Maillard Reaction vs Caramelisation: What's the Difference?

The Maillard reaction happens when amino acids from protein react with sugars, while caramelisation happens when sugar breaks down by itself under heat. Both turn food brown and create new flavours, but Maillard browning tastes savoury, roasty and meaty, and caramelisation tastes sweet, buttery and slightly bitter. In real cooking they often happen side by side, which is why the two get mixed up so often.

Why do people confuse them?

Because they look almost identical. A seared scallop, a pot of brown onions and a pan of amber caramel all go from pale to golden to deep brown, and they all smell wonderful along the way. Food packaging and menus don't help: "caramelised" is used for practically anything that's been browned, from onions to pork belly.

The difference shows up when you look at the ingredients going into the reaction, and at the flavours that come out.

What's the key chemical difference?

It comes down to nitrogen.

Sugars are made of only carbon, hydrogen and oxygen. When sugar breaks down on its own during caramelisation, every new molecule it forms is built from those same three elements. That limits the flavours to a recognisable family: caramel, butterscotch, toffee, a little fruitiness and, as it darkens, bitterness.

Amino acids, the building blocks of protein, bring nitrogen and, in some cases, sulphur to the party. When they react with sugars in the Maillard reaction, they produce whole classes of molecules that caramelisation simply can't make, such as pyrazines (roasty, nutty, toasted) and sulphur-containing thiazoles and thiophenes (meaty, savoury). That's why bread crust, roasted coffee and seared beef taste so different from a spoonful of caramel sauce, even though they're all "brown."

Chef Fizz says: No nitrogen, no meaty flavour. Sugar alone can do sweet and toasty, but it needs protein for savoury.

How do the two compare side by side?

What actually happens when sugar caramelises?

Heat table sugar (sucrose) on its own and here's roughly what unfolds:

1. Breaking apart. Sucrose splits into its two halves, glucose and fructose.
2. Losing water. Those sugars shed water molecules and rearrange into reactive fragments.
3. Building flavour. The fragments form aroma molecules such as diacetyl (a buttery note also found in butter and popcorn), maltol (toasty, cotton-candy-like), and furans (nutty, caramel-like). Small amounts of acids form too, giving caramel a faint tang.
4. Building colour. Fragments link into larger brown polymers, given the wonderfully old-fashioned names caramelans, caramelens and caramelins, in roughly that order as colour deepens.

Different sugars caramelise at different temperatures. Fructose starts around 110°C (230°F), which is one reason honey and fruit brown so readily. Sucrose and glucose need closer to 160°C (320°F). There's an interesting twist here too: researchers at the University of Illinois found that sucrose doesn't truly melt at all. It decomposes, and if held long enough at temperatures well below its textbook melting point, it can slowly caramelise.

What do the stages look and taste like?

For a classic sugar caramel, these are useful markers:

• About 160°C (320°F): pale straw colour, mostly sweet with a hint of caramel.
• About 170°C (338°F): light amber, classic caramel aroma, good for sauces.
• About 180°C (355°F): deep amber, richer and slightly bitter, great for crème caramel and nut brittles.
• Above about 190°C (375°F): dark brown to black, acrid and burnt.

The jump from perfect to burnt happens fast, often in under a minute. Caramel can also go wrong in a completely different way, by crystallising into grainy lumps, which is explained in our guide to why caramel turns grainy. For more on caramelisation itself, see the glossary entry on caramelisation.

Want to test your eye for browning? The Cooking Scientist app has a lesson on Maillard vs caramel, with a mini game where you sort foods by the reaction that browns them.

Which reaction is browning my food?

A handy shortcut: if there's protein in it, the Maillard reaction is probably doing most of the work. Pure sugar is the main place where caramelisation runs solo.

