Daily Junction.mobi portalFood · October 29, 2023 · Amelia Hart · 6 min
Caramelisation is what happens when sugar is heated until it browns, sweetens and turns nutty. Here is the science behind it, how it differs from the Maillard reaction, and how to get it right at home.
Tip a spoonful of sugar into a dry pan, leave it over a steady flame and watch. First it sits there, white and inert. Then it melts to a clear syrup, takes on a straw colour, deepens to amber, and fills the kitchen with a smell somewhere between toffee, toast and treacle. Nothing was added — no butter, no cream, no flavouring. That transformation, from plain sweetness to something complex and golden, is caramelisation, and it is one of the most useful pieces of chemistry a cook can understand.
Caramelisation is the browning of sugar that happens when it is heated to a high enough temperature, breaking the sugar down into hundreds of new aroma and colour compounds. It is a form of pyrolysis — heat-driven decomposition — but applied specifically to sugars rather than to proteins or fats.
When you heat ordinary table sugar, the heat first melts it, then begins to tear the sugar molecules apart. Those fragments react with one another and recombine into a huge family of new substances: some are dark and bitter, some are intensely sweet, and many are volatile, which is why caramel smells so strongly. The result is the familiar golden-to-brown colour, the nutty, slightly bitter depth, and the rounded sweetness that no raw sugar can offer.
Crucially, caramelisation needs only sugar and heat. There is no water, protein or fat required for the core reaction, although in practice we often add butter or cream afterwards to make sauces and sweets.
Sugars are not all the same, and they do not all caramelise at the same point. As a rough guide:
This is why a drizzle of honey, which is rich in fructose, browns so eagerly under the grill, and why fruit edges catch and char before the rest of a tray of roast vegetables. It also explains why recipes are fussy about temperature: the difference between a pale, mild caramel and an acrid, burnt one can be only a few degrees and a few seconds.
As the sugar darkens, two things happen at once. Flavour deepens — from simple sweetness to butterscotch, then toffee, then a pleasant bitterness — and sweetness actually falls, because the sugar molecules driving sweetness are being broken apart. A very dark caramel can taste almost savoury, which is exactly why chefs use it to balance puddings and sauces.
People often use "caramelising" loosely to mean "browning," but there are really two browning reactions in the kitchen, and they are not the same thing.
The seared crust on a steak, the golden top of a loaf, the colour of roast coffee and the skin on roast chicken are mostly Maillard, because those foods are rich in protein. A pan of melting sugar is pure caramelisation. In many foods the two overlap: the brown edge of a roast onion, for instance, comes partly from the onion's natural sugars caramelising and partly from Maillard browning. If you want to go deeper on heat-driven flavour, our guide to pasteurisation shows how temperature changes food in a very different way, by killing microbes rather than building flavour.
Once you know what caramelisation is, you start to notice it everywhere:
It also lends colour and a faint bitterness to some drinks and sauces, and "caramel" colouring is used industrially in everything from cola to gravy browning.
Caramelisation rewards patience far more than firepower. A few practical rules:
One warning worth repeating: molten caramel is extremely hot, far hotter than boiling water, and sticks to skin. Keep children away, never taste it straight from the pan, and have a bowl of cold water nearby.
Caramelisation is one of the simplest ways to add depth without adding ingredients. Browning the onions properly before a stew, roasting vegetables until their edges colour, or letting a sauce reduce to a deeper shade all build flavour from sugars that were there all along. It is the same instinct behind getting a good crust on baked goods, where heat and sugar combine — closely related to the changes that happen during proving and baking dough. And because caramel is also the base of so many sauces, understanding how it behaves alongside fats helps when you move on to richer techniques such as emulsification.
Caramelisation is the browning of sugar under heat — a controlled bit of chemistry that turns plain sweetness into deep, nutty, golden complexity. Keep it separate in your mind from the Maillard reaction, which also needs protein, and remember that the whole process hinges on temperature and timing. Use a heavy pan, moderate heat and your senses, take it off a moment early, and you will turn the cheapest ingredient in the cupboard into one of the most flavourful.
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