The size of the resulting crystals depends on the number of nuclei, rate and temperature of crystallization, agitation and impurities in the solution. Crystallization is a complex process with many interrelated factors. The nature of the crystallizing substance is important for crystallization, although not as obvious in candy making as sucrose is almost always the substance under discussion. The rate of crystallization is the speed at which nuclei grow into crystals. At a higher temperature the rate of crystallization is slow and becomes more rapid at a lower temperature.
Agitation distributes the crystal forming nuclei and hastens crystallization.
Impurities in the solution usually delay crystallization and in some cases such as caramels may prevent crystal formation. Fat and protein decrease the number and size of crystals through the interference of their masses with the orientation of the sucrose molecules. Cream of tartar as an added ingredient in a candy formula serves indirectly to decrease the rate of crystallization as well as crystal size. It does this through its ability to hydrolyze sucrose into its invert sugar. This not only forms two sugars of greater solubility than sucrose, but it gives agents which enhance the solubility of sucrose.