Mostly Maillard

• Seared meat and fish. Plenty of amino acids, very little free sugar, so almost all the browning is Maillard.
• Brown butter. The fat doesn't brown at all. The milk solids, which are proteins and lactose, turn golden and nutty. See the glossary entry on brown butter.
• Dulce de leche. Despite tasting like caramel, it's milk proteins reacting with lactose and added sugar at gentle heat, below 100°C (212°F), over a couple of hours.
• Toast and bread crust. Flour proteins and sugars released by yeast and enzymes, with some caramelisation of surface sugars at the hottest spots.

Mostly caramelisation

• Caramel sauce, crème brûlée tops, spun sugar and pulled sugar. Pure or nearly pure sugar, heated hot.

Truly both

• Onions. Onions have both sugars and amino acids, so slow-cooked "caramelised" onions are actually browned mostly by the Maillard reaction, with real caramelisation contributing too. Our guide on why onions get sweet when cooked explains where the sweetness comes from.
• Toffee and butterscotch. Sugar caramelises while the milk solids in the butter and cream add Maillard notes.
• Roasted vegetables. Carrots, parsnips and sweet potatoes have natural sugars and some amino acids, so their edges brown by both reactions.
• Coffee and cocoa. Roasting runs both reactions at once, plus other forms of heat breakdown.

Why does this matter in the kitchen?

Knowing which reaction you're relying on tells you how to control it.

For Maillard browning, focus on dryness and contact with heat. Pat food dry, preheat the pan, don't crowd it, and consider a pinch of baking soda to raise the pH for faster browning on onions or a glaze. A brush of milk or egg on pastry adds protein and lactose for a deeper crust.

For caramelisation, focus on temperature and timing. Use a heavy, light-coloured pan so you can see the colour, have your cream or butter ready before you start, and pull the pan off the heat a few seconds before it reaches the shade you want, because the sugar keeps cooking from stored heat. A squeeze of lemon or a pinch of cream of tartar helps by splitting some of the sucrose into glucose and fructose, which keeps crystals from forming.

Try it at home

This oven test lets you watch both reactions on one tray. Molten sugar is extremely hot, so don't touch it until it has fully cooled.

1. Preheat the oven to 175°C (350°F) and line a small tray with parchment paper.
2. Make two small piles, well apart: Pile A is 2 tablespoons of white sugar. Pile B is 2 tablespoons of white sugar mixed with 1 tablespoon of skim milk powder.
3. Bake, checking every 3 minutes, for up to 15 minutes.

What you'll see: pile B turns golden first and smells like biscuits, toffee and warm milk. Pile A stays white for longer, then melts at the edges into clear amber liquid with a sharper caramel smell. Once both have cooled, taste a crumb of each: B is rounder and more savoury-sweet, while A is pure caramel with a hint of bitterness.

Why: the milk powder supplies proteins and lactose, so pile B can brown through the Maillard reaction at a temperature where plain sugar is only just beginning to caramelise.

Chef Fizz says: Two piles of sugar, two completely different chemistries. Delicious science.

Common mistakes

• Calling every browned food caramelised. Seared steak and brown butter are Maillard browning. Knowing the difference helps you control it: dry surfaces for Maillard, careful temperature for caramel.
• Rushing caramelised onions on high heat. The outsides scorch before the inside softens and develops sugars. Cook them over medium-low heat for 30 to 45 minutes, adding a splash of water if they stick.
• Walking away from caramel. Sugar goes from amber to burnt in seconds once it passes 180°C (355°F). Stay at the pan and pull it off the heat just before it reaches your target colour.
• Expecting savoury flavour from sugar alone. Caramelisation can't make meaty or roasty notes, because sugar contains no nitrogen. For savoury depth, brown the protein properly.
• Using a dark pan for caramel. You can't judge colour against a black surface. A stainless or light-coloured pan lets you see exactly when to stop.
• Overdoing baking soda for faster browning. A pinch speeds the Maillard reaction, but too much tastes soapy and turns vegetables mushy. Stick to about 1/8 teaspoon per large onion.