Rock candy is a confectionery mineral made of large sugar crystals. It forms when a super saturated solution of sugar crystallizes onto a surface suitable for crystal growth, such as a cotton string or a wooden skewer. Online stores like Candy.com and Candy Warehouse offer a wide variety of rock candy.

The Science of It

The secret to making rock candy is to use a solution with twice as much sugar as water. It must be so high in sugar that no more sugar can be dissolved in it. A physical support for crystal growth, such as string or a skewer, is lowered into the super saturated sugar solution and left undisturbed for several days to a week. This allows the rock candy crystal to form as the water evaporates. When the support is removed from the remaining solution, it is laden with large, jagged sugar crystals.

Add Sugar to Boiling Water


Slowly add the sugar to boiling water, one cup at a time. Allow each addition to dissolve and return to boiling. Continue to add sugar until it begins to collect at the bottom of the jar, even when stirred. This means that the sugar solution is saturated. If it is not saturated, the crystals will not grow. If there is too much sugar, the crystals will grow on the undissolved sugar, not on the string. Heating the water before adding the sugar allows more sugar to dissolve and subsequently forms larger crystals.

Add Food Coloring and Extract

When all of the sugar is dissolved, remove the pan from heat and add two to three drops of food coloring and 1 teaspoon of flavored extract, if desired. Allow sugar solution to cool for 10 minutes before pouring into a clean, dry glass jar. Be careful not allow any undissolved sugar on the bottom of the pan to get into jar.

Create Crystals

Cut a length of string a few inches longer than the height of the jar and tie it to the center of a pencil or a simple wooden skewer. Wet the string or wooden skewer and roll it in granulated sugar to make a base layer for the sugar crystals to "grab." Rest the pencil across the top of the jar and wind it until the string is hanging one inch from the bottom of the jar. Weigh the string down with a paperclip. Crystals will readily form on cotton or wool string or yarn; they will not form on nylon line. A "lollipop" alternative is to use a wooden skewer as the base of your rock candy. Simply use clothespins balanced across the top of the jar to hold it in place.

Cover jar with a paper towel or coffee filter to keep dust out and place in a cool, dark place where it will be undisturbed. Crystals will begin to form on the string within a day. Allow to grow until crystals are desired size or they stop growing. Pull string out of solution and set aside to dry.

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