Crack, speed ball…oh no wait, that’s what Amy Winehouse 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 phases that a sugar syrup passes through as it “cooks”. The names are inspired by the form a drop of the syrup takes when it’s immersed in a glass of cold water (a method for assessing the hardness of candy that goes back some 400 years).
But really, what does it mean to “cook” sugar? For up to about 320 degrees Fahrenheit (the point at which sucrose molecules begin to break into pieces and the syrup begins to turn to caramel), sugar is for all intents and purposes impervious to temperature. It has no proteins to coagulate or starches to gelatinize like most other foods exposed to heat. Molecularly speaking, sucrose stays just as it is through all the various candy-making phases.
So what’s the difference then between “thread”-stage syrup and and hard crack syrup? 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 more a measure of the proportion of water the syrup contains than its relative “heat”, which as I mentioned is meaningless for sugar until it gets up over 320 or so.
To make poured fondant we heat sugar syrup to 238 degrees, which is quite soft indeed, merely “soft ball” stage. Yet as anyone who’s tried cooking sugar like this can attest, it still takes quite a while. Standing over a boiling pan of syrup watching the thermometer painstakingly tick upward, well…it can feel like an eternity. The reason for this is that in the early stages of candy making, most of the heat energy that’s going into the pan is being used to launch water molecules into the air. Only once that water is gone can the temperature of the syrup go up. It’s actually a very interesting experiment to add a little water back to the pan (carefully of course…that sticky stuff is VERY hot). No matter how hot the water is, the temperature of the syrup goes down, not because it’s being “cooled” by the water exactly, but because the moisture is changing the syrup’s boiling point. Call it geek fun.
But of course the longer you “cook” your sugar syrup the faster it heats, simply because there’s less water to evaporate. This is why it’s so easy to overshoot the mark with hard sugars and especially caramel, which will burn in the blink of an eye if you aren’t careful.