The Rock Candy Recipe

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My father-in-law is a chemical engineer working at a large pharmaceutical company. Last month, I wandered around the facilities as part of Family Day. Because cameras were prohibited, my only keepsake is the recipe for rock candy, which we were given in a lab devoted to growing crystals. I will now pass along that recipe to you.

You will need:

1) 21 ounces of sucrose (table sugar)
2) 8 ounces of tap water
3) a pot, beaker or saucepan
4) a candy thermometer
5) a spoon
6) a stove
7) glass jar or drinking glass
8) an adult to help*

Recipe:

Add the sugar and water to the pot and stir with a spoon until wet but not dissolved. Heat the solution and stir constantly until the solution measures 170 degrees Fahrenheit with the candy thermometer. Do not stir with the thermometer -- it is fragile. Remove the solution from the heat and continue to stir until the temperature reaches 125 degrees. Pour the hot (!) solution into the glass jar or drinking glass and cool to room temperature. If you want to, add a few drops of your favorite color of food coloring to the solution. Seal or close the container.

You should see some crystals after 2-3 days and if you wait one week, you should see really big crystals! You can grow more and even larger crystals if you punch holes in the top of the container and let the water slowly evaporate -- this can take several weeks.

If you want to grow crystals on a wooden stick or piece of string, soak the string or stick (a toothpick works well) in water and roll in sugar. Allow to dry. Follow the instructions above to the point where the solution is at room temperature. Now place the stick or string into the solution. Once the crystals have grown, remove the stick and allow to dry. This is called a seeding experiment, and this is how rock candy on a stick is made.

Another option:

If you don't have a candy thermometer or faith in your ability to not burn yourself, buy rock candy here, in bulk.

* There is no shame in making this yourself if you are an adult. It's tasty and rewarding.

May 4, 2007 - 5:27am
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