a luxurious, slightly nutty flavour thanks to its milk solids, which also brown during cooking. However, butter burns at a lower temperature, so if you're not careful, you'll end up with burnt onions rather than beautifully caramelised ones.
Butter and Oil Combo: The best of both worlds! Oil prevents the butter from burning, while the butter adds richness and depth. This combo helps the onions cook more evenly, with better flavour, and keeps everything in balance—just like in life, right?
What are the Best Onions for Caramelisation?
When it comes to caramelising onions, yellow onions are your best bet. They strike the perfect balance between sweetness and savoury depth, which intensifies as they cook down.
Thanks to their higher sugar content, yellow onions develop that rich, golden-brown colour and the sweet, jammy texture we all love.
White onions are also an option, though they tend to have a sharper, more pungent flavour, resulting in a less sweet finish. For something different, you can try red onions, which offer a slightly tangier taste and a deep, reddish hue. However, they won’t caramelise to the same level of sweetness as yellow onions.
If you’re after a super-sweet version, sweet onions like Vidalia or Walla Walla are a great choice, but they contain more water, so they may take longer to reach that perfect caramelisation.
In short, if you want classic caramelised onions, yellow onions are your go-to!
Best Practices for Caramelising Onions
Let's settle it once and for all: the perfect caramelised onions require a bit of oil and butter. Here's our take on how to do it right:
Use the right pan: A heavy-bottomed skillet is your best friend. It distributes heat evenly and prevents hot spots, which can lead to uneven caramelisation.
Low and slow is the way to go: Patience is the key to caramelised onions. Cook them over low heat, stirring occasionally. They need time to release their sugars and slowly develop that deep colour and sweet flavour.
Oil and butter: Start with a tablespoon of oil to get the onions going, then add a tablespoon of butter to layer in that rich flavour. The oil keeps the butter from burning while giving you the perfect caramelisation.
Seasoning: Salt the onions early. This helps draw out moisture, speeding up the caramelisation process.
A pinch of sugar (optional): Some recipes call for a tiny pinch of sugar to help with caramelisation. This isn't necessary if you're patient, as onions have plenty of sugar, but it can give a little boost.
Don't rush it: The whole process can take 30–40 minutes for a small batch. The longer and slower you cook the onions, the deeper the flavour will be.
The Role of Butter: Why Did Chef Letizia Vella Insist?
Butter contributes flavour that oil alone just can't match. Chef Letizia Vella berated Francesco because she understood that while oil might technically get the job done, butter is what gives caramelised onions that mouth-watering richness.
You'll still get caramelised onions with just oil, but they won't have that buttery depth of flavour that takes them to the next level.
Recipe: Perfect Caramelised Onions
Ingredients:
3 large yellow onions, thinly sliced
1 tablespoon olive oil
1 tablespoon butter
Pinch of salt
Optional: pinch of sugar
Method:
Heat the olive oil in a heavy-bottomed pan over medium-low heat.
Add the sliced onions and sprinkle with salt. Stir to coat the onions in the oil.
Cook the onions, stirring occasionally, for about 10 minutes, until they soften.
Add the butter and cook on low heat for another 20–30 minutes, stirring occasionally, until the onions are a deep golden brown and sweet.
Optional: Add a pinch of sugar halfway through for extra sweetness.
Once caramelised, remove from heat and serve with burgers, hot dogs, or even on a goat's cheese tart.
Why You Need to Try Caramelised Onions
If you've ever wondered, "Are caramelised onions burnt?"—the answer is no, at least when done right. They should be rich brown, not black, and taste sweet, not bitter.
Caramelised onions bring an explosion of flavour to any dish. They're a game-changer, from burgers to hot dogs to tarts and even chutneys.
Imagine them on a tart with goat's cheese or stirred into some hummus for an unexpected twist.
Savour the Perfect Caramelisation Process!
So, butter or oil? In the case of caramelised onions, both win. For the perfect combination of flavour and texture, use them together and enjoy your sweet, savoury, golden perfection.
Chef Letizia Vella was right to insist on butter, though we're not too sure about butter only - Sorry, Chef!
Now, you can wow your friends and family with your batch of perfect caramelised onions.
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