A batch of all beef tallow (BT)-based model shortening (divided into six rectangular block samples) was stored under temperature fluctuation cycles of 5-20 °C until granular crystals were observed. The lipid composition, thermal properties, and polymorphism of the granular crystals and their surrounding materials were evaluated. Furthermore, the isothermal crystallization behavior of two parts noted above was also examined by pulsed nuclear magnetic resonance (pNMR), rheology, and polarized light microscopy (PLM). The changes of nanostructure including the aggregation of high-melting triacylglycerols (TAGs) and transformation into the most stable β polymorph occurred in granular crystals compared with surrounding materials. Concomitantly, a slower crystallization rate with a simultaneous increase in crystal growth led to the formation of large crystals and further aggregated to larger granular crystals when the size ultimately exceeded the sensory threshold.