Candy and Crystal Chemistry

Enlarge Image Image Gallery If you can resist scraping that bowl until the appropriate time, you could end up with fudge that looks like this. Lori Dunn

You’re determined. You can do it. You can make perfect fudge. Not the grainy, sugary kind you made last year, but the smooth, melt-in-your-mouth sweetness that your grandmother used to make. You’ve researched; you now know a firm ball from a hard ball from hard crack, and you’re armed with a candy thermometer, just in case. You’ve read up on the proper procedure and have your pastry brush ready to catch any errant sugar crystals that might threaten the creamy smoothness. (Read more about controlling crystallization in Comfort Foods, Page xx.) But, this seems like a lot of extra work. What’s the point of all of this? Must I waste all that yummy fudge by not scraping the pan? Why does all this happen? To understand fudge, you need to understand a couple of things – crystals and supersaturated solutions.

First, crystals. Sugar is a crystal. If you look at table sugar, this seems obvious – tiny, hard grains of sweetness. It’s made up of many identical molecules (sucrose) that find it easy to stack together tightly and become crystals. This is sugar’s tendency that we must fight to keep our fudge creamy instead of gritty.

Honey and maple syrup are solutions of various types of sugar molecules (such as glucose and fructose) and other ingredients dissolved in water. Their natural state is liquid (unless the honey or syrup sit around long enough that the sugar concentration becomes high enough to crystallize).

On the way to a supersaturated solution, let’s talk about saturation. Saturation is what happens when you’ve dissolved all of something that you can in a fluid. If you sneak two extra packets of sugar into your already super-sweet iced tea, and no amount of stirring gets rid of the crystals that fall to the bottom, it’s because your tea has reached saturation. One way that you can increase the saturation amount is to heat your tea. Heat energizes the molecules in the liquid and makes room for more sugar to dissolve. (Maybe you notice less sugar in the bottom of your glass as your tea warms up?) So, as you heat water and sugar, more of the sugar will be dissolved in the water.