By Harold McGee
Crystal size and texture are also influenced by stirring. We’ve seen that agitation favors the formation of crystal seeds by pushing sugar molecules into each other. A syrup that is stirred infrequently will develop only a few crystals, while one that is kept in motion continuously will produce great numbers. And the more crystals there are in a syrup, all competing for the remaining free molecules, the fewer free molecules there are to go around, and so the smaller the average size of each crystal. The more a syrup is stirred, then, the finer the consistency of the final candy. This is the justification for wearing your arm out when making fudge: the moment you let up, the formation of seeds slows down, the crystals you’ve made up to that point begin to grow in size, and the candy gets coarse and grainy.