Fondant and rock sugar are both crystalline candies. And they are a great way for anyone to understand and observe the principles of crystallization. Seriously, this is a great teaching lesson for school children and any interested adult. If you’ve read my post about the theory of candy crystallization, then consider this the practical course.
Fondant gets crystallized quickly at a temperature when the rate of crystal nucleation is maximal. Rock sugar, on the other hand, gets crystallized slowly at room temperature. And in both cases, we end up with a delicious product to eat.
You might know fondant as that fancy cake decoration. It is a kind of sugar dough that can be shaped like playdough. But fondant can not only be used as a cake frosting, it can also be used in candy bars or pralines as a filling or coating.
The important thing is that you start the crystallization at the right temperature. At home, that is 50 °C (120 °C). That is when you start to knead the candy mass until it resembles a smooth dough. I’ve drawn the production process for fondant in the phase diagram below.
Before I get to the recipe, I have a few questions that you should be able to answer if you’ve read my post about crystallization.
1. Why do we induce the crystallization of fondant at 50 °C (120 °F) and not immediately after the syrup is taken off the stove?
2. What does the structure of fondant look like? What are the two co-existing phases?
3. Why is fondant opaque and not clear like rock candy?
Could you answer all the questions? Here are the answers:
1. The nucleation rate and overall crystallization rate is highest in the “center” of the rubbery zone. If we induce crystallization the second after we take the syrup off the stove, the crystal growth will be favored over the nucleation in the first phase of crystallization. This is because of the low level of supersaturation at higher temperatures. This gives us a fondant with a gritty texture and large crystals in it.
2. Fondant is a saturated sugar solution with small dispersed sucrose crystals. The two co-existing phases are saturated syrup (a viscous liquid, the continuous phase) and tiny sucrose crystals (the dispersed phase).
3. Fondant is opaque because it gets aerated while kneading.
Did you get all the answers right? Congratulations! If not, you can always go back and check out posts #1-3 of my candy-making series. Let’s get to the recipe.
- 500 g granulated sugar
- 25 g glucose powder
- 1/2 cup water
- powdered sugar, for dusting
- flavoring extract of your choice, to taste
- food coloring of your choice
- In a pot with high sides, combine the sugar, glucose, and water. Cook the syrup, without stirring, to 114 °C (238 °F). Pour the syrup into a baking pan. Don’t scrape down the sides or bottom of your pot. You don’t want to introduce any seed crystals at this stage. Let the syrup cool down undisturbed until it reaches 50 °C (120 °F).
- Stir the syrup with a wooden spoon. You will see that the syrup will become opaque (because of the aeration). Continue to stir the fondant until it becomes so thick and stiff that it is difficult to stir and starts to crumble. Dust your work surface with powdered sugar and wet your hands. Grab the fondant and knead it on your work surface as if needing a bread dough until the texture is smooth. If the dough becomes sticky, dust it with more powdered sugar. After kneading, the dough shouldn’t be crumbly anymore. It should be supple and pliable.
- If you like to give the fondant a special color or flavor, you can now briefly knead in the flavor extract or food coloring of your choice. Wrap the finished fondant in plastic wrap and leave it to sit overnight before using. Fondant can be stored at room temperature for up to one month.
In Rock candy, we want the opposite of what we want in fondant. We want the sugar to grow into a beautiful large crystal. I’m not a big fan of licking on rock candy but in tea it is magic. I love to observe how rock candy slowly dissolves in my cup of tea.
As for the fondant, I have a few questions for you that can help you to check your level of comprehension:
1. Why does the crystallization process take so much longer for rock candy (up to two weeks at room temperature) than for fondant (up to 1 day at 50 °C (120 °F))?
2. When producing rock candy, you dip wooden skewers that are coated with granulated sugar in a supersaturated syrup. Why do we coat the wooden skewers with granulated sugar?
3. When will the growth of a rock sugar crystal out of a supersaturated sugar solution come to a stop? Assume that the sugar solution doesn’t get changed or renewed during crystallization.
And here are the answers:
1. The lower the temperature, the slower the crystallization speed.
2. The granulated sugar crystals are used as seed crystals to induce crystallization.
3. The sugar crystal can only grow as long as the syrup used for dipping is supersaturated. All the sugar molecules that can be dissolved in the water will stay dissolved. This limits the maximum size of your rock candy. To make the crystal grow further, you would need to replace the saturated dipping solution with an oversaturated syrup.
For coating the skewers:
- 50 grams granulated sugar
For the syrup:
- 600 grams granulated sugar
- 1 cup water
- a few drops of liquid food coloring
- Lightly wet the bottom half of the wooden skewers and roll them in granulated sugar to tightly coat them. These are the seed crystals for the rock candy.
- In a pot with high edges, combine half the sugar and all the water for the syrup. Heat the syrup until all the sugar is dissolved. Then add in the rest of the sugar and boil the syrup again until all the sugar is fully dissolved. Leave the syrup to cool for 20 minutes. Then stir in a few drops of the food coloring.
- Divide the syrup evenly among 6 mason jars. Place a wooden skewer in each jar but make sure it doesn’t touch the bottom of the jar. It should just be dipped in the syrup. You can secure the skewer with clothespins.
- Leave the skewers in the mason jars and wait for the sugar to crystallize at room temperature. The longer you wait, the larger your rock candy will be. You can wait anywhere from 3 days to 2 weeks. Remove the sticks from the mason jar once you are happy with the size of your sugar crystal.