Particles, Temperature, and Stirring Influence Crystallization

The crystal “seed” is an initial surface to which sugar molecules can attach themselves and accumulate in a solid mass. The seed can be a few sugar molecules that happen to come together during random movements in the syrup. Stirring and agitation have the effect of bumping solution molecules together more often than they otherwise would, and thereby encourage the formation of crystal seeds. Other things can also serve as seeds in a cooling syrup and initiate crystallization. Among the more common are the tiny crystals that form when the syrup spatters on the side of the pan or dries off on a spoon, and that then are stirred back into the syrup. Dust particles and even tiny air bubbles can also act as crystal seeds. A metal spoon can induce crystallization by conducting heat away from local areas of the syrup, cooling them and so leaving them super-supersaturated. Experienced candy makers therefore prevent premature crystallization by using wooden spoons, avoiding agitation of the syrup once it’s cooked and begins to cool, and carefully removing dried syrup spatter from the pan walls with a moist brush.