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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.

Peep S’mores Easter Science Project

When you microwave Peep s'mores (or any marshmallow) the water vapor inside the candy expands, forming a hot foam. (Qfamily)

When you microwave Peep s’mores (or any marshmallow) the water vapor inside the candy expands, forming a hot foam. (Qfamily)

Happy Easter! Here’s a simple recipe for Peeps™ s’mores and a look at the science of why Peeps get so crazy big in the microwave.

Peep S’mores Ingredients

  • graham crackers
  • Peep candies
  • chocolate kisses (or chocolate bar pieces)

The recipe is easy and fun. Take a graham cracker, set a Peep on it, put a couple of Hershey’s Kisses™ on another cracker, pop them in the microwave, and nuke them until the Peep has expanded so it looks like it’s ready to explode (20 seconds seems good). Smush the Peep side and the Kiss side together, and enjoy!

Peep S’mores Science

Peeps are marshmallows, which are puffed table sugar. Table sugar is purified sucrose. Sucrose, like other sugars, is composed of hydrogen, carbon, and oxygen atoms bonded together. When you microwave Peep s’mores, the energy added to the candy causes the molecules to vibrate. The bonds holding sucrose together loosen, softening the marshmallow, while the water vapor inside the candy expands, exerting pressure on the sugar. Expanding water forms bubbles that cause the Peep to get larger and larger. If you leave the microwave on too long, eventually you’ll supply enough energy to start combustion of sugar. This reaction between oxygen and sucrose leaves you with a burnt marshmallow, and possibly a small fire in your appliance.

Here’s a bit more about sugar for you, to read for the 20 seconds it will take you to nuke a s’more and unwrap Kisses for another one:

Make Fake Glass – If you heat sugar, you can make hard candy out of it. If you spread the hard candy onto a cookie sheet, you can make stage ‘glass’.

Grow Sugar Crystals – Rock candy is made from sugar crystals. These crystals are fairly easy to grow, plus you can eat the finished product.

Experiments on Peeps – Neat website that discusses experiments on Peeps.

Instant Fire Demonstration

Instant Fire Chemical Reaction (deradrian)

Instant Fire Chemical Reaction (deradrian)

Make instant fire using sugar, potassium chlorate, and sulfuric acid. No matches or flame is needed for this exciting chemistry demonstration!

Instant Fire Materials

You only need three chemicals for this reaction:

  • potassium chlorate
  • granulated table sugar – sucrose
  • sulfuric acid

Perform the Instant Fire Demonstration

You can do this demonstration in a test tube or on a heat-safe dish. Goggles, gloves, and a lab coat are recommended. Don’t use glassware you value too highly, since there is a good chance the highly exothermic reaction will shatter it.

  1. Mix together roughly equal amounts of potassium chlorate and sugar.
  2. Add a drop or two of sulfuric acid to the mixture to start the reaction. That’s it! Expect purple flames, smoke, and heat.

How It Works

The chemical reaction for this demonstration is:

2KClO3(s) + heat —> 2KCl(s) + 3O2(g)

This is a decomposition reaction in which potassium chlorate breaks down in potassium chloride and oxygen. Potassium chlorate is a powerful oxidizer. Adding sulfuric acid provides enough heat to accelerate the reaction. Once there is sufficient heat, the oxygen from the reaction burns, using sugar as the fuel.

Dancing Gummy Bear Variation

Another way to do this demonstration is to make a candy, such as a gummy bear, appear to dance in the flames.

  1. Secure a large test tube to a ring stand to hold it in place and so you’ll be able to distance yourself from it.
  2. Heat a small amount of potassium chlorate in a large test tube.
  3. Once the potassium chlorate has melted, add a gummy bear candy.

See the Instant Fire Reaction in Action

Here’s a quick video of this chemical reaction, so you can see what to expect. There are two things you’ll notice here. First, the potassium compound produces a bright purple flame, just as you would expect from a potassium flame test or bead test. Second, it’s important to use a heat-safe container and surface and proper safety gear when performing this reaction, because once it takes off, it gets exciting quickly!


More Fire Science

How To Make Rock Candy or Sugar Crystals

Rock Candy or Sugar Crystals

Sugar crystals are one of the few types of crystals you can grow that you can eat. (Anne Helmenstine)

Sugar crystals are called rock candy because these hard crystals are edible. Sugar (sucrose) crystals are one of the few types of crystals you can grow and eat. You can eat the natural clear crystals or you can color and flavor them.

