What I've Learned

My older daughter made hard candy this Christmas. What fun to have science take place so deliciously in our own kitchen. I say science, because in making hard candy, she turned a crystallized substance into a non-crystalline solid, which is to say, she turned sugar into glass.

Common glass that we use for windows, bottles, jars, and so on, is made from sand. Silica (sand) is an excellent material for this because it readily forms a non-crystalline solid when melted and cooled. Silica is but one of a number of materials that will do this. Certain metals and polymers will do it, as will some types of ceramics. And, of course, sugar.

In movies, when someone is thrown through a plate glass window or is smashed on the head with a bottle, the glass is made from sugar. Or at least, it used to be. These days, it is made from hydrocarbon and ethylene vinyl acetate resins so it is easier to handle, looks more like common glass when it breaks, but is still safe for the actors.

Movie glass, whether made from sugar or modern resins, is, scientifically, real glass. The fact that it breaks easily and safely doesn't change what it is.

At home, turning sugar into glass is not difficult. Simply mix sugar with water and boil the water away at a high temperature. A candy thermometer is needed to make sure you get it right.

Detailed instructions for making sugar glass – that is to say, hard candy – can be found in cookbooks and online, but here is the general idea. (Be careful. Hot melted sugar splashed on your skin can disfigure you for life.)

Because the goal is to end up with a non-crystalline solid, we must first dissolve all the sugar in water to make sure there are no sugar crystals.

Next, we boil it to what is called the hard crack stage. The sugar water will pass through two other stages along the way.

When it reaches 230° to 250° degrees Fahrenheit, it arrives at the thread stage. If some of the mixture is dropped into cold water, it forms threads that will soon dissolve.

At 240° to 250°, the mixture is at the firm ball stage. If some of it is dropped into cold water, it forms a mass that you can take out and roll into a ball. The ball will not get hard, though. It will stay malleable.

The target temperature for hard candy is 300° to 310°, at which point it is but 2-percent to 3-percent water. If poured onto a cold surface, the mixture will begin to cool and will be, for a time, malleable enough to roll out and cut into pieces. At this stage, colorings and flavors can be added and worked in, though in many recipes, these are added at the beginning.

If you don't cut it before it completely cools, it will have to be broken to get smaller pieces. Hard candy, unlike sugar glass in movies, can have sharp edges when broken, so some candy makers put the hardened pieces in a special tumbler that smooths the edges the way the ocean smooths sea glass.

My daughter's candy – pale pink and green and purple – is a delight. And we've discovered that any occasional sharp pieces can be carefully sucked to smoothness in the tumbler nature gave us.