In the simplest terms, caramelisation is the browning
process that occurs when sugar is heated.
However, there are numerous forms of
caramelisation depending on the types of sugars in the food and the kind of
reaction taking place.
The specific kind of browning taking place when you heat an
onion is called pyrolysis. This is a non-enzymatic form of browning, meaning it
isn’t taking place as a result of contact with oxygen, but rather a chemical
An easy way to picture the difference between non-enzymatic and
enzymatic browning is to imagine the contrasting reactions that a sliced apple
and sliced onion have to oxygen.
While a sliced apple will begin to turn brown
soon after making contact with the oxygen (aka. enzymatic browning), the sliced
onion will stay its same color even after prolonged exposure to air.
When Will The Caramelised Onion Take Place?
An onion can only be browned when it comes
into contact with a heat source, which causes a reaction that not only changes
the physical appearance of the onion, but also the chemical makeup. The key to
this reaction is the natural sugars that are already contained within raw
onions to transform them into delicious caramelised onions.
This chemical process occurs when the onion comes in contact
with heat, causing the temperature within the cells of the onion to rise.
this temperature reaches a certain point, pyrolysis occurs, causing the larger
starch and sugar molecules of the vegetable begin to break down into smaller
This happens when the heat causes the cellular bonds that link the large
sugars together to break apart, transforming them into the single molecules
that give the onion a sweeter, milder flavor.
Caramelising an onion to perfection requires time and
patience, as the onion — which is about 90 percent water to begin with — needs
to sweat out a significant amount of that liquid. This release of water is key
to the caramelisation process because this excess liquid allows the onion’s
structure to begin to break down, and for the vegetable to start to soften.
During this process the texture and appearance of the
vegetable is also altered, as the structural starches in the onion break down
as well, seemingly magically transforming the onion from yellow or white,
crunchy, and astringent to golden brown, soft, and subtly sweet.
You can then use the caramelised onions in many recipes, not just French onion soup; use them on pizzas, or serve just as a side dish, or use in pasta dishes to add a sumptuous flavor. They work perfectly well, too, in curries – see our ‘Off-piste’ recipes.
Excellent site with some old favourites together with some recipes which were new to me.