The eutectic temperature (triple point) is the temperature at which your sample only exists in the solid phase. If your frozen sample goes to a temperature higher than the eutectic temperature, it will begin to melt.

What is annealing in lyophilization?

Annealing is a processing step in lyophilization in which samples are kept at a determined subfreezing temperature above the Tg', during a period of time (Searles et al., 2001a). This process influences the size distribution of ice crystals, leading to their growth.

What is melt back in lyophilization?

Meltback is a form of cake collapse and is caused by the change from the solid to liquid state. That is, there is incomplete sublimation (change from the solid to vapor state) in the vial. Associated with this problem is a change in the physical form of the drug substance and/or a pocket of moisture.