How to make rock candy

How to make rock candy

Rock candy has been around for centuries. Made simply from sugar and water, this crystallized sugar delight is loved by adults and kids of all ages. While making rock candy is a relatively simple procedure, it is also considered an art form.

Not only are you attempting to grow crystal sugar candy, but you are also attempting to grow crystal sugar candy with the largest crystals possible. Adult supervision should be employed as boiling water is very dangerous and can cause serious burns.

Items you will need:

  • Measuring cup
  • Heavy metal pan
  • Long Wooden spoon
  • Glass jar (canning jar or olive jar work well)
  • Clean cotton string or cotton twine (nylon thread or fishing twine will not work)
  • Pencil
  • Paper clip or galvanized washer (do not use a leaded fishing weight as lead is poisonous)
  • Candy thermometer


1 cup water
Approximately 2 cups of granulated sugar
Flavoring agent such as vanilla or peppermint extract (optional)
Food coloring (optional)

Begin with an extremely clean glass jar. A canning jar makes a good receptacle as it can withstand the high heat of the boiled sugar solution. A tall, skinny olive jar also makes a good container as it will use a less liquid than a standard canning jar. Tie one end of the cotton string to a pencil and the other end to a paper clip or galvanized washer to provide weight to the string. Wet the string and roll it in granulated sugar.

Stretch out the string, place it on a paper towel and allow it to completely dry. The granulated sugar on the string will attract the sugar crystals and give them something to attach themselves to as they grow. Put the string into the glass jar, paperclip ends hanging straight down and lay the pencil across the top of the jar to hold the string in place. Make sure the string does not touch the sides or the bottom of your container.

Bring 1 cup of water to a rolling boil. Slowly add the granulated sugar, stirring constantly with the wooden spoon to allow the sugar to completely dissolve. Continue adding the sugar a spoonful at a time until the water reaches total saturation and will not dissolve any more sugar. Cook the sugar water solution to a temperature of 240 degrees Fahrenheit. Let the sugar solution cool slightly and then re-heat and dissolve as much sugar as the re-heated solution will hold. The additional sugar will help increase the size of the rock candy crystals. Remove the pan from the heat and then add a few drops of flavoring agent of choice and a few drops of food coloring (optional).

Carefully pour the hot sugar solution into the jar, being extremely careful as this hot sugar solution can cause painful burns.

As the water evaporates, crystals will begin to form along the string within a few hours. Let the sugar crystals grow for approximately a week being careful not to bump or move the container. You might even cover the top of the container with a small towel to keep it dust-free.

The crystals should take a minimum of three days and a maximum of about seven days to completely form. When the sugar has stopped growing, or the crystals have grown to the desired size, the candy is ready to eat. Store any left-over candy in an airtight container.

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