Intensification of freeze-drying rate of coffee extract by vacuum freezing

The objective of this work was to evaluate the use of vacuum freezing (VF) as a new method for the freezing stage in the freeze-drying cycle of coffee extract. In this context, the freeze-drying process was evaluated using either vacuum freezing (VF-FD) or contact freezing (CF-FD) as initial stage. The incorporation of VF in the freeze-drying cycle allowed to reduce up to 1/4 of the initial moisture in the freezing stage, reducing the amount of water that needs to be removed in the subsequent stages (sublimation and desorption). The extremely porous structure formed during VF leads to sublimation rates three times higher in comparison to CF. Moreover, the VF-FD instant coffee showed a higher retention of volatile compounds. Thus, the results presented in this work indicate that vacuum freezing is an efficient approach to improve the freeze-drying rate of aqueous solutions in which the aromatic profile is relevant.