Sugars. Heat. Pyrolysis. And what chefs and scientists know and don’t know about caramelization.
One of the pleasures of crème brûlée is the thin coat of slightly burnt sugar on top of the rich custard. This is often made by using a blowtorch on white table sugar (i.e. sucrose), and the sugar is transformed by the science of caramelization into a delicious golden brown slightly burnt layer.
Caramelization releases hundred of new compounds that give burnt sugar such a complex mix of flavors, aromas and colors. It takes place at high temperatures, beginning around 160°C/ 320°F.
During caramelization, sucrose is broken down by heat into its simple sugars fructose and glucose. Known as pyrolysis, it is a thermochemical decomposition of an organic compound. Volatile chemicals are released. Water molecules are lost as the sugars become dehydrated, and what is left of the sugar molecules combine to form a larger molecule.
These large molecules react further to form new compounds and polymers, and the color first changes to light yellow, and then to increasingly darker shades of brown (overdo this though, and it becomes black, thoroughly burnt, and unpleasant to taste).
That is why caramelization is also often also called browning. It is a form of non-enzymatic browning i.e. no enzymes are involved, just heat and temperature. It is in some ways, similar to the Maillard reaction, which is also often known as browning but there is a difference (more about that in another 1-Minute NomNom “Butter me up baby, I’ll be your sweet caramel”).
What we have described above are just a few of the more apparent chemical reactions that take place during caramelization. The thing is there are many more and scientists are still trying to understand all of them (Wikipedia says caramelization is poorly understood).
Not that that has stopped chefs and cooks. For a long time in the kitchen, they have been taking advantage of caramelization of the wonderful flavors and aromas that caramelization can give to food. Vegetables such as onions for example, are also often caramelized to give them an extra crunch and flavor.
The science may take a while to catch up, but as long as we have crème brûlée, that’s ok.
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