All sugar candies, whether brittle or creamy or chewy, are essentially mixtures of two ingredients: sugar and water. Cooks manage to create very different textures from the same materials by varying the relative proportions of sugar and water, and the physical arrangement of the sugar molecules. They control the proportions as they cook the sugar syrup, and they control the physical arrangement as they cool it. Depending on how hot the syrup gets, how quickly it cools, and how much it’s stirred, it can solidify into coarse sugar crystals, fine sugar crystals, or a monolithic crystal-free mass. To a large extent, the art of the confectioner depends on the science of crystallization.