Xylitol is an organic, non-toxic, biosourced phase change material with high potential for seasonal thermal energy storage material. It has a high energy density, a high and stable undercooling allowing storing solar energy at ambient temperature thus, reducing thermal losses and the risk of spontaneous nucleation (i.e., the risk of losing the stored energy). When the energy is needed, the discharge triggering of the storage system (i.e., Nucleation triggering of highly viscous undercooled Xylitol) is very difficult as well as reaching a sufficient power delivery (i.e., the control of the subsequent crystal growth rates). Both are the mains locks for the use of Xylitol in seasonal energy storage. Different techniques to crystallize highly undercooled Xylitol have hence been considered. It has been proven that nucleation triggering of highly undercooled Xylitol using an air lift reactor would allow reaching performances matching with building applications (i.e., at medium temperatures, below 100 °C). The advantages of this technique compared to other existing techniques to activate the crystallization are discussed. The mechanisms triggering the nucleation are investigated. The air bubble generation, transportation of nucleation sites and subsequent crystallization are discussed to improve the air injection operating conditions.