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Rock candy is a delicious and easy science experiment that you can try right in your own kitchen. You can wrap the candy around skewers or strings and add any colors or flavors you like!
Ingredients
- 2 cups of water
- 4 cups of white sugar
- Food coloring (optional)
- Flavoring (optional)
Steps
Prepare the Sugar Water Solution
Boil 2 cups of water. Ask for adult assistance if you're not allowed to use the stove, as boiling water can be dangerous if spilled.
- Use purified water if possible. Tap water may contain impurities that could cause the sugar to stick to particles, making it difficult for the candy to form around the string.
- If you don't have a stove, you can use a microwave. Stir the sugar into the water in a microwave-safe bowl, and heat on high for about 2 minutes. Afterward, stir until the sugar dissolves, then heat for another 2 minutes. Stir the mixture again, and by this time, the sugar should be fully dissolved.
- Be sure to use oven mitts or pot holders to avoid burns when removing the pot from the stove or the bowl from the microwave.
Stir 4 cups of sugar into the water, adding ½ cup at a time. Stir the mixture each time you add sugar until it dissolves. Once the solution becomes saturated, the sugar will take longer to dissolve. It may take around 2 minutes for the sugar to fully dissolve in the water.
- Continue stirring until the solution becomes clear. If the solution appears cloudy or the sugar stops dissolving, turn up the heat to bring the water to a rolling boil. Hotter water can dissolve more sugar, so increasing the heat will help dissolve the remaining sugar.
Remove the sugar water solution from the heat and let it cool for about 15-20 minutes. It's important that there are no undissolved sugar crystals left at the bottom of the pot. If there are, the candy won't stick to the string but instead to the undissolved sugar.
- If the sugar doesn't fully dissolve while stirring in hot water, strain the solution through a fine sieve and keep only the liquid.
- The solution you have now is saturated, meaning it holds more sugar than it can at room temperature. As the solution cools, its saturation point lowers, and it can no longer hold the excess sugar. The dissolved sugar will solidify and adhere to the string or skewer.
Add color or flavor if you want to make your rock candy more interesting. Try matching the flavor with the color — blue could have a blueberry flavor, red could be strawberry, and purple could be grape for easy flavor identification. Be sure to stir the flavor and color evenly into the mixture.
- Just a few drops of flavoring are enough, but it's best to make the color bold for the best results.
- You can use drink powders like Kool-Aid to add both flavor and color to your candy.
- Try adding fruit juices like lemon, orange, or other candy flavors.
- Experiment with extracts such as mint, strawberry, vanilla, or banana.
Pour the syrup into a glass cup or jar that you will use to make the candy. The container should be tall and cylindrical, made of glass, as plastic will melt when hot syrup is poured into it. Fill the container nearly to the top.
- Ensure the cup is clean and free from any dust particles. Sugar can adhere to dust, but you only want the sugar to form and stick to the string or skewer.
- Cover the cup with parchment paper to prevent dust from settling on the sugar syrup surface.
Making Crystallized Candy with String
Tie one end of the string to the center of a pencil and the other end to a paperclip. The paperclip will act as a weight, pulling the string down to keep it from touching the sides of the cup. The string should be about two-thirds of the height of the cup; don’t make the string too long, or the paperclip may touch the bottom of the cup. With this length, the candy will form more easily. If the string touches the bottom or comes too close to the sides of the cup, the candy will be small or misshapen.
- Use a natural fiber string like braided or cotton thread. Fishing line or nylon thread is too smooth for the sugar to stick and crystallize properly.
- You can also use a small metal piece or pin to tie the string or even a bit of crystallized candy to help the formation process speed up.
- The pencil should be long enough to rest comfortably on the edge of the cup without falling in. You can also use a knife, skewer, or popsicle stick. A knife or popsicle stick might be more stable as they sit across the top of the cup without rolling.
Dip the string into the syrup solution, then pull it out and place it on parchment paper to dry. Keep the string taut as it will harden as the syrup cools. As the water evaporates, you'll notice sugar crystals starting to form on the string, which serve as the initial crystallization that speeds up the candy-making process.
- Make sure the string is completely dry before proceeding to the next step, and be careful not to let any of the initial crystals fall off when dipping the string back into the syrup.
- You can skip this step or speed up the process by wetting the string and rolling it in granulated sugar (just ensure the string is completely dry before dipping it back into the syrup and that no sugar falls off), which will create initial crystals and increase the chances of a successful candy formation.
Place the string into the syrup solution with the pencil resting across the top of the cup. The string will hang straight down, not touching the bottom or sides of the cup. Cover the cup with a paper towel. Avoid sealing the top with materials like plastic wrap, as evaporation is a key part of this process.
- As the water evaporates, the remaining syrup will absorb more sugar, and the water pushes the sugar out. Sugar molecules will stick to the string and begin to form the crystallized candy.
- Use tape to secure the pencil in place to prevent it from rolling or shifting during the candy-making process.
Place the cup in a secure, undisturbed location. For larger crystal candy, choose a cool, shaded area as slower evaporation gives the candy more time to form.
- If you want to speed up the crystallization process and don't mind smaller candy, place the cup in a sunny spot to accelerate evaporation.
- Movement or shaking can affect the candy's formation. Set the cup on the floor in a quiet area, away from music, radio, or TV noise.
Wait for a week to allow the candy to form. Avoid touching or tapping the cup, as this can disrupt the crystallization and cause some candy to fall off. After a week, you will see a large cluster of crystal candy surrounding the string.
Carefully remove the string from the sugar solution and place it on parchment paper to dry. Use scissors to cut off the paperclip from the string.
- If the candy sticks to the cup, pour hot water around the outside of the bottom of the cup. This will reduce the stickiness of the sugar, making it easier to pull the string out without damaging the candy.
Making Crystallized Candy with a Skewer
Wet the skewer or popsicle stick with water and roll it in granulated sugar. The sugar crystals will serve as a starting point for crystallization, allowing the dissolved sugar to adhere and form crystallized candy. The crystallization process makes it easier for the candy to form and shortens the time required since the sugar has a surface to latch onto.
- Make sure the skewer is completely dry before moving on to the next step. If the sugar doesn't adhere properly, it will fall into the cup, causing the sugar to crystallize at the bottom rather than on the skewer.
Position the skewer in the center of the cup to avoid it touching the sides or bottom. If the skewer touches the cup, it will interfere with the candy formation or cause the candy to stick to the bottom and sides of the cup.
- Keep the skewer approximately 2.5 cm from the bottom of the cup.
Clamp the other end of the skewer with a clothespin and place the pin horizontally across the top of the cup. The skewer should be secured in the middle of the clothespin, as close to the spring as possible. If the cup has a wide opening, you may use a larger clothespin.
- Ensure the skewer is firmly held in place by the clip and remains centered in the cup.
- Cover the cup with a paper towel. You can tear a small hole in the towel to allow the skewer to pass through.
Place the cup in a safe, undisturbed area. Music, TV sounds, or other activities can cause vibrations that may interfere with the crystallization of the candy or cause it to fall off the skewer. To ensure the best candy formation, keep the cup in a cool or room-temperature area, away from noise and foot traffic.
Wait 1 to 2 weeks for the candy to form. Avoid touching or tapping the cup as this could cause the candy to fall off the skewer. Once you are satisfied with the amount of candy (or when it seems like the candy can't form any larger), carefully remove the skewer and place it on parchment paper to dry.
- If there is a hardened layer on the surface of the sugar solution, you can gently use a knife to break it off, but avoid disturbing the area near the candy skewer.
- If the candy sticks to the cup, pour hot water around the outside of the cup’s bottom. This will reduce the stickiness of the sugar, allowing you to remove the skewer without damaging the candy.
You're done!
Tips
- This recipe is perfect for a science fair project or conducting scientific experiments.
- If no candy has formed on the string after a day, remove the pencil and string and reheat the sugar solution, adding more sugar and stirring. If you need to add more sugar, it means you didn't add enough in the initial step. Now, you can proceed with making candy using the supersaturated sugar solution.
- Be careful not to add too little or too much sugar, as the candy will not form properly.
- This recipe may take longer than expected, so patience is key.
- When making the sugar syrup in the microwave, watch it closely to prevent it from overflowing.
- Make sure the handle of the pot is positioned in a way that prevents accidental contact, to avoid spilling hot syrup.
Warnings
- Do not stir or insert your hand into the jar/cup. This will interfere with the formation of the crystal structure of the candy. While it won't ruin the process, it will make it more difficult for the candy to form properly.
What You’ll Need
Make the Sugar Syrup Solution
- Pot or pan
- Wooden spoon
Make Crystal Candy with String
- Popsicle stick, wooden skewer, knife, or pencil
- String
- Paperclip or round metal piece
- Tall, deep cup or jar (avoid plastic materials)
Make Crystal Candy with Skewer
- Popsicle stick or wooden skewer
- Clothespin
- Tall, deep cup or jar (avoid plastic materials)