Rock Candy Materials

  • 3 cups sugar (sucrose)
  • 1 cup boiling water
  • food coloring (optional)
  • flavoring (optional — good choices include cherry, peppermint, and cinnamon)
  • clean glass or plastic jar
  • wooden skewer or cotton string

Grow Sugar Crystals

The procedure is really easy.

  1. Dissolve the sugar in the boiling water. You can heat the sugar solution on the stove or in the microwave if you have trouble getting the sugar to dissolve.
  2. Add a few drops of food coloring and flavor, if desired.
  3. Allow the solution to cool a bit before pouring it into your jar. You don’t want to get burned!
  4. Pour the sugar solution into a jar. Place a wooden skewer into the jar or else hang a string into the middle of the jar, tied to a pencil or butter knife.
  5. Place the container somewhere it won’t be disturbed. You may wish to cover the jar with a paper towel or coffee filter to allow evaporation while keeping the crystal solution clean.
  6. It may take a few days to get good crystal growth. If you see crystals forming on the top of the jar, you can remove them and eat them. If you leave them, these crystals will compete with your stick or string for sugar and will reduce the size of your crystals.
  7. Remove the crystals and enjoy them! If you want to store the crystals before eating them, keep them in an airtight container so humidity in the air won’t make the rock candy sticky.

Easy Rainbow Density Science Project

Rainbow Density Column

The rainbow effect in this colored sugar column persists for months. (Anne Helmenstine)

Traditional density columns layer immiscible liquids (ones that won’t mix), such as oil and water. One advantage of this type of density column is that you can shake the container and the liquids will separate. One disadvantage to using immiscible liquids is that you quickly run out of either readily available or non-toxic chemicals to layer. However, you can make a completely non-toxic density column, using as many layers as you want, by changing the concentration of a safe soluble chemical in water. For example, this project makes a rainbow density column using colored sugar and water. It’s really easy to do, can be made in any combination of colors, and lasts virtually forever. (I say virtually because eventually you’ll get crystals in the column, but it’s good for a couple of months at least).

Rainbow Density Column Materials

  • sugar (ordinary table sugar, which is sucrose, though you can other other sugars)
  • hot water
  • food coloring
  • tall, thin column (vase, graduated cylinder, small glass, etc.)
  • enough cups or bowls for all the colors you want

Procedure

  1. First, plan your colors. You will make a separate sugar solution for each layer. A rainbow is nice because it doesn’t matter if the colors bleed into each other a little where the layers meet.
  2. Make the solutions. The bottom layer has the most sugar, with less sugar in each of the layers above it. The top layer can be pure water, if you like. I made the bottom solution with 5 tablespoons of sugar and 3 tablespoons of water; next layer was 4 tablespoons sugar and 3 tablespoons of water; next layer was 3 tablespoons of sugar and 3 tablespoons of water; next layer was 2 tablespoons of sugar and 3 tablespoons of water; top layer was 1 tablespoon of sugar and 3 tablespoons of water. You may need to heat the solutions to get the sugar to dissolve. I have best luck using boiling water, at least for the most concentrated solutions, but if you have young helpers, you might want to stick with hot tap water. The amounts of sugar and water are not critical, so long as the lowest layer has the most sugar and each layer above it has less sugar.
  3. Add a drop or two of food coloring to each container. I used purple, blue, green, yellow, red. If you look at the picture, you can see the most blending between colors occurs at the top of the container, where the solutions aren’t as concentrated. Do not go crazy with the food coloring or you won’t be able to see through the liquids and you’ll miss the colors!
  4. If you used boiling water, let the solutions cool a bit before layering them. You don’t want to get burned.
  5. Now layer the liquids. Start with the solution with the most sugar. Pour it into your container. You may not need to add all of the liquid, depending on the size of your display container.
  6. Layer the next solution on top of it. You want to disturb the lower layer as little as possible, so you can slowly pour the liquid down the side of your container, pour the liquid over the back of a spoon, or use a straw to pick up liquid and dispense it on top of the next layer.
  7. Continue adding layers until you reach the top.

You can use the rainbow density project as a decoration or to teach principles of density, concentration, and color theory. I have not had trouble with the column attracting ants, but it will draw dust, so you may wish to cover it. Avoid disturbing it, to prevent the colors from mixing. When you clean out the container, use hot water to dissolve any sugar that may get stuck inside.

Tip: If you want to drink the density column, you can, but it will taste a lot better if you use powdered drink mixes. You can use sweetened powdered drink mix (if it contains sugar) instead of the sugar and food coloring. If you have unsweetened drink mix, use it in place of the food coloring.