Making rock candy is quite simple when the proper steps are followed, and people have been making it within their homes since the ninth century. There are two basic methods that are used to produce the candy, called the precipitation and evaporation methods. In either case, making rock candy involves the growth of sugar-based crystalline formations. These formations, or candy as it will become, are a result of creating a supersaturated solution within a controlled environment that forces sugar molecules to be produced, and then grow outward from the mixture.
By combining a mixture that includes more sugar than what can dissolve in the amount of water that is being used, the sugar is able to separate from the solution and grow multiple molecules that protrude outward from the mixture. Called monoclinic crystals, the shape of the crystals that form from the solution are caused by the way the sugar molecules fit together. Food coloring is commonly used so that the finished candy is produced with a variety of appearances.
To make rock candy, water is poured into a bowl and heated until boiling, and then the proper amount of sugar is added. For example, a mixture of two cups of water and four cups of sugar would be an adequate amount in order to make rock candy. After the sugar has been added, and the mixture has been heated together, it is then poured into a separate container and allowed to cool. Flavorings such as lemon or lime juice can be added at this time to give the rock candy additional flavor, as well as any other type of artificial flavoring. What is produced by mixing these amounts of a solute and a solution is called a supersaturated solution.
A jar is probably the best container to pour the solution into, but be careful not to mess with the jar or touch its contents while the process is going on, which may take as long as seven days. Place sticks into the sugary syrup, these will later be used to hold the candy (being mindful to wet them first). When the sugar begins to grow out of the solution it will form upon the stick you place into the finished mixture, it is also a common practice to use a string upon which to grow the crystals.
Upon cooling, the growing process begins when the sugar starts to grow out of the solution by means of either of the two following methods. In the precipitation method of making rock candy, the sugar simply cannot dissolve and begins to release from the solution, forming crystals that reach upward. In the evaporation method it is the loss of water from the solution that causes the sugar to begin to grow molecules. Once a sufficient amount of water has evaporated from the jar, the sugar then begins the same process of separating from the solution as it does in the precipitation method.
Molecule by molecule the sugar grows, and forms the familiar crystalline forms. Once the process has begun, the crystals fit together in various forms. The serving size is controlled by the placement of the stick or string into the mixture, this also ensures that the crystals are produced on a handle that allows the user to hold the candy while they are consuming it.