Rock candy is a simple sugar candy that can double as a science experiment. The process can take up to a week, but it’s fun to watch the sugar crystals growing over time. Note that the exact quantity of sugar syrup you will use depends on the size of the jar you have. If you want to make several pieces of rock candy, use multiple jars and skewers, and double or triple the sugar syrup solution as necessary. For easily printable instructions, please see the rock candy recipe.
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Assemble Your Ingredients
Prepare your materials: wash a glass jar thoroughly with hot water to clean it. To make rock candy on a wooden stick, cut a thin skewer until it is slightly taller than your jar. Use clothespins balanced across the top of the jar to clip it into place. This method is illustrated above. Alternately, you can make your rock candy on a string instead. Cut a length of thick cotton thread or kitchen twine a few inches longer than the height of the jar, and tape it to a pencil. Place the pencil across the lip of the jar, and wind it until the thread is hanging about 1 inch from the bottom of the jar. Attach a paper clip to the bottom of the thread to weigh it and ensure it hangs straight down.
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Add the Sugar One Cup at a Time
Begin adding the sugar, one cup at a time, stirring after each addition. You will notice that it takes longer for the sugar to dissolve after each addition.Continue to 5 of 10 below.
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Add Coloring and Flavoring
If you are using colors or flavorings, add them at this point. If you are using an extract, add 1 teaspoon of extract, but if you are using flavoring oils, only add ½ tsp, and make sure you don’t stand right in front of the pan—the scent can be very strong as it rises in the steam. Add 2 to 3 drops of food coloring and stir to ensure even smooth color.
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Insert the Skewer
Carefully lower the sugared skewer or string until it hangs about 1-inch from the bottom and fasten at the top with clothespins or balanced from a pencil. Do not let the end of the skewer or string come too close to the bottom or sides of the jar, or else the rock candy will grow into the sides of the jar.
Carefully place your jar in a cool place, away from harsh lights, where it can sit undisturbed. Cover the top loosely with plastic wrap or paper towel. You should start to see sugar crystals forming within 4-6 hours. If you have seen no change to your skewer or thread after 24 hours, try boiling the sugar syrup again and dissolve another cup of sugar into it, then pour it back into the jar and insert the string or skewer again.
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Grow Your Candy to Your Desired Size
Allow the rock candy to grow until it is the size you want. This process will take up to a week, depending on how large you want your rock candy. Don’t let it grow too large, otherwise, it might start growing into the sides of your jar! Once it has reached the size you want, remove it and allow it to dry for a few minutes, then enjoy or wrap in plastic wrap to save it for later.