What Is Caramelization? Why Sugar Browns


Caramelization
Caramelization is non-enzymatic browning from the dehydration of sugars by heat.
The toasted part of a marshmallow has been carmelized. (John Lustig)
The toasted part of a marshmallow has been caramelized. (John Lustig)

Caramelization is one of the food browning processes, used to give foods a desirable color, flavor, and texture. It is also a process responsible for a burnt sugar flavor or blackening of food.

How Caramelization Works

Caramelization, like the Maillard reaction, is a form of non-enzymatic browning. It occurs when heating foods containing a high concentration of carbohydrates above a certain temperature. The temperature at which caramelization occurs depends on the type of sugar. The rate at which caramelization proceeds depends on the acidity or pH of the food. Caramelization occurs more quickly at neutral pH than under either acidic or alkaline conditions.

Note fructose has a lower caramelization point than other sugars. Baked goods containing fructose brown more readily than those made using other sugars and often end up darker in color.

Caramelization Temperature of Different Sugars

Here are the caramelization temperature of different types of sugars:

fructose: 110°C, 230°F
galactose: 160°C, 320°F
glucose: 160°C, 320°F
sucrose (table sugar): 160°C, 320°F
maltose: 180°C, 356°F

Caramelization is a process and not a single chemical reaction. As it occurs, water is removed from the carbohydrate. Isomerization and polymerization then take place. This is seen as melting, boiling, foaming, and darkening of sugar.

Caramelization is used to make candies, caramel, ghee, caramelized onions, and caramelized potatoes, among other foods. Foods that contain both carbohydrates and proteins brown from a combination of caramelization and the Maillard reaction.

How Caramelization Works in Sugar

Regular table sugar or sucrose is the best-studied carbohydrate for the carmelization process. It proceeds in the following manner:

  1. The disaccharide sucrose breaks down into the monosaccharides glucose and fructose. This is called a sucrose inversion.
  2. Condensation occurs, where the sugars lose water and react with each other, forming difructose-anhydride.
  3. Further dehydration occurs. Aldoses isomerize to ketoses.
  4. Molecules fragment and polymerize, producing the characteristic caramel color and browned sugar flavor associated with the process. The three main products from sucrose caramelization are the dehydration product caramelan (C12H18O9) and two polymers, caramelen (C36H50O25) and caramelin (C125H188O80).

Caramelization Flavors

Caramelization products have different flavors from each other. Here are some common compounds:

Diacetyl: Diacetyl forms during the first stages of caramelization. Diacetyl contributes a buttery or butterscotch flavor.
Hydroxymethylfurfural (HMF): Hydroxyacetylfuran (HAF) has a sweet aroma and flavor. Other furans have a nutty flavor.
Maltol: Maltol is the compound associated with the toasty flavor and aroma of freshly baked bread.
Esters and Lactones: These compounds have a sweet flavor, reminiscent of rum.

References

  • Miller, Dennis (1998). Food Chemistry: A Laboratory Manual. Wiley-Interscience. ISBN 978-0471175438.
  • Villamiel, M.; del Castillo, M. D.; Corzo, N. (2006). “4. Browning Reactions”. In Hui, Y. H.; Nip, W-.K.; et al. (eds.). Food Biochemistry and Food Processing. Wiley-Blackwell. pp. 83–85. ISBN 978-0-8138-0378-4.
  • Woo, K. S.; Kim, H. Y.; et al. (2015). “Characteristics of the Thermal Degradation of Glucose and Maltose Solutions”. Prev Nutr Food Sci. 20 (2): 102–9. doi:10.3746/pnf.2015.20.2.102