Grow Your Own Rock Candy

Step 4: The Science

Now for the learning part of this delicious treat.  I'm not a professional in the area, nor do I use the most politically correct vocabulary for the subject.  I do however, know enough to explain the basic principles.

Sugar naturally has a crystalline structure, which would be noticed under a microscope with the individual grains.  

A solvent (in this case, water) can only dissolve a certain amount of a solute (in this case, sugar) before it becomes fully saturate.  

By heating the water, it is able to dissolve more and more sugar.  This becomes known as a supersaturated solution.  

We allow the water to absorb the most sugar it can by heating it to it's boiling point of 212°F (100°C), but try to avoid caramelizing and burning the sugar.

As the water cools, it can no longer hold the same amount of sugar we added.  This sugar is "seeded" on the skewer or string, but will not grow on the clean glass surface or perhaps a nylon string or fishing line.  The sugar "regrows" into a crystalline structure.

Comments

[Saturn V]

Mine isn't growing on the skewer, it's recrystallizing on the top. Why is this? The skewer was straight down the middle, 1 inch from the bottom.

[JBarker09]

I've noticed with mine if they start growing on top, it won't grow on the stick. If i take a fork or something and poke the surface so the liquid is exposed again it started growing. I have no explanation for this, but I hope to find out the answer in my fluid mechanics class this semester at Arizona State.

[yanksguy]

Pull out the stick and reheat the solution. The crystals on top will go back into the solution and then you can put the stick back in and continue. Once crystals form new crystals will want to connect with them. If you only allow crystals on the stick, that's the only place they will grow.

[Saturn V]

Ah. Now some is finally growing on the stick, but it's just a very tiny bit. Some of it's even growing on the glass. Darn variables!

[beehard44]

decant it into a new glass when it grows in the side
you can break it up and eat the crystals

[JohnDeere312]

Love how you put some science into this! Very interesting!