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Carmelization Chemistry – Why Sugar Browns

The toasted part of a marshmallow has been carmelized. (John Lustig)

The toasted part of a marshmallow has been carmelized. (John Lustig)

Carmelization 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 Carmelization Works

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

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

Carmelization Temperature of Different Sugars
Sugar Temperature
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

Carmelization 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.

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

How Carmelization 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 carmelization are the dehydration product caramelan (C12H18O9) and two polymers, carmelen (C36H50O25) and caramelin (C125H188O80).

Carmelization Flavors

Carmelization 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.

Bake a Chocolate Volcano Souffle to Model a Real Volcano

Pu'u 'O'o, a Hawaiian volcanic cone (G.E. Ulrich - pubs.usgs)

Pu’u ‘O’o, a Hawaiian volcanic cone (G.E. Ulrich – pubs.usgs)

You know you can make a baking soda and vinegar volcano to simulate a volcanic eruption or you can use other ingredients like yeast and peroxide or citric acid and baking soda, but have you considered how the cooking of a souffle is a volcano simulation?

While the bubbles formed by the chemical reactions used to make ‘volcanoes’ behave somewhat like magma and gases, a souffle probably is a better simulant because the egg whites of a souffle harden sort of like lava hardens into rock. Lava can be foamy as the gases in magma come out of solution, forming bubbles of steam, carbon dioxide, and other gases. When a souffle is cooked, the air bubbles and steam trapped by the egg expand, causing the souffle to rise. When the gas bubbles form in magma expand, they can forcefully bubble the magma up so that it erupts as lava. If a souffle overflows its dish, you get a foamy mess that rolls down the side of the pan and eventually hardens as the egg cooks. When lava erupts from a volcano, it can cascade down the side of the cone, with the lava hardening into rock.

Are you ready to try out an edible chemical volcano? Here’s a chocolate volcano souffle recipe. It’s a little more complicated than mixing baking soda and vinegar, but it tastes a whole lot better, so it’s worth the trouble.

Individual Chocolate Souffles

  • 1/3 cup granulated sugar
  • 5 ounces bittersweet chocolate, chopped or grated
  • 3 egg yolks, room temperature
  • 6 egg whites, room temperature
  • pinch of salt
  • butter or nonstick cooking spray
  • granulated or powdered sugar or cocoa powder
    1. Preheat the oven to 375°F.
    2. Butter or spray 6 personal-size ramekins. Sprinkle the inside of the ramekins with granulated sugar.
    3. Melt the chocolate in a bowl that you have set inside of a pan of very hot water.
    4. Once the chocolate is melted, remove the bowl from heat and whisk in the egg yolks.
    5. In a separate bowl (preferably copper), beat together the egg whites plus a pinch of salt until soft peaks form.
    6. Gradually add the 1/3 cup sugar. Continue beating the egg whites until they hold stiff peaks.
    7. Stir a spoonful of the egg whites into the chocolate mixture to lighten it, then fold in the remaining egg whites. Continue folding until the mixture is uniformly-colored.
    8. Equally divide the mixture between the 6 prepared ramekins.
    9. You can bake the souffles right away or can allow them to rest for up to 30 minutes. Bake for 12-15 minutes, until the souffle is set and the tops are crusty.
    10. Sprinkle the souffles with your choice of powdered sugar, granulated sugar, or cocoa powder.
    11. Enjoy your treat and try to imagine the tasty chocolate confection is molten lava, which is what it will feel like on your tongue if you don’t let the ramekins cool enough before diving in.