Crack, speed ball…oh no wait, that’s what Lindsey Lohan had for breakfast this morning. What I meant to say was thread, soft ball, firm ball, hard ball, soft crack, hard crack. These are the terms for the sugar syrups used in the confectionery arts. What’s the difference between them? Simply, the degree to which they’ve been “cooked.”
I use the scare quotes because “cooking” is something of a misnomer when it’s applied to sugar. Why? Because up to about 320 degrees Fahrenheit (the point at which sucrose molecules begin to break into pieces and turn to caramel), sugar is mostly impervious to temperature. It has no proteins to coagulate or starches to gelatinize like most of the other foods we expose to heat. Molecularly speaking, sucrose stays just as it is through all the various candy-making phases, though admittedly it does start to yellow a little the higher you go.
So what’s the difference then between thread-stage syrup and hard crack syrup? By now I’m sure you know the answer: moisture content. Softer syrups simply have more water in them than harder ones. By cooking them all we’re doing is boiling water out to whatever degree we need. The temperature of a syrup, therefore, is as much a measure how much water the syrup contains as it is the heat energy it contains.
This explains why candy making can take so darn much time. Anyone who’s ever attempted to make candy can relate to the experience of standing over a pan of simmering syrup, watching the thermometer slowly tick upward. The higher the temperature goes, the longer the heating process takes. Why?
The answer is because in the early stages of boiling the syrup, most of the heat energy that’s going into the pan is being used to launch water molecules into the air (i.e. create steam). So even though there’s plenty of heat energy entering from the burner below, not much of that energy is being put toward raising the syrup’s temperature. That’s only true up until a point, however. Once the syrup reaches a certain concentration (about 80% sugar), there’s very little evaporation going on. At that point (320 degrees Fahrenheit or so) the temperature of the syrup starts accelerating rapidly. This is why it’s so easy to burn a pan of caramel.
But where was I? Oh yes. It’s interesting to consider that the temperature of the syrup can only go up as water leaves the pan. It’s an interesting experiment to add a teaspoon or so of water back to the pan (carefully of course…that stuff is VERY hot). No matter how hot the water is, the temperature of the syrup goes down, not because it’s spreading coolness around or anything like that, but because the water is changing the syrup’s boiling point. That’s good geek fun.