To overcome disadvantages of freeze-drying that is usually lengthy and expensive

a novel idea

freeze-drying of initially unsaturated porous frozen material

was proposed.An experimental investigation was performed to verify the effect of unsaturated frozen materials with a certain initial porosity on freeze-drying of liquid materials.A multifunctional freeze-drying apparatus on the lab scale was designed

made and assembled.Mannitol was selected as the primary solute in the solution.Liquid nitrogen ice-cream making method was used to prepare frozen materials with different initial saturations.Results show that the unsaturated frozen material can enhance the freeze-drying process significantly and the drying time is reduced substantially compared to conventional freeze-drying for the same material quantity and initial moisture content under the same operating conditions.The drying time with the unsaturated material (initial saturation=0.28) was 36.4% shorter than that with the conventional one(initial saturation=1.00).The smaller the initial saturation is

the shorter the drying time is and the lower the moisture content of dried products is.