What is the Science Behind Sugar Caramelization?
- Ester Lilaj
- Dec 15, 2025
- 2 min read
Caramel itself doesn’t look like a very complex substance; when you watch sugar caramelize it seems to melt and somehow transform to become an amber syrup with new flavors and tastes. Often oversimplified, the process of caramelization actually involves multiple chemical reactions that work to break down and rearrange sugar to form hundreds of new compounds, which then produce the distinct flavors, color, and smell of caramel. So, let’s break down caramelization and take a look at the chemical reactions that make it work.
In this breakdown, we’ll focus on sucrose (table sugar) as the sugar to caramelize, though many other sugars caramelize as well. Firstly, as you heat sucrose, it begins to soften into a thick clear liquid. As the temperature rises, the sucrose molecules move around faster and bump into each other more frequently. At around 160°C (though caramelization happens at different temperatures for different sugars),sucrose absorbs enough heat energy to weaken and break the glycosidic bond that holds fructose and glucose together. This means that the sugar begins to break apart from sucrose to glucose and fructose, its monosaccharides. Glucose and fructose are more reactive than sucrose and are able to move around easily, allowing them to caramelize.
After sugar is hydrolyzed, dehydration occurs where hydrogen and oxygen atoms of the sugar molecules break off and combine to chemically form water that is then released. Losing this water makes the glucose and fructose more reactive and unstable which sets the stage for the sugars to rearrange into ring structures, aldehydes, and ketones. The changes here are observable; the clear thick liquid that was seen before is now even thicker and begins to take on a golden color.
Next the process of fragmentation occurs because these new carbonyl-containing structures are highly reactive and therefore prone to breaking apart into even smaller compounds. Fragmentation creates important compounds like diacetyl (classic caramel scent), acetoin (smooth caramel), acetic acid and formic acid (sweetness balance), and furan compounds (nutty taste).
The final step of caramelization, polymerization, gives caramel its full amber color as well as thickens its texture. During polymerization, all the highly reactive compounds formed during dehydration and fragmentation begin to react with one another and form larger compounds. At this point, the temperature has reached somewhere around 180°C to 200°C. This high heat helps the highly reactive compounds form bonds with one another and form three main caramel pigments: caramelan, caramelen, and caramelin.
Caramelan is the smallest of the three and has characteristics of a sweeter and milder taste as well as a light amber color. Caramelen increases in size and complexity and has a deep amber color with a rich flavor, typically the ideal caramel. Lastly, caramelin is the biggest of the three and has a darker color and a more bitter taste, only increasing in quantity as the temperature continues to rise.
Ester Lilaj is a rising junior at McLean High School in McLean, Virginia. She volunteers at various food banks in her area, helping organize inventory and serving members of the community. She is interested in food safety and preservation.
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