Abstract: Various implementations of a freeze-drying method are described where the material is cooled by reducing the pressure in a chamber to evaporate and/or sublimate water in the material. In one implementation, the material is dried in the chamber by sublimating ice in the material to water vapor. In another implementation, the freeze-drying method includes actively cooling the chamber. In another implementation, at least a portion of the water vapor is deposited on an actively cooled interior surface of the chamber. In another implementation, the freeze-drying method includes cooling the material to ?25° F. or below. In another implementation, the material is cooled at approximately ambient pressure to 30° F. or below and then cooled by reducing the pressure in the chamber.

Abstract: A freeze drying method includes decreasing pressure to a first vacuum pressure and, as a result of reaching the first pressure, a control system automatically activating a heater. The method includes sublimating solid water, increasing pressure to a second vacuum pressure greater than the first pressure, and, as a result of reaching the second pressure, the control system automatically deactivating the heater. As a result, a decrease in pressure, pressure-activated heater activation, material heating, water sublimation, and increase in pressure occur, accomplishing pressure-activated heater cycling. Another freeze drying method includes decreasing a temperature in a chamber to ?50° F. or less using a refrigeration system with single-stage compression and sublimating solid water at a vacuum pressure. A freeze drying apparatus includes a chamber, a vacuum pump, a heater, and a control system programmed with instructions operable to accomplish pressure-activated heater cycling.