Supersaturation. Sucrose crystal growth has been studied extensively,
as summarized by Hartel and Shastry (1991). For the most
part, sucrose crystal growth rate increases linearly with increasing
supersaturation at concentrations below the point where molecular
mobility becomes a limiting factor.
As with nucleation, crystal growth rate increases as supersaturation
increases, up to the point where decreased molecular mobility
limits diffusion and growth rate decreases. For example, at room
temperature, an increase in sweetener concentration above the saturation
concentration initially results in increased growth rate as
supersaturation increases. At some point, however, the increased
concentration leads to a decrease in the ability of molecules to
diffuse and growth rate begins to decrease. When the sweetener
concentration is high enough (water content low enough) so that
the glass transition temperature of the mixture reaches room temperature,
mobility is sufficiently decreased and growth of sugar
crystals is shut down completely